Very low fluence and low fluence response in the induction and inhibition of seed germination in Celosia argentea

Abstract

AbstractSeeds of Celosia argentea L. displayed an absolute requirement for light for germination. Germination could be induced by far-red light as well as red light, and therefore, the effect of red light was not completely reversible by far-red light. A considerable proportion of the seed population was sensitive to red light within the range 0.01–0.1 μmol m−2, which suggested that phytochrome was operating in the very low fluence response mode. Seeds showed a gradual increase in germination in response to red light with an increasing duration of previous dark imbibition. Interruption of the dark imbibition period with very low fluence (10−4−10–1 μmol m−2) or low fluence (1–103 μmol m−2) red light prevented germination subsequent to a terminal, saturating red light irradiation. Increasing responsiveness to red light with increase in imbibition temperature and inhibition of development of photosensitivity by cycloheximide suggested that phytochrome synthesis occurred during the dark imbibition period. An absolute requirement for light for seed germination, inhibition of seed germination on interrupting the dark imbibition period with very low fluence or low fluence red light, and the recovery from photoinhibition of seeds in darkness are consistent with the hypothesis that PhyA is the principal phytochrome involved in the photoregulation of seed germination in C. argentea.