SEASONAL VARIATION IN THE ACTIVITY OF NITROGEN ASSIMILATION ENZYMES FROM STRAWBERRY ROOTS

Abstract

Significant seasonal fluctuations in the soluble and insoluble reduced N pools of strawberry roots and crowns suggest seasonal alterations in the activities of the enzymes responsible for nitrogen assimilation. The activities of glutamine synthetase (GS), NADH- and ferredoxin-glutamate synthase (NADH- and Fd-GOGAT), and glutamate dehydrogenase (GDH) were assayed from extracts of `Allstar' strawberry roots sampled at intervals over 12 months from matted row beds. GS activity was high during late winter and declined 16-fold by the summer and fall. Although Fd-GOGAT activity was not detected, NADH-GOGAT activity exhibited over 5-fold higher levels during bloom and fruiting than at other times of the year. GDH activity fluctuated over 8-fold during the year with the highest levels occurring during the spring growth flush and after bed renovation. The seasonal changes in enzyme activities corresponded to significant events in plant development and indicate involvement of these enzymes in N assimilation and cycling in strawberry.