Mediation of Phytochrome in the Inductive Action of Low Temperature on Dark Germination of Lettuce Seed at Supra-Optimal Temperature

Abstract

The induction of dark-germination in lightrequiting lettuce (Lactuea sativa) seed at supra-optimal temperatures by cold-treatment (in darkness) was partly reversed by a brief far-red irradiation made at time of transfer, and even more so when the irradiation was made at the beginning of the cold-pretreatment. When the inhibitory far-red irradiation was followed by additional cold-treatment, the promotion was greatly restored. The promotive effects of brief irradiationswith red light were further enhanced by a following cold-period, before tranfer to the supra-optimal temperature. These results are interpreted as indicating that the active (far-red absorbing) form of phytochrome is pre-existing in the dry seed, and interacts with a co-factor which is built-up during inhibition. The rate of buildup of this co-factor, as well as the dark-inactivation of active phytochrome increase with temperature. The products of the interaction pass through a photo-labile thermo-stable phase, before becoming photo-stable as well.