Hydra Photoresponses to Different Wavelengths
Hydra is photosensitive, although missing known organized photorece- ptive cellular structures. Its contraction-relaxation activity is periodic. Short or long wavelength visible light has opposite effects (respectively long/short main contraction-relaxation period during steady stimulation, low/ high efficiency in interrupting a contraction in progress, long/short reaction time until the next contraction after a pulse stimulation given just after a contraction, decrease/increase of the above reaction time as long as the time of the pulse application after a contraction increases) and they interact on each other (as tested with two stimuli of different wavelengths in close succession). A photocycle mechanism could be hypothesized.
KeywordsHydra attenuata photoreception photoresponse wavelength effect phase response curve
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