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Agardh was investigated under different spectral light conditions in laboratory-grown thalli. <br><br> <table cellspacing="2" cellpadding="2" border="0"> <tr> <td> <!-- <img src="../images/content/" alt=""></img><br> --> </td> </tr> <tr> <td> <!-- <img src="../images/content/" alt=""></img><br> --> </td> </tr> </table> <br> Reference:<br> L&#252;ning, K., "Circadian growth in Porphyra umbilicalis (Rhodophyta): Spectral sensitivity of the circadian system." <u>Journal of Phycology</u> 37(2001): 52-58. <br><br> Abstract:<br> The circadian rhythm in growth of the red macroalga Porphyra umbilicalis(Linnaeus) J. Agardh was investigated under different spectral light conditions in laboratory-grown thalli. A free-running rhythm was observed in constant green or red light at irradiances of 2.5 to 20&#956;mol photons" m<SUP>-2</SUP>" s<SUP>-1</SUP>, whereas arhythmicity occurred in constant blue light at 6 20 &#956;mol photons" m<SUP>-2</SUP>" s<SUP>-1</SUP>. The circadian oscillator controlling growth rhythmicity in Porphyrauses most of the visible sunlight spectrum and possibly multiple photoreceptors with a high sensitivity for blue light and a lower sensitivity for red light. This was inferred from three experimental results: (1) The free-running period,T, of the growth rhythm decreased with increasing irradiance, from approximately 25 h at 2.5 &#956;mol photons" m<SUP>-2</SUP>" s<SUP>-1</SUP> to 22 h at 20 &#956;mol photons" m<SUP>-2</SUP>" s<SUP>-1</SUP> in red or green light, (2) Dark pulses of 3 h duration, interrupting otherwise continuous green or red light, caused advances during the subjective day and delays during the subjective night; the circadian oscillator in Porphyracan discriminate darkness from green or red light, and (3) Low-irradiance blue light pulses (2.5&#956;mol photons" m<SUP>-2</SUP>" s<SUP>-1</SUP>) shifted the growth rhythm in red light of higher irradiance (e.g. 10 &#956;mol photons" m<SUP>-2</SUP>" s<SUP>-1</SUP>), and a strong, high amplitude, type 0 phase response curve was obtained that is usually observed with light pulses shifting a circadian rhythm in otherwise continuous darkness. </td> <!-- Ende des INHALTSTEILS--> </tr> </table> <script type="text/javascript">var gaJsHost = (("https:" == document.location.protocol) ? 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