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

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Abstract
When New York lettuce seeds were imbibed below 20°C in the dark, full germination was observed, whereas none occurred above 35°C even under red-light irradiation. Partial treatment with high temperature during imbibition revealed the involvement of a thermo-labile process in the germination. This process was completely inhibited above 30°C in the dark, but re-activated by the following incubation below 20°C. The longer the seeds were preincubated above 30°C, the longer the period below 20°C required for re-activation. The results suggest that the thermo-labile process is controlled by a thermo-labile factor. The factor was inactivated slowly at 25°C and rapidly above 30°C to a form which could be re-activated below 20°C but was irreversibly inactivated when the seeds were imbibed at temperatures above 45°C for more than 40 hr. The escape reaction of the phytochrome system proceeded even at 35°C whereas no germination was observed at that temperature. Thus, die germination of lettuce seeds is regulated not only by the phytochrome system but also by the thermolabile factor.

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