Analysis of temperature effect on the germination of New York lettuce seeds

When New York lettuce seeds were imbibed below 20°C in thedark, full germination was observed, whereas none occurred above35°C even under red-light irradiation. Partial treatmentwith high temperature during imbibition revealed the involvementof a thermo-labile process in the germination. This processwas completely inhibited above 30°C in the dark, but re-activatedby the following incubation below 20°C. The longer the seedswere preincubated above 30°C, the longer the period below20°C required for re-activation. The results suggest thatthe thermo-labile process is controlled by a thermo-labile factor.The factor was inactivated slowly at 25°C and rapidly above30°C to a form which could be re-activated below 20°Cbut was irreversibly inactivated when the seeds were imbibedat temperatures above 45°C for more than 40 hr. The escapereaction of the phytochrome system proceeded even at 35°Cwhereas no germination was observed at that temperature. Thus,die germination of lettuce seeds is regulated not only by thephytochrome system but also by the thermolabile factor. (Received August 11, 1975; )