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Hoekom is Pilobolus fototroop?

Hoekom is Pilobolus fototroop?


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Pilobolus is 'n swamgenus waarvan die vrugliggame bestaan ​​uit 'n stingel wat eindig in 'n spoormassa wat deur turgordruk gelanseer word om die spore te versprei. Die vrugliggame groei na lig, wat uiteindelik die rigting waarin die spore gelanseer word, beïnvloed.

Dit blyk dat swaartekrag-gerigte groei voldoende sal wees om 'n opwaartse trajek te verseker, so ek wonder wat die waarde van fototropisme is. Is dit enigsins bestudeer?


Pilobolus

Die van Pilobolus Kom tot U Sinne is 'n multisensoriese ervaring, met lewendige uitvoerings van Pilobolus-werke, transmedia digitale skeppings, en 'n spesiale kreatiewe samewerking tussen Pilobolus en die gehoor.

In hierdie splinternuwe vertoning nooi ons gehore om terug te kom tot hul sinne. en verken die verband tussen die menslike liggaam en die analoogwêreld rondom ons.

Elke optrede van Kom tot U Sinne kulmineer in die wêreldpremière van 'n nuwe werk wat deur die gehoor en dansers in die teater gechoreografeer is.

Gehooradvies: gedeeltes van hierdie program bevat kort naaktheid.

Oor Pilobolus

Pilobolus het in 1971 by Dartmouth College in New Hampshire begin. Moses Pendleton, 'n hoofvak in Engelse letterkunde en landloopskiër Jonathan Wolken, 'n hoofvak in filosofiewetenskap en skermer en Steve Johnson, 'n pre-med student en paalspringer is ingeskryf vir 'n danskomposisie klas aangebied deur Alison Becker Chase. In daardie klas het hulle hul eerste dans geskep, wat hulle “Pilobolus” genoem het—en ’n nalatenskap van beweging en magie is gebore.

Pilobolus crystallinus is 'n fototropiese (lig liefdevolle) swam. Algemeen bekend as "Hat Thrower", sy spore versnel 0–45 mph in die eerste millimeter van hul vlug en hou vas waar hulle ook al land. Die pa van Jonathan Wolken het pilobolus in sy biologie-laboratorium bestudeer toe die groep die eerste keer gevorm het. Die naam was gepas en het vasgesteek.

Die groep het daarna tientalle danswerke saam met sy stigterslede geskep Robby Barnett, Alison Chase, Martha Clarke, Lee Harris, Moses Pendelton, Michael Tracy en Jonathan Wolken. In die meer as vier dekades sedertdien het Pilobolus op Broadway, by die Oscars en die Olimpiese Spele opgetree, en het op televisie, in flieks, in advertensies en in skole en besighede verskyn en meer as 120 danswerke geskep. Die maatskappy gaan voort om die saad van uitdrukking deur menslike beweging na elke uithoek van die wêreld voort te dryf, groei en verander elke jaar terwyl hulle nuwe gehore bereik en nuwe visuele en musikale vlakke verken.


Die wêreldbekende dansgeselskap Pilobolus keer op 26 Maart terug na die Ohio-teater

Vir 47 jaar het die internasionaal bekende bewegingsmaatskappy Pilobolus die grens van menslike liggaamlikheid getoets en die krag van gekoppelde liggame ondersoek. Sy splinternuwe werk, Shadowland: The New Adventure, gebruik die maatskappy se gemengde media-verkenning om 'n liefdesverhaal te vertel oor twee mense wat op soek is na 'n magiese voël. Deur animasie, video en lewendige skadu-teater te gebruik, dompel hierdie dolle avontuur sy tone in die genres van wetenskapfiksie, film noir en romantiese komedie.

CAPA bied Pilobolus aan by die Ohio-teater (39 E. State St.) op Dinsdag, 26 Maart, om 19:30. Kaartjies is $20-$50 en kan persoonlik gekoop word by die CAPA Ticket Centre (39 E. State St.), aanlyn by www.capa.com, of per telefoon by (614) 469-0939 of (800) 745- 3000. Sluit twee handelinge en 'n pouse in.

Oor Pilobolus
Pilobolus het in 1971 by Dartmouth College in New Hampshire begin. Moses Pendleton, 'n hoofvak in Engelse letterkunde en landloopskiër Jonathan Wolken, 'n hoofvak in filosofiewetenskap en skermer en Steve Johnson, 'n pre-med student en paalspringer is ingeskryf vir 'n danskomposisie klas aangebied deur Alison Becker Chase. In daardie klas het hulle hul eerste dans geskep, wat hulle getitel het &ldquoPilobolus&rdquo en 'n nalatenskap van beweging en magie is gebore.

Pilobolus crystallinus is 'n fototropiese (ligliewende) swam. Algemeen bekend as &ldquoHat Thrower,&rdquo, sy spore versnel 0&ndash45 mph in die eerste millimeter van hul vlug en hou vas waar hulle ook al land. Die pa van Jonathan Wolken het pilobolus in sy biologie-laboratorium bestudeer toe die groep die eerste keer gevorm het. Die naam was gepas en het vasgesteek.

Die groep het daarna tientalle danswerke saam met sy stigterslede Robby Barnett, Alison Chase, Martha Clarke, Lee Harris, Moses Pendelton, Michael Tracy en Jonathan Wolken geskep. In die meer as vier dekades sedertdien het Pilobolus meer as 120 danswerke geskep en op Broadway, by die Oscars en die Olimpiese Spele opgetree, en het op televisie, in flieks, in advertensies en in skole en besighede verskyn. Die maatskappy gaan voort om die saad van uitdrukking deur menslike beweging na elke uithoek van die wêreld voort te dryf, groei en verander elke jaar terwyl hulle nuwe gehore bereik en nuwe visuele en musikale vlakke verken.


Oor die Maatskappy

Pilobolus "Shadowland"

Pilobolus het in 1971 by Dartmouth College in New Hampshire begin. Moses Pendleton, 'n hoofvak in Engelse letterkunde en landloopskiër Jonathan Wolken, 'n hoofvak in filosofiewetenskap en skermer en Steve Johnson, 'n pre-med student en paalspringer is ingeskryf vir 'n danskomposisie klas aangebied deur Alison Becker Chase. In daardie klas het hulle hul eerste dans geskep, wat hulle getitel het &ldquoPilobolus&rdquo &mdash en 'n nalatenskap van beweging en magie is gebore. Pilobolus crystallinus is 'n fototropiese (lig liefdevolle) swam. Algemeen bekend as &ldquoHat Thrower,&rdquo, sy spore versnel 0&ndash45. Lees meer

Pilobolus het in 1971 by Dartmouth College in New Hampshire begin. Moses Pendleton, 'n hoofvak in Engelse letterkunde en landloopskiër Jonathan Wolken, 'n hoofvak in filosofiewetenskap en skermer en Steve Johnson, 'n pre-med student en paalspringer is ingeskryf vir 'n danskomposisie klas aangebied deur Alison Becker Chase. In daardie klas het hulle hul eerste dans geskep, wat hulle getitel het &ldquoPilobolus&rdquo &mdash en 'n nalatenskap van beweging en magie is gebore.

Pilobolus crystallinus is 'n fototropiese (lig liefdevolle) swam. Algemeen bekend as &ldquoHat Thrower,&rdquo, sy spore versnel 0&ndash45 mph in die eerste millimeter van hul vlug en hou vas waar hulle ook al land. Die pa van Jonathan Wolken het pilobolus in sy biologie-laboratorium bestudeer toe die groep die eerste keer gevorm het. Die naam was gepas en het vasgesteek.

Die groep het daarna tientalle danswerke saam met sy stigterslede geskep Robby Barnett, Alison Chase, Martha Clarke, Lee Harris, Moses Pendelton, Michael Tracy en Jonathan Wolken. In die meer as vier dekades sedertdien het Pilobolus op Broadway, by die Oscars en die Olimpiese Spele opgetree, en het op televisie, in flieks, in advertensies en in skole en besighede verskyn en meer as 120 danswerke geskep. Die maatskappy gaan voort om die saad van uitdrukking deur menslike beweging na elke uithoek van die wêreld voort te dryf, groei en verander elke jaar terwyl hulle nuwe gehore bereik en nuwe visuele en musikale vlakke verken.


Pilobolus

Pilobolus het in 1971 by Dartmouth College in New Hampshire begin. Moses Pendleton, 'n hoofvak in Engelse letterkunde en landloopskiër Jonathan Wolken, 'n hoofvak in filosofiewetenskap en skermer en Steve Johnson, 'n pre-med student en paalspringer is ingeskryf vir 'n danskomposisie klas aangebied deur Alison Becker Chase. In daardie klas het hulle hul eerste dans geskep, wat hulle “Pilobolus” genoem het—en ’n nalatenskap van beweging en magie is gebore.

Pilobolus crystallinus is 'n fototropiese (lig liefdevolle) swam. Algemeen bekend as "Hat Thrower", sy spore versnel 0–45 mph in die eerste millimeter van hul vlug en hou vas waar hulle ook al land. Die pa van Jonathan Wolken het pilobolus in sy biologie-laboratorium bestudeer toe die groep die eerste keer gevorm het. Die naam was gepas en het vasgesteek.

Die groep het daarna tientalle danswerke saam met sy stigterslede geskep Robby Barnett, Alison Chase, Martha Clarke, Lee Harris, Moses Pendelton, Michael Tracy en Jonathan Wolken. In die meer as vier dekades sedertdien het Pilobolus op Broadway, by die Oscars en die Olimpiese Spele opgetree, en het op televisie, in flieks, in advertensies en in skole en besighede verskyn en meer as 120 danswerke geskep. Die maatskappy gaan voort om die saad van uitdrukking deur menslike beweging na elke uithoek van die wêreld voort te dryf, groei en verander elke jaar terwyl hulle nuwe gehore bereik en nuwe visuele en musikale vlakke verken.

Erkenning aan Land

Ons gee erkenning aan die Eerste Volke – die Tradisionele Eienaars van die lande waar ons woon en werk, en ons erken hul voortdurende verbintenis met grond, water en gemeenskap. Ons gee respek aan ouderlinge – verlede, hede en opkomende – en erken die belangrike rol wat Aboriginal Peoples en Torres Strait Islanders steeds speel binne die World Science Festival Brisbane en Queensland gemeenskap.


'n Nuwe bloulig-fototropiese reaksie word in die wortels van Arabidopsis thaliana in mikroswaartekrag geopenbaar

Bloulig positiewe fototropisme in wortels word deur swaartekrag gemasker en in toestande van mikroswaartekrag geopenbaar. Daarbenewens is die grootte van rooi-lig positiewe fototropiese kromming gekorreleer met die grootte van swaartekrag. As gevolg van hul sittende aard, gebruik plante omgewingsaanwysings om te groei en op hul omgewing te reageer. Twee van hierdie leidrade, lig en swaartekrag, speel 'n wesenlike rol in plantoriëntasie en gerigte groeibewegings (tropismes). Baie min is egter tans bekend oor die interaksie tussen lig- (fototropiese) en swaartekrag (gravitropiese)-gemedieerde groeiresponse. Deur die Europese Modulêre Kweekstelsel aan boord van die Internasionale Ruimtestasie te gebruik, het ons die interaksie tussen fototropiese en gravitropiese response in drie Arabidopsis thaliana genotipes, Landsberg-wildtipe, asook mutante van fitochroom A en fitochroom B ondersoek. Aan boord sentrifuges is gebruik om 'n fraksionele swaartekraggradiënt wat wissel van verminderde swaartekrag tot 1g. 'n Nuwe positiewe blou-lig fototropiese reaksie van wortels is waargeneem tydens toestande van mikroswaartekrag, en hierdie reaksie is verswak teen 0.1g. Daarbenewens het 'n rooilig-voorbehandeling van plante die grootte van positiewe fototropiese kromming van wortels verhoog in reaksie op blou beligting. Daarbenewens is 'n positiewe fototropiese reaksie van wortels waargeneem wanneer dit aan rooi lig blootgestel is, en 'n afname in reaksie was geleidelik en gekorreleer met die toename in swaartekrag. Die positiewe rooi-lig fototropiese kromming van hipokotiele wanneer dit aan rooi lig blootgestel is, is ook bevestig. Daar is ook getoon dat beide rooilig- en blouligfototropiese response beïnvloed word deur rigtingligintensiteit. Na ons kennis is dit die eerste karakterisering van 'n positiewe bloulig-fototropiese respons in Arabidopsis-wortels, asook die eerste beskrywing van die verwantskap tussen hierdie fototropiese response in fraksionele of verminderde swaartekragte.

Sleutelwoorde: Arabidopsis Fraksionele swaartekrag Mikroswaartekrag Fototropisme Verminderde swaartekrag Ruimtevlug.

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Bestudeer notas oor plantbewegings (met diagramme)

Die onderstaande artikel bied 'n noukeurige blik op die plantbewegings. Nadat u hierdie artikel gelees het, sal u leer oor: 1. Klassifikasie van plantbewegings 2. Geotropisme 3. Fototropisme 4. Verduideliking van fototropisme en geotropisme deur die hormoonkonsep 5. Hidrotropisme 6. Chemotropisme 7. Haptotropisme of thigmotropisme 8. Nastiese beweging en 9. Bewegings van pamflette van Mimosa Pudica.

Beweging word gewoonlik nie met plante geassosieer nie en allermins met bome of struike. As ons dink aan beweging in die eng sin van 'n hele organisme wat trans-lokaliseer, dan vind ons baie min gevalle in die plantwêreld. Miskien is die bekendste gevalle wanneer 'n eensellige alg soos Chlamydomanas na lig beweeg of wanneer spermatozoïede deur middel van flagella na die eiersel beweeg. Baie voortbeweging’s is egter outo­matic en is nie afhanklik van enige eksterne stimulus soos getoon deur plasmodesmata van Myxomycetes of amoeboid bewegings wat werklik kruipende bewegings as gevolg van sommige interne stimulus.

Flagella of silia is lokomotiewe organe, sweepagtig in vorm wat die organisme heen en weer beweeg deur 'n proses van sametrekking en uitsetting wat die spiersametrekking van diere herinner, maar eintlik heeltemal anders is as, die spiersametrekking van diere. Bewegings van hierdie tipe word getoon deur gesilieerde plante, gamete en soöspore terwyl die plasmodia van Myxomycetes kruipende, amoeboïede beweging vertoon.

As ons aan die ander kant beweging dink in die sin van 'n deel van 'n organisme wat beweeg as gevolg van ongelyke groeitempo's van die teenoorgestelde kant, dan is die voorbeelde in die plantwêreld talryk. Dele van die plante, hul wortels, hul blare, hul stingels is almal in staat om te beweeg en beweeg in werklikheid voortdurend.

Plante beskik oor prikkelbaarheid en voer bewegings uit in reaksie op 'n verskeidenheid eksterne stimuli wat op die protoplasma van die sel inwerk. Sulke bewegings kan slegs geïnduseer word omdat die stimuli op 'n prikkelbare protoplasma inwerk. Sommige suiwer meganiese bewegings, wat niks met protoplasma te doen het nie, kom algemeen voor in die planteryk, soos wanneer sporangia of vrugte losbreek in die verspreiding van spore en sade en in die op- of ontwikkeling van elaters soos in Equisetum. Dit is suiwer higroskopiese bewegings, wat grootliks bepaal word deur die aan- of afwesigheid van water.

Dit is dikwels gebruiklik om na outonome bewegings te verwys. Dit is bewegings wat klaarblyklik onafhanklik is van die omgewing van plante, dit wil sê van enige eksterne stimulus. 'n Ruwe analogie in 'n man sou die aanhoudende klop van die hart wees wat redelik onafhanklik van die omgewing is, in teenstelling met die reaksie van die hand wat onttrek wanneer dit geskroei word. In laasgenoemde geval veroorsaak 'n eksterne stimulus die move­ment. Miskien is die bekendste voorbeeld van outonome beweging in plante die move­ment wat beskryf word deur die toppunt van die stam van baie plante.

By plante soos ertjies of boontjies sal daar waargeneem word dat die stam se top gereeld 'n sirkelvormige, spiraalvormige tipe groeibeweging beskryf. Hierdie sirkelbeweging wat redelik onafhanklik is van enige eksterne toestande is altyd in dieselfde rigting vir dieselfde plantspesie. Die vinniger groeitempo beweeg om die punt wat, soos dit opwaarts groei, dus moet roteer.

Die onmiddellike oorsaak is dat die groei aan die verskillende kante van die stam verskil. Eers groei die een kant vinniger, dan die ander kant, en dit gaan voort in 'n voortdurende gereelde afwisseling. Daar word na hierdie tipe beweging verwys as mutasie, verkieslik omloop. Soortgelyke tipe bewegings word getoon deur die ranke van baie plante.

Die tweede tipe beweging wat ons gewoonlik by plante ontmoet, is dié wat plaasvind in reaksie op veranderinge in die omgewingstoestande van die plant. Die buiging van luglote wat naby 'n venster na die lig gegroei het, die afwaartse groei van wortels, ens., al hierdie is 'n voorbeeld van die reaksies op veranderinge in die omgewing.

Hier word na verwys as tropismes omdat daar 'n rigtinggewende verband is tussen die reaksie en die veroorsakende effek daarvan - reaksie is óf na die stimulus wat eensydig van slegs een rigting of weg daarvan of teen 'n bepaalde hoek met die rigting van die stimulus optree.

Daar is 'n ander soort beweging (nastiese beweging) waarin die stimulus diffuus is, dit wil sê, dit beïnvloed nie die orgaan vanuit enige bepaalde rigting nie en die beweging, dus geïnduseer deur die stimulus, word uitsluitlik bepaal deur die eienskappe van die prikkelbare selle. Die reaksie van die orgaan hier is onafhanklik van die rigting van die stimulus. Voorbeelde word verskaf deur baie blomme wat oopgaan wanneer temperatuur styg en toemaak wanneer dit daal. Pulvinêre bewegings soos getoon deur die sensitiewe pamflette van Mimosa pudica is altyd nasties van aard en word bepaal deur die eienskappe van die pulvini.

Die omgewingsfaktore wat vir die groeiverskil verantwoordelik is, is beslis bekend en word as die stimulus genoem. Die tydsduur waaraan die plant of die plantorgaan voortdurend blootgestel moet word aan 'n gegewe intensiteit van stimulus vir 'n sigbare reaksie om te volg, word die aanbiedingstyd genoem. Die tydperk vanaf die aanvang van stimulasie tot die aanvang van die reaksie of reaksie word genoem. reaksietyd en die tyd wat dit neem vir die plant om sy oorspronklike posisie te herstel, nadat die stimulus verwyder is, is die ontspanningstyd. 'n Orgaan kan ook 'n stimulus waarneem, maar kan dalk nie daarop reageer nie.

Bewegings kan op verskeie maniere geklassifiseer word. Die klassifikasie wat die bioloog gebruik, is grootliks 'n kwessie van gerief waardeur sekere groepe plantgedrag met mekaar in verband gebring kan word. Die verskille in terminologie is weereens op gerieflikheid eerder as op beginsel gebaseer.

Klassifikasie van plantbewegings:

A. Suiwer Meganiese bewegings wat nie verband hou met prikkelbaarheid van die protoplasma-beweging wat geassosieer word met die verdwyning van sporangia (bv. varing Fig. 750), met plofbare bars van baie vrugte, verspreiding van spore en sade, bewegings van elaters (bv. Marchantia en Equisetum) ensovoorts.

Tropiese bewegings:

In die geval van tropiese bewegings, soos ons voorheen gesien het, toon die bewegingsrigting 'n definitiewe verband na, weg van of teen 'n bepaalde hoek, met die rigting van die stimulus.

Die kromming wat deur 'n orgaan ontwikkel word, wanneer sy voorkeuroriëntasie ten opsigte van 'n omgewingsfaktor versteur word, kan 'n ‘tropiese reaksie’ genoem word. Die omgewingsfaktore dien slegs as snellers wat die metabolisme-weg op so 'n wyse verander dat die energie-aflewerende sisteem van metabolisme die reaksie in staat stel om plaas te vind.

Die omgewing of die eksterne faktor word 'n stimulus genoem - die stimulasieproses self, dit wil sê die heel vroegste veranderinge binne die organisme wat deur die effek van die eksterne faktor teweeggebring word, word nog min verstaan. Die prosesse kan onderverdeel word in onderafdeling en persepsie (resepsie), d.w.s. suiwer fisiese prosesse en die onmiddellik daaropvolgende fisiologiese prosesse onderskeidelik.

'n Beweging na die stimulus word 'n positiewe beweging genoem, weg van die stimulus, 'n negatiewe beweging. Die terme geotropisme, fototropisme, hidrotropisme, chemotropisme en haptotropisme (of thigmotropisme) beskryf bewegings wat onderskeidelik deur eksterne stimuli soos swaartekrag, lig, water, chemiese stowwe en kontak of aanraking veroorsaak word.

Die terme word hieronder beskryf:

Geotropisme:

Die stimulus van swaartekrag moet eensydig wees aangesien die krag slegs vanuit een rigting uitgeoefen word. Primêre wortels is positief geotropies (dws buig na die middel van die aarde), primêre stamme is negatief geotropies in werklikheid alle vertikaal opwaarts-groeiende organe, hetsy stingels, blare, blomstingels, dele van blomme en selfs wortels, bv. aangesien die respiratoriese pneumatofore van baie halofitiese plante beslis nega­tief geotropies is. Wanneer sulke organe uit hul regop posisie gedwing word, kan hulle dit weer inneem as hulle nog in staat is om te groei.

Sekondêre sywortels en lote toon 'n swakker reaksie of geen reaksie nie en neem 'n posisie in 'n hoek met die gravitasiekrag in. 'n Verspreide en skuimende veselagtige wortelstelsel soos by eensaadlobbige is 'n aanduiding van baie swak geotropiese reaksie. Daar word gesê dat sekondêre sywortels plageotroop is en afwaarts gerig is en laterale van hoër ordes, beide wortels en lote is feitlik ongevoelig vir die stimulus van swaartekrag (apogee-tropies). Risome of lopers onder die grond of op die oppervlak, groei horisontaal wat slegs 'n posisionele res­ponse behels, dit wil sê hulle neem 'n posisie in reghoekige posisie in met die rigting van swaartekrag (diageotropies).

Die toevallige pneumatofore van halofiete is negatief geotropies en negatief hidrotropies maar lyk positief aero-tropies.

Die reaksie van 'n orgaan op die gravitasie-stimulus kan verander met die stadium van ontwikkeling. Die steel van 'n papawerblomknop is afwaarts gerig, d.w.s. posi­tief geotropies, maar dit word geleidelik negatief soos die blom oopgaan.

Die eerste teken van geotropiese reaksie vind plaas op 'n kort afstand van die toppunt af (Fig. 752), behalwe by eensaadlobbige, in welke geval dit by die nodusse voorkom waar die meristeme gevind word.

Die geotropiese reaksies kom universeel voor. Wanneer 'n hele plant horisontaal geplaas word, sal sy stam vinnig opwaarts gaan en sy wortels afwaarts. Daar is op 'n tyd gedink dat die afwaartse kromming van horisontaal geplaasde wortels uitsluitlik die gevolg is van hul eie gewig. Maar dit is nou self vasgestel dat geotropiese krommings slegs deur groei moontlik is. Wortels wanneer hulle positiewe geotropiese bewegings uitvoer, dring kwik binne, (Fig. 753) 'n vloeistof waarin dooie wortels dryf. Dat swaartekrag die werkende sti­mulus in geotropiese kromming is, kan maklik aangetoon word as ons alle kante van die plant gelyk aan swaartekrag blootstel.

Dit word gedoen deur 'n plant horisontaal op 'n wiel te plaas wat stadig in die vertikale vlak om 'n horisontale as draai in 'n apparaat bekend as klinostaat (1-4 rotasies per uur). Sodoende word die plant stadig gedraai sodat elke kant op sy beurt in dieselfde mate aan swaartekrag blootgestel word (Fig. 754). Wanneer dit gedoen word, toon die plant of sy dele geen opwaartse of afwaartse kromming meer nie. Dit groei net soos dit geplaas word— reguit langs (Fig. 755).

As ontkiemende saailinge egter in alle moontlike posisies aan die omtrek van 'n wiel vasgemaak word en die wiel baie vinnig om 'n horisontale as draai, word gevind dat die wortels radikaal weg van en al die lote radikaal na die middel van die wiel groei. . Aangesien effekte as gevolg van swaartekrag dieselfde tyd was dat aansienlike sentrifugale krag geproduseer is), het die sentrifugale krag die kromming van die saailinge geskroom, soos swaartekrag normaalweg doen.

Die geotropiese en fototropiese bewegings is as gevolg van ongelyke groei van die twee kante van die orgaan wat weer veroorsaak word deur 'n ongelyke verspreiding van inheemse ouksien. Die gravitasiestimulus moet van sekere minimum tydsduur en intensiteit wees om die reaksie te veroorsaak. Die presiese aard van persepsie van gravitasiestimulus is egter minder duidelik, maar pogings om die verskynsel in terme van sensoriese selle (statosiste) en statoliete te verklaar het merkwaardige resultate gedurende die laaste paar jaar behaal.

Baie plante bevat in sekere selle van wortelpunte groot styselkorrels (amiloplaste) wat onder die effek van swaartekrag binne hierdie sensoriese selle beweeg—statosiste. Hierdie beweegbare styselkorrels was vir 'n lang tyd (sedert 1858) veronderstel om reseptore van gra­vitational stimulus of impuls te wees. Onlangse waarnemings gedurende die afgelope dekade bevestig heeltemal die idee wat inherent is aan die klassieke werke van Haberlandt en andere (1900).

Styselkorrels of amyloplaste vorm normaalweg 'n integrale deel van die gravipersepsiemeganisme in plantorgane en die basiese konsep van statolietteorie word nou algemeen aanvaar. Mitochondria en diktiosome reageer egter ook op gravitasie-stimulus en dieselfde geld ook vir ander sellulêre mikroliggame.

Aangesien diktiosome en vesikels wat daardeur gevorm word op een of ander manier verband hou met metabolisme van selwand, is die samestellings en die vorming van selwand self, en geotropiese kromming behels differensiële ouksien-geïnduseerde groei wat op sy beurt 'n indirekte interaksie van ouksien op selwand impliseer. komponente, kan diktiosome 'n belangrike rol speel in geotropiese kromming.

Fototropisme:

As 'n reël is stingels positief fototroop, terwyl blare plageofototroop of trans&sku fototroop is (Fig. 756). Die voordele wat deur hierdie antwoorde verkry word, is dat assimilerende dele na 'n posisie gebring word waar lig volop her&sku word. Studie van baie blaarmosaïeke toon verbasend min oorvleueling van blare. Die meeste wortels is ongevoelig vir lig.

Slegs by 'n paar spesies, waarvan een wit mosterd (Sinapis alba) is, toon die wortels die reaksie wat 'n mens gewoonlik kan verwag, naamlik negatiewe fototropisme. Die stingels van sommige blomme is posi­tief fototroop nadat bevrugting verby is. Die effek van eensydige ligstimulus kan geneutariseer word deur die plant op 'n vertikale klinostaat te roteer. Geen foto­tropiese kromming vind dan plaas nie.

Die fototropiese verskynsel is 'n baie ingewikkelde en fassinerende meganisme. Die reaksie op lig is beslis kwantitatief. 'n Sekere minimum lig is beslis nodig om 'n reaksie te veroorsaak. Hierdie minimum lig moet vir 'n sekere tydperk gegee word. Daar blyk 'n streng verband te wees tussen die tydperk van verligting en die ligintensiteit.

Beligting wat 'n definitiewe bekende reaksie in plant veroorsaak soos getoon deur die buiging van 'n stam of 'n koleoptiel met 'n meetbare aantal grade, sal in elke geval dieselfde wees as die beligting vir 100 sekondes met 10-voet-kerse of vir 10 sekondes is met 100-voet-kerse soos met 1 000 sekondes met een-voet-kers. Dus produseer 'n gegewe hoeveelheid energie 'n Gegewe hoeveelheid fototropiese kromming en die produk van die ligintensiteit en die tydperk van beligting wat nodig is om 'n gegewe fototropiese reaksie teweeg te bring, is konstant.

Tydperiode kan egter nie onbepaald verminder word nie, daarom is 'n minimum aanbiedingstyd waartydens die lig aan die plant gegee moet word om dit waar te neem. Beide die minimum tyd en die minimum lig wat nodig is om reaksie te veroorsaak is egter baie klein. Die tyd kan so min as 'n breukdeel van 'n sekonde wees en die minimum hoeveelheid lig benodig nie veel meer as die lig van 'n gewone flits (eenvoet-kers) nie.

Hierdie duidelike en eenvoudige ligreaksies hou egter nie stand wanneer hoë ligintensiteite bereik word nie en dan is daar nie meer 'n reguit verhouding tussen reaksie en intensiteit van beligting soos hierbo aangedui nie. Dus as 'n koleoptielpunt vir 1 min verlig word. met 1 000 voet kerse kry ons beslis nie 10 keer die reaksie wat 100 voet kerse vir 1 min gegee het nie. laasgenoemde gee ook nie weer 10 keer soveel as 10-voet-kerse vir 1 min.

Trouens, die reaksie in die vorm van die mate van kromming word progressief kleiner soos die ligintensiteit styg totdat versadigingspunt bereik word. Daar is dan geen verdere toename in die respons deur die intensiteit van ligstimulus te verhoog nie. Inderdaad, as die ligintensiteit baie hoog is, sal die plant of die koleoptielpunt tot van die lig wegbeweeg en nie daarheen nie.

Soos in die geval van geotropisme, word dit maklik aangetoon dat die gebied van persepsie en die gebied van reaksie op die ligstimulus nie dieselfde is nie. Die sensitiewe sone is die eerste 1-1,5 mm vanaf die punt.

In die fototropiese reaksie van tweesaadlobbige blare is die vraag na persepsie van stimulus interessant. In die peltvormige blaar van Nasturtium produseer laterale beligting van die hele blaar 'n sterk positiewe kromming van die blaarsteel. Die verwydering van die lamina verminder die omvang van die reaksie drasties.

Aan die ander kant benadeel die sifting van die lamina met swart papier beswaarlik die positiewe kromming van die blaarsteel, terwyl die laterale verligting van die lamina met slegs die blaarsteel geskakeer geen kromming veroorsaak nie. Dit is dus duidelik dat die ligstimulus slegs deur die blaarsteel waargeneem word. Die blaarlem blyk te dien as 'n natuurlike bron van ouksien vir die blaarblare, wat die blaarblaar in staat stel om die groeikromming uit te voer.

Die golflengtes wat fototropiese reaksie teenoor 'n eensydige lig veroorsaak, is beslis nie identies met dié wat by fotoperiodisme of fotosintese betrokke is nie. Die maksimum, soos ons voorheen gesien het, word in die blou gevind, in die omgewing van 450 nm met 'n geringe piek by 480 nm. Fototropiese krommings is egter waargeneem in reaksie op baie korter golflengtes, tot ver in violet. Die fotoreseptiewe pigment is waarskynlik 'n flavonafgeleide, bv. riboflavien (vitamien B)2) of dit kan moontlik β-karoteen of 'n ander karotenoïed wees.

Verduideliking van fototropisme en geotropisme deur die hormoonkonsep:

As 'n koleoptielpunt aan eensydige lig blootgestel word, lei dit tot 'n ongelyke verspreiding van hormone aan die twee kante van die punt en dit kan maklik aangetoon word, deur die hormoon wat uitdiffundeer in agarblokke van die twee kante af te versamel, dat die donker kant het altyd meer hormoon as die kant wat verlig is.

Dit was redelik voor die hand liggend dat lig die vernietiging van hormoon aan die verligte kant van die plant veroorsaak. As dit so is, dan verskyn in die punt van die hawerkoleoptiel of vir die saak in enige sensitiewe streek verligte hormone in verskillende hoeveelhede aan die teenoorgestelde kante van die weefsel. Ander moontlikhede van hierdie ongelyke verspreiding van hormoon in verskillende hoeveelhede aan die twee kante is: (i) dat daar 'n liggeïnduseerde transversale migrasie van hormoon van die ligter kant na die donker kant kan wees of (ii) die sensitiwiteit van die weefsel op die ligter kant van hormoon kan verminder word. In elk geval, in 'n verligte koleoptiel, bevat die donkerder kant beslis meer hormoon as die ligter kant. Die hormoon diffundeer dan afwaarts en bereik die sone van reaksie in ongelyke hoeveelhede, wat verskillende tempo's van selverlenging veroorsaak wat weer kromming veroorsaak.

Vir lig om effektief te wees in enige stelsel soos hierdie, moet dit eers geabsorbeer word om 'n fotochemiese reaksie teweeg te bring, wat lei tot die vernietiging of herverspreiding van ouksien. Aangesien hormone kleurlose verbindings is, is dit duidelik dat hormone nie die absorbeerders van sigbare lig kan wees nie, wat effektief is om fototropiese kromming te produseer. Dit is beslis vasgestel, ons weet, dat nie alle lig ewe effektief is om fototropiese kurwes en shyture te veroorsaak nie.

Blou lig is baie effektief om die beweging te veroorsaak, terwyl rooi lig amper ondoeltreffend en skutend is, die reaksie op ander kleure lig tussen die twee. Van die pigmente wat in die hawerkoleoptiel voorkom, is tot dusver bekend dat slegs twee aktief is in die absorpsie van blou lig.

They are yellow pigments, vitamin B2 (riboflavin) and carotene. The candidatures of both are strong. The action spectrum (the curve relating action, i.e. phototropic curvature to wavelength of light) of phototropism exhibits peaks at about 360 nm and 445 nm with shoulders or minor peaks at 425 and 472 nm. Riboflavin does have an absorp­tion maximum at about 360 nm, but β- carotene has no absorption in this region on the other hand the absorption peaks in the region 400 nm and 500 nm are shown β -carotene whereas riboflavin has only one broad peak at about 460 nm.

The absorption spectrum of none of the pigments thus corresponds reasonably with the action spectrum of phototropism. How­ever, the absorption spectra of isolated pigments may not be identical with the native bound form and thus, either of the pigments or both acting co-operatively may be the photoreceptor pigments.

However, it should be pointed out that a strain of the fungus Pilobolus produces sporangiophores (Fig. 757) which contain no carotene at all but these sporangiophores which are completely carotene-free appear to have retained their full phototropic responsiveness they seem indeed even more sensitive than the normal ones with carotene. Other flavins may also be involved.

It is now generally, believed, and there is good evidence for this, that the photo-tropic curvature is due to lateral transport of auxin from the lighted to the shaded side, and not due to any marked destruction of auxin. In vitro studies however, show that riboflavin may catalyse photolysis of IAA.

Photosensitiser substances are of frequent occurrence in the living cells including plant cells. Riboflavin absorbs blue light and the light energy thus absorbed by the photoreceptor pigment for the phototropic reaction, is thought to be utilised for the photochemical destruction of IAA in the lighter side thereby bringing about the unequal distribution of hormone in the two sides of the coleoptile.

What about the other yellow pigment, carotene, whose absorption spectrum considerably coincides with the action spectrum of phototropism? Can it bring about a similar photolysis of IAA as riboflavin? Available evidence indicates that it is not so. Using aqueous mixtures of IAA and colloidal solutions of carotene or using true alcoholic solutions of both, no photolytic destruction of IAA could be discovered in visible light.

Another possible effect in a different direction which could be produced by the presence of carotene in the system has been examined and the most impressive discovery was that the addition of carotene to the reaction system, IAA+ riboflavin, almost completely inhibits the photo-catalytic action of riboflavin on IAA.

This protective effect seems to be chiefly due to the similarity of the absorption spectra of both the yellow pigments in the critical region where they largely overlap. Carotene may also act as an internal light-filter screening off the most effective wave-length necessary for photo-inactivation of IAA by riboflavin thereby causing a suitable drop in the light intensity across the coleoptile.

It seems certain that there is a strong competition for light between ribo­flavin and carotene and if sufficient light is diverted for absorption by carotene, ribo­flavin can no longer mediate the destruction of hormone. Without carotene, light would reach both sides of the coleoptile in equal amounts as the coleoptile sheath is only about 1.5-2 mm thick. Therefore, the presence of protective carotene filter in the coleoptile could reduce the transverse light gradient, thereby progressively increasing the hor­mone content from the lighted to the dark side.

Many of the observations which have been described for phototropism are also true for geotropism. Thus, the geotropic movement is due to unequal growth which is caused by an unequal distribution of hormones. If an Avena coleoptile tip is placed hori­zontally, the lower part is found to contain as much as 66% of the total hormone content of the tip.

But why should gravity cause such an unequal dis­tribution of auxin? It is worth pointing out here again that reaction of roots to hormones differs from that of stems and the important thing to remember is that while in the stem, the side containing most hormone grows fastest, the opposite is the case in that root.

Thus it must be postulated that the reaction of tissues to particular concentration of hormone is different in the two types of tissues, the shoot and the root. Whereas a parti­cular concentration of hormone induces acceleration of growth in the short end, the same concentration actually produces an inhibitory effect in the growth and enlarge­ment of the root cells. This explains why when a plant is placed horizontally, the stems turn up and the roots down even in absence of light.

The hormone in this case concen­trates on the lower side of the plant (actually growth inhibitors have been identified by chromatographic separation from the upper part of the horizontally placed mesocotyl— the nodal zone between the grain and the coleoptile of maize) resulting in more rapid growth of the cells of the lower side of the stem tissue causing them to bend upwards and faster growth on the upper side of the root tissue, causing roots to bend downwards.

Hence the overall geotropic response is obtained. It has been suggested that the reason for the unequal distribution of auxin in the horizontally placed plant is partly due to the creation of a potential difference across the plant, the lower side becoming positive. This may cause an accumulation of hormone on the lower side of the plant because of the polar flow towards the positive pole, i.e., lower side.

Hydrotropism:

In certain localities, soils do not contain water uniformly some parts may be wetter than others. Primary roots tend to grow towards the wetter regions. The positive hydrotropism of roots may be demonstrated by grow­ing plants in moist sawdust in a shallow sieve, inclined to the vertical (Fig. 758).

Hydrotropism of roots can also be demonstrated as in Fig. 759. The roots grow vertically downwards due to the stimulus of gravity until they penetrate the sieve. They then bend back by growth curvature from the dry air outside towards the moist sawdust. Apparently hydrotropic stimulus is more powerful than gravitational impulse.

Chemotropism:

Chemical substances in the environment have a directive influence on the growth of certain plant structures. The classical example is afforded by the growth of the pollen tube through stigma and style towards the embryosac cell. It is presumed that chemical substances present in the carpels are the directive force for the growth of the pollen tube.

Calcium and boron are the major chemical substances responsible for this movement. When pollen grains germinate in nutrient jelly in which pieces of carpel have been sown, generating pollen tubes grow away from the air and move towards the pieces of carpel the pollen tubes show negative aero-tropism and positive chemotropism.

The first orientation of germinated pollen tubes into the stigma takes place by hydrotropism, followed by a mechanical conduction all along the slimy way. For the final part of the movement of pollen tube through the style, there is no doubt that chemotropic orientation is responsible (Schneider, 1956).

The sucking roots of parasites and hyphae of parasitic fungi penetrate into the tissues of the host plant in response to the stimulus of perhaps other chemical sub­stances contained in them. Movements of individual tentacles of Drosera in response to various chemical substances, both inorganic and organic (in the form of insects), placed in the leaf blade are also examples of chemotropism.

A portion of the chemical substance is absorbed by the leaf, protoplasm is stimulated and a semi-motor impulse goes from the leaf to the bases of surrounding tentacles which bend down on the substance or the insect on the leaf blade. Thus glandular heads of the tentacles are brought in contact with the insect and the organic matter can be digested and assimi­lated by the plant with the help of excreted enzymes.

Haptotropism or Thigmotropism:

The petioles of many species of plants, the leaf tip of Gloriosa, specialised tendrils of garden pea, the stipules of Smilax, the branch of vine, etc., are sensitive to contact with the uneven surface of solid bodies and execute haptotropic curvatures. One of the most remarkable facts is that these structures while sensitive to contact with the surface of a glass rod, is insensitive to that of a glass rod coated with gelatine gel (i.e., a colloidal emulsion). Raindrops, again a liquid, seem to inhibit haptotropic curvature.

It appears that haptotropism results from compression of cells on the stimulated side (i.e., the side in contact with the foreign body) of the sensitive structure while the growth of the opposite side continues. A short curvature is thereby produced and the sensitive structure coils round the support with which it makes contact (Fig. 760).

Though the movement of the individual marginal tentacles of Drosera towards the body of the insects has rightly been described previ­ously as chemotropic movement since the induc­ing stimulus has a directional influence, the first movement of a marginal tentacle towards the small central tentacles, on the other hand, can only be regarded as chemonastic or even haptonastic. This movement is exclusively determined by the properties of the tentacle for the stimulus exerts no directive influence.

Nastic Movement:

When an external stimulus induces a certain process or influences its intensity without attaching any significance to the direction of the stimulus, we have nastic movements. In nastic movements, the direction of curvature is, as we know, morphologically pre-determined. As in the case of tropic movement, nastic movements can be brought about either by unequal growth on the opposite halves of the organ or simply by turgour changes.

Diverse forms of biological advantages may result to the organism from nastic movements. The chemonastic movements shown by insectivorous plants lead to the assimilation of nitrogenous food.

The commonest of nastic movements are nyctinastic movements, the day-and-night movements of leaves and flowers. By nyctinastic growth curvatures, certain flowers can perform opening and closing movements. Perianths and many compound leaves may open during the day and close at night. An interesting nastic movement is observed in some species of cactus the flowers only open in the dark. This is also true for some tobacco flowers.

Some of the nastic movements depend on turgour changes rather than on differential rates in growth: Families, typically showing nyctinastic leaf movements are Leguminoseae, Oxalidaceae, Euphorbiaceae and also pteridophytic species of ferns and Marsilia. The night position of shoot is always characterised by a vertical position of the leaf blade, the petiole curving either upwards or downwards. In the day position the leaf blades stand horizontally or at right angles to the incident light.

Nyctinastic movements may be controlled by temperature and light. These indi­vidual factors acting singly may induce photonastic and thermonastic movements respec­tively. The petals of tulip and crocus open at a constant temperature when illuminated and close when darkened. If on the other hand, the intensity of light is kept constant, they open at high temperature and close at low temperature. They are, therefore, both photonastic and thermonastic. In each case, the opening is the result of growth curva­tures resulting from more rapid growth of the upper surface (epinasty).

When the lower surface grows more rapidly (hyponasty), growth curvature resulting in closure follows. The rolled circinate vernation of young fronds of fern is due to epinastic growth curva­ture its subsequent straightening up is due to hyponasty. Nastic movements are also caused by IAA (auxin epinasty) as well as du6 to the presence of certain substances in minute traces ethylene present in concentration of 1: 500,000 parts of air may cause epinastic movements of tomato leaf petioles.

Nyctinastic movements in some cases appear to have ecological significance in protecting the young leaves or developing flower buds from injury due to light, high temperature and especially by rain. It must be admitted, however, that in most cases, they are in part useless movements.

Movements of Leaflets of Mimosa Pudica:

Perhaps the most striking of all plant movements is that of the semimonastic movements of the sensitive plant, Mimosa pudica. This is also sometimes referred to as haptonastism or thigmonastism. The plant is sensitive to touch, impact, electrical impulses and heat. While the tropic movements are generally, slow taking many minutes, the response of the sensitive plant to any form of shock is almost instantaneous.

Mimosa has com­pound leaves made up of leaflets which in turn are made up of pinnules. When the plant is stimulated by touch, the pinnules begin almost immediately, within seconds, to fold up. If the stimulation is vigorous, this is followed lip by drooping of the whole leaflets at the junction of the petiole.

When a really vigorous stimulation is provided, as for example applying a match to the tip of one of the pinules, the petiole itself droops at its junction with the stem and this is followed by the closing and drooping of all the neighbouring leaves till the leaves of an entire branch have completely folded up.

The whole process is extremely fast and within a minute all the leaves of the branch will have closed. The really important thing is the sequence of closing in the stimulated leaf, first the pinnules, then the leaflets and finally the petiole close up. In the neighbouring leaves, however, the process is completely reversed. Here the petiole drops first followed by the leaflets and only at the last stage do the pinnules fold up in pairs.

The movement of the leaflets of Mimosa is affected by external conditions such as temperature. The leaflets pass into a cold rigour at low temperature and into a heat rigour at about 40°C. The leaflets lose their power of movement in continued scarcity of water and also in continued darkness. The power, of movement is lost also under anaerobic conditions.

The tropic, nastic and various other movements previously described are, as we have seen, caused by differential growth. The movement of Mimosa is, however, very different in mechanism. The pinnules are connected to the leaf-rachis and the rachis is connected to the petiole by swollen leaf bases which are called pulvini (Fig. 752). These pulvini contain cells chiefly situated in the lowest half which normally are com­pletely filled with water, i.e., they are fully turgid.

These turgid cells of the pulvini, however, may readily lose their water to the neighbouring cells and intercellular spaces, as actually happens, due to shock or touch stimulus. When therefore a sudden loss of water occurs from the cells, the lower half of the pulvinus loses its previous rigidity and can no longer support the weight of the leaflet or leaf attached to it which as a result droops downloads.

In view of the extreme rapidity of the response of Mimosa to shock or touch stimulus which almost suggests the nervous response in animals, it seems that a chemical sub­stance is being translocated through the plant very rapidly. There is more than one way of transmitting this shock stimulus. One is very fast and passes in one or two seconds from the pinnule stimulated, to the main petiole pulvinus.

This pathway exists only through living cells (primarily through phloem) of the plant and it has been proved that this stimulus cannot be transmitted through dead tissues. The second, however, is somewhat slower, taking up to a minute or two and it can certainly be transmitted through the dead tissue. The second pathway is apparently the mode of transmission from one compound leaf to the other.

Several workers (1938-1957) have made attempts at the purification and deter­mination of the chemical structure of this stimulating substance in Mimosa, but so for none has succeeded. An amorphous concentrate, extracted from Mimosa, gives the pinna response, at a dilution, 1.5 X10 -8 . This substance behaves as an oxyacid, contain­ing nitrogen (4-5%), with an estimated molecular weight, between 300-450.

Most of the literature concerning the mechanism of rapid movements in plants, particularly Mimosa, concludes that the movements are caused by the diminishing or sudden loss of turgour in the motor cells of the pulvini or decrease in their volume or both. Expulsion of water from the main pulvinus during movement and reabsorption of water during recover have been seen by the use of micropotometer.

Much of the recent evidences do clearly indicate that the motor cells in Mimosa, either in pinna or in pinnules, have contractile vacuoles, whose activity causes liquid— probably cell sap—to be expelled from the motor cells, just like the contractile vacuoles seen in Protozoa this activity might conceivably result in decrease in turgour or the volume of the motor cells. This has nothing to do, however, with the increase in permeability of the plasma membrane.

In 1960, Aimi proved that the sensitive motor cells exist even in the upper-half as well as the lower-half of the main pulvinus. His conclusions were that the magnitude and direction of the petiolar movement in Mimosa is expressed by two forces antagonising each other, each of which consists of bending force, due to the contraction of one-half and tissue tension in the other normally this force, in a downward direction, would be much greater than the upward force. Some differences between the two halves of the pulvinus can actually be observed in the morphology and the activity of the cells—the walls of the cells of the upper-half are actually significantly thicker than that of the lower.

The enzyme ATPase has been identified in the young pulvini but the significance of its presence is still unknown. It may be that the activity of contractile vacuoles or proteins depends on a mechano-chemical reaction caused by an ATP-ATPase system.

How the liquid, which has been expelled into intercellular spaces during response, re-enters the cell interior during recovery is still unknown. An active accumulation of salts or ions, particularly potassium, has been detected in the intercellular spaces of Mimosa petiole and the presumption is that, ATP, working the K-pump takes part in the recovery process of the motor cells, i.e., the re-entrance of the liquid from exterior to the interior of the cells.

It must be admitted that the sensitiveness and the accompanying somewhat com­plicated motor movement of the leaflets of Mimosa do not appear to serve any obvious useful purpose to the plant.


MATERIALE EN METODES

Effect of light availability on axial corallite development

To investigate the relationship of light availability on axial corallite development, the effect of directional light was tested in outdoor aquaria at Heron Island Research Station, Great Barrier Reef, Australia. The aquaria were maintained at ambient temperatures and under natural light conditions, with light in the aquaria measured regularly using a light meter with a manufacturer-calibrated sensor (Li-cor, LI-192S, Lincoln, NE, USA). Same-sized sea water flow-through aquaria that were continuously flushed with water obtained from the reef crest were used for each treatment. The three tested conditions were: side light, top light and open (control). The open aquaria allowed sunlight entry from all sides, but had light shade cloth above the aquaria to reduce the intensity of the midday sun (effectively equalizing the light through out the day). The side-light and top-light aquaria were covered in black plastic, except for a single side or top (respectively) left open. Branches (96 cm×7–8 cm long) were collected from 12 healthy Acropora pulchra colonies on Heron Island reef flat(23°33′S, 151°54′E), Great Barrier Reef, Australia. Axial corallites were removed from the branches by cutting with side cutters approximately 1 cm from the branch tip. Branches were photographed and branch lengths were recorded. In each aquarium, branches (24 per treatment) were suspended, using plastic-coated wire, in the middle of the aquarium. In the side-light aquaria the branches were hung parallel to the water surface and in the top light aquaria the branches were hung vertically. In the control aquaria branches were hung both horizontally and vertically, as controls for both treatments. In all treatments, equal numbers of branches were positioned so that the previous axial corallite end faced towards and away from the light direction, to account for the chance of predetermined growth due to original branch directional growth.

Branches were left to grow in aquaria for 8 weeks. A pilot study demonstrated that this was enough time for A. pulchra branches to develop axial corallites (data not shown). After 8 weeks, branch lengths were measured and branches were re-photographed to record direction of axial corallite development (proximal or distal or both), lateral branch growth and overall branch health. The amount of axial corallite growth at the cut surfaces at both ends of a branch was calculated from the photographs.

Effect of light quantity and quality on axial corallite development

To test the influence of light quantity and quality on axial corallite development, light intensity and quality were manipulated in a field experiment. Branches (288×7 cm to 8 cm) were collected from 16 healthy Acropora pulchra colonies on Heron Island reef flat(23°33′S, 151°54′E), Great Barrier Reef, Australia. The axial corallites were removed from the branches by cutting with side cutters approximately 1 cm from the branch tip. Two branches were placed 1 cm (distal end down) into underwater cement in diagonally opposite cells, of 12 cm×12 cm four-cell seedling trays. A replicate consisted of one seedling tray (two branches Fig. 1). The branches were photographed and initial branch lengths were recorded. The seedling trays were attached to one of four underwater frames(Fig. 1) for exposure to a range of light treatments. Each frame had four replicates of light quantity treatments of 0, 30, 50, 80 and 100% light reduction (using shade cloth or opaque black plastic), and four replicates of light quality treatments of clear (acetate sheet), blue (408–508 nm), red (618–700 nm) and green (482–554 nm) filters (nos 132, 124 and 026, respectively, from LEE Filters, Burbank, CA, USA Fig. 2). Each of the 36 treatments per frame were widely spaced and randomly assigned, to minimize effects of potential differences in flow among positions. The materials used for the various treatments were made into open bottomed boxes approximately 15 cm square with sides of approximately 3 cm. These were fixed to wire mesh (10 cm square) and suspended above the seedling trays to leave approximately 3 cm of the coral branch bases exposed to light and water movement (Fig. 1). This would minimize water flow differences among positions within the frame and allow some light for branches in dark treatments, to avoid branch mortality.

The frames were placed at 4 m depth at Harry's Bommie(23°27.625′S, 151°55.759′E), Heron Island. This nested experimental design resulted in four independent frame replicates for all treatments, and in each frame there were four replicates per treatment.

Coral branches were left to grow for 8 weeks, after which branch lengths were recorded and the amount of vertical axial corallite growth at the cut surfaces was determined by calculating the difference between initial and final branch lengths. Branches were also photographed as a record of the potential lateral encrusting growth at the base, new lateral branch formation and overall branch health (including recovery from handling effects).

Ambient downwelling irradiance (photosynthetically active radiation, PAR)next to the frames was recorded underwater in situ using underwater light loggers (Odyssey, Z412, Christchurch, New Zealand). The logger, a 2πcosine-corrected light sensor was calibrated against a manufacturer-calibrated sensor (Li-cor, LI-192S). In addition, a spectral scan was performed underwater at 4 m at the site of the experiment, on a cloudless day at noon,using a USB2000 spectrometer (Ocean Optics, Dunedin, FL, USA bandwidth of 200–850 nm in a custom-made underwater housing) via an attached optic fibre.

Experimental design of the four frames deployed at Harry's Bommie (4 m) at Heron Island (23°27.625′S, 151°55.759′E), Great Barrier Reef. Arrows point to individual seedling trays (replicates) each containing two Acropora pulchra branches. These were exposed to randomly positioned treatments of 0, 30, 50, 80 or 100% light reduction, or clear,blue, red or green filters.

Experimental design of the four frames deployed at Harry's Bommie (4 m) at Heron Island (23°27.625′S, 151°55.759′E), Great Barrier Reef. Arrows point to individual seedling trays (replicates) each containing two Acropora pulchra branches. These were exposed to randomly positioned treatments of 0, 30, 50, 80 or 100% light reduction, or clear,blue, red or green filters.


Pilobolus

Pilobolus, named after a phototropic fungus, is a modern dance company that was founded by students at Dartmouth College in 1971 and is known for its whimsical and theatrical compositions that rely on collaborative choreography. Since its creation, Pilobolus has performed over one hundred works in more than sixty countries around the world. It has also performed at major events and venues including the 79th Academy Awards, The Olympic games, on Broadway, The Oprah Winfrey Show, Late Night with Conan O’Brien, en The Late Show with Steven Colbert.

Pilobous has received numerous awards including a Primetime Emmy Award for Outstanding Achievement in Cultural Programming, the Samuel H. Scripps American Dance Festival Award for Lifetime Achievement in Choreography, a Brandeis Award, a Berlin Critic’s Award, a Scotsman Award for performances at the Edinburgh Festival, and a Grammy nomination for interactive video in collaboration with OK Go, Google, and Trish Sie.

Pilobolus’ return to Dartmouth was marked by the world premier of B’zyrk, a Dartmouth-commissioned work, the unveiling of the Pilobolus dance archive in the Rauner Special Collections Library, and a lecture given by the artistic directors, a symposium on historicizing modern dance titled, “Leaving Tracks,” an exhibition of Pilobolus dance photographs at Dartmouth’s Hood Museum of Art, and a day of community dance workshops.


Die swam Pilobolus is a common inhabitant of cow and horse manure, or dung. While you and I might consider that a less than ideal place to live, this is high-value real estate for a fungus. The conditions are warm and moist, and there are abundant nutrients. The fungus grows in the dung by forming a network of hyphae, which are threadlike structures composed of cells that are attached end to end. It is the main tissue of the growing fungus. After growing throughout the dung pile for two to three days, the fungus begins a process of forming structures, called fruiting bodies, that are required for asexual reproduction. Fruiting bodies bevat spore. These spores will grow into new fungi under the right growing conditions.

The ideal place for a young spore to start out is on a blade of grass. From there, it can be eaten by a horse or a cow. After passing through the digestive tract unscathed, the spore will, if it is lucky, find itself in a fresh dung pile all its own. But how does the parental fungus solve the problem of getting the spores out of the dung pile and onto the grass? Pilobolus has solved this problem by developing two interesting features: a light-sensitive structure that allows the fruiting body to locate light sources, and a mechanism for firing the sac full of spores toward the light source (a spore sac is also called a sporangium). Why shoot toward the light? Well, imagine a dung pile that is surrounded by trees on three sides. If it shoots the spore sac randomly, three out of four sacs will hit a tree and be lost to the next generation. The side with light is a better bet&mdashit has a good chance of having grass, thus putting the fungal spores in a place where they stand a chance to be eaten by a passing cow or horse.

Pilobolus has evolved mechanisms that allow it to aim and fire in order to place its spores in the best possible spot for survival and reproduction. How does it do it? The stalk below the sporangium becomes swollen with liquid (due to osmotic pressure), with a black mass of spores on the top (see Figure 1, below). Below the swollen tip is a light-sensitive area, which is critical in directing the growth of the Pilobolus so that it faces toward the light. As the fungus matures, pressure builds in the stalk until the tip explodes, launching the spores into the light.

A shiny black spore sac sits on the end of a stalk of Pilobolus. The stalk is filled with a clear liquid and resembles a drop of water turned sideways.


Figuur 1. Dele van die Pilobolus fruiting body. The sporangium contains spores and sits on top of a vesicle containing fluid at high pressure. The sporangium is shot toward a light source, having been aimed in the correct direction by the sporangial stalk. The spore sac reaches accelerations that are among the fastest in nature.



Kommentaar:

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  4. Manawanui

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