Levels of glucose-6-phosphate and 6-phosphogluconate dehydrogenases in the embryos and endosperms of some dormant and nondormant lines of Avena fatua during germination

Abstract

To investigate the possible role of the pentose phosphate pathway in dormancy and germination of seeds of Avena fatua L., levels of glucose-6-phosphate and 6-phosphogluconate dehydrogenases were analyzed in genetically dormant and nondormant pure lines. Embryos and endosperms of dry mature seeds of each line exhibited high activity for both enzymes. Dehydrogenase levels in the embryos isolated from dormant lines remained constant during the first 48 h of incubation in water, but in nondormant lines there was a sharp increase after 24 h of incubation, well after the onset of germination. Similarly, when seeds of a dormant line were incubated with gibberellin A3 (GA3), there was no increase in dehydrogenase levels in embryos prior to the onset of germination. Thus, in Avena fatua the levels of pentose phosphate pathway dehydrogenases are not involved in the regulation of seed dormancy.In endosperm tissue the pentose phosphate pathway dehydrogenase activity declined rapidly after germination (GA3-induced in the case of the dormant line). The α-amylase activity increased as the dehydrogenase activity declined. Thus, the pentose phosphate pathway appears to be active in endosperm during the early stage of germination, and its dehydrogenases are selectively inhibited, inactivated, or degraded after germination. Unlike α-amylase, the pentose phosphate pathway dehydrogenases were not induced by the exogenous application of GA3 to the endosperm halves.