Enzymes of sucrose dissimilation as targets for nitrate in early ontogenesis of garden pea

Abstract

We experimentally tested a possibility that nitrate regulates sucrose synthase (SS) in the roots, vacuolar acid invertase (AcI) in the stems, and alkaline invertase (AlI) in the leaves of garden pea (Pisum sativum L.) where they were predominantly located. In the course of early ontogenesis of the seedlings (0–20 days), NO₃^- stimulated solely SS. We detected three peaks of nitrate-dependent enzyme activity: the greatest peak was observed in the very beginning of germination (48 h from seed imbibition), the intermediate peak corresponded to the most intense utilization of cotyledonal reserves (sixth to eighth day of growth), and the lowest peak coincided with development of autotrophy (tenth to 20th day). In the period of their greatest activity (sixth to 14th day), neither invertases noticeably respond to nitrate. At the first peak, NO₃^- affected SS already at a concentration of 1 mM; this influence was maintained at concentrations rising to 10 mM, which points to a signal nature of the effect. We discuss a functional aspect of the effect of nitrate on SS involved in the system of the enzymes of sucrose dissimilation upon the initiation and development of different physiological processes occurring in this period, as well as its possible applied role in agricultural biotechnologies.