ROLE OF PHYTOCHROME-B IN THE INDUCTION OF SEED-GERMINATION BY LIGHT IN ARABIDOPSIS-THALIANA

The role played by phytochrome B in seed germination responses to light pulses was investigated by comparing wild-type (WT) and phyB-1-mutant seeds of Arabidopsis thaliana (L.) Heynh. Similar dark germination rates were observed in WT and phyB-1 seeds stored dry for at least one month. The response of WT seeds to light pulses that established a series of calculated phytochrome photoequilibria was biphasic. In the first phase, i.e. the very-low-fluence response, similar slopes were observed in WT and phyB-1-mutant seeds. In the second phase, i.e. the low-fluence response, the slope of the WT was 30 to 930% higher (depending on the batch, duration of dry storage, and temperature pretratements) than the slope of the phyB-1 mutant. Both hourly pulses of FR and continuous FR promoted germination above dark controls in both genotypes. Phytochrome B is proposed to make a higher contribution to low-fluence than very-low-fluence germination responses of Arabidopsis thaliana seeds.