PHYTOCHROME VARIATION AND REVERSION IN LEMNA MINOR, L. GIBBA G3 AND L. PAUCICOSTATA 6746

— Dual wavelength phot00ometry showed an increase of phytochrome in darkness in partially etiolated plants of three heterotrophically cultured Lemna species. In all three species, Pfr formed by a brief illumination decreased in subsequent darkness with half-lives of 2–6 h. In L. minor and L. gibba, dark reversion was observed during the first 8h of darkness; in L. paucicostata, however, only when the plants were in a slightly anaerobic condition. Under continuous illumination, phytochrome decay was not influenced by light intensity. Actinic doses of far red resulted in non-photoreversible changes of absorbance. In material exposed to red for longer than 12 h, these changes increased after preceding actinic doses of red light. This effect may result in erroneous phytochrome estimations.