Nasti
Fotonastisk bevægelse hos Sommerfuglekløver (Oxalis triangularis), udløst af lysforholdene. Ved nedsat lysmængde foldes bladene nedad. Tidsforløbet afspilles ved 750 x reel hastighed og dækker i virkeligheden 1½ time.
Foto: Richard Wheeler
Nasti er en plantebevægelse, hvis retning er bestemt af den anatomi, som den bevægende del har. Det er altså ikke afgørende, hvorfra påvirkningen kommer, og den har kun den funktion at igangsætte den forud fastlagte bevægelse. Nastier kan være forholdsvis hurtige og i visse tilfælde også reversible. Ofte henter bevægelsen sin drivkraft i ændrede turgorforhold.
Overblik over forskellige nastier
- Seismonasti: Reaktion på rystelse eller berøring (f.eks. Mimose)
- Kemonasti: Reaktion på kemiske kemiske ændringer (f.eks. Soldug)
- Termonasti: Reaktion på varme (åbning og lukning af f.eks. Krokusblomster)
- Fotonasti: Reaktion på lysændringer ("sovende" blade hos Kløver ved afstenstid)
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Oxalis Triangularis Photonasty Timelapse.ogv
Forfatter/Opretter: Richard Wheeler, Licens: CC BY-SA 3.0
Oxalis triangularis (Purple Shamrock) is a classic example of a plant which responds with movement to external stimulus. The leaves open and close in response to varying light levels with the result that they are open during during the day and close at night. This is true movement (i.e. not growth) and is non-directional with respect to the stimulus making it an example of nastic movement towards light: photonasty. One image captured every 30 seconds for about 1.5 hours, played back at 25 frames per second; ~750x actual speed. The exposure time was progressively increased through the video so the drop in ambient light levels are not seen.
Forfatter/Opretter: Richard Wheeler, Licens: CC BY-SA 3.0
Oxalis triangularis (Purple Shamrock) is a classic example of a plant which responds with movement to external stimulus. The leaves open and close in response to varying light levels with the result that they are open during during the day and close at night. This is true movement (i.e. not growth) and is non-directional with respect to the stimulus making it an example of nastic movement towards light: photonasty. One image captured every 30 seconds for about 1.5 hours, played back at 25 frames per second; ~750x actual speed. The exposure time was progressively increased through the video so the drop in ambient light levels are not seen.