LETTUCE SEED GERMINATION - EFFECTS OF HIGH TEMPERATURE AND OF REPEATED FAR-RED TREATMENT IN RELATION TO PHYTOCHROME

Abstract— At 37°C the active form of phytochrome in lettuce seed cannot function to promote subsequent germination. This effect of high temperature is distinct from thermal acceleration of dark reversion from the active form of phytochrome to the inactive form, and may be due to reversible denaturation of phytochrome. Repeated brief irradiations with far‐red light inhibit subsequent germination in the whole seed, whereas a similar irradiation regime results in a strong enhancement of the development of growth potential (ability to expand against an externally‐imposed osmotic restraint) in the excised axial portion of the seed. A possible explanation for these two opposing results, in volving two different pigment systems with effective loci in different parts of the seed, is suggested. Copyright © 1969, Wiley Blackwell. All rights reserved