Changes in protein composition in cellular membranes of various parts of secondary dormant cucumber seeds treated with ethanol

Secondary seed dormancy in cucumber (Cucumis sativus L.) cv. Poinsett 76 co uld be broken with ethanol. Breakage of dormancy was accompanied by signifi cant changes in the composition of membrane proteins in various seed parts. Compared to the intracellular membranes, a change in the protein compositi on of plasma membranes from the embryonic axis and cotyledons was evident e arly in the time-course of ethanol-induced germination of dormant seeds. Wh ile a few alterations in the membrane protein composition in response to et hanol treatment occurred both in dormant and nondormant seeds, a number of changes occurred exclusively in ethanol-treated dormant seeds. Notably, a 1 4 kD protein in the plasma membrane from the embryonic axis and a 35 kD pro tein in the microsomal membranes from the perisperm-endosperm envelope disa ppeared in the ethanol-treated dormant seeds, but not in the ethanol-treate d nondormant seeds. Also a marked decrease in the content of a 23 kD protei n in the plasma membrane from the cotyledons was observed in ethanol-treate d dormant seeds only. It is suggested that the particular changes in cellul ar membrane proteins, which occurred in ethanol-treated dormant seeds much before the first visible indication of germination, might be related to dor mancy breaking rather than to the germination process.