A CONTRIBUTION TO THE STUDY OF DORMANCY IN SEEDS: LACTUCA SATIVA L.

Abstract

The ease with which they may be made dormant by placing them under germinating conditions in blue light suggested that lettuce seed would provide satisfactory material for a study of certain aspects of dormancy in seeds. Studies were made of the behavior of lettuce seeds under varied conditions of moisture, atmosphere, color of light, and integrity of the testa. Measurements of the absolute respiration have provided curves of the drift with time of CO2 output, O2 uptake, and of R. Q. Expts. with substances that might induce dormancy and light-sensitiveness similar to that induced by blue light were made. The bearing of the results obtained upon possible metabolic changes in the seed is discussed. The hypothesis that the observed effects of light on seed germination may be due to changes in the permeability of the seed coat induced by light is considered untenable, but this does not exclude the fact that the seed coat is a restrictive agency to the free passage of O2, CO2, and other substances. Indeed, in any description of the probable metabolic state, this must certainly be considered. While it was not possible to formulate a definite biochemical scheme to account the effects of blue light, the exptl. evidence suggests that "carbon dioxide zymasis" may be promoted by blue light and that CO2 may be one of the inhibiting factors. The blue light dormant condition is characterized by depressed respiration but without more disturbance of the equilibrium of the pre- and postglycolytic phases of respiratory metabolism than is found to be characteristic of uninhibited seeds as reported by other workers. The results of this research suggest that further elucidation of the phenomenon of dormancy should be sought in the direction of more extended studies of the respiration of dormant and non-dormant seeds.