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Control of Senescence in Marchantia by Phytochrome

H. Fredericq^b

^a Department of Biology, Revelle College, University of California, San Diego, La Jolla, California 92037, ^b Laboratory of Plant Physiology, Rijksuniversiteit Gent, Gent, Belgium

Mature green tissue of Marchantia polymorpha L. bleaches markedly when placed in continuous darkness for 4 days but remains green when given daily 1-hour photoperiods of white light. The tissue, however, is induced to bleach when each daily 1-hour photoperiod is terminated with a brief irradiation with far red light. The bleaching does not occur when each irradiation with far red light is followed by a brief irradiation with red light. The bleaching is taken as an index of senescence since the loss of chlorophyll in the bleached tissue is accompanied by a breakdown of cell organelles and cytoplasm. Phytochrome is clearly implicated in the control of senescence by light. It was also found that 5 minutes of red light given once a day was as effective as the 1-hour photoperiods with white light in preventing the bleaching and that bleaching was induced when each daily 5-minute irradiation with red light was followed by a 10-minute irradiation with far red light.