Sugar levels in the pea epicotyl: Regulation by invertase and sucrose synthetase

Abstract

In meristematic regions of the pea epicotyl (plumule and hook), fructose was the predominant sugar (about 1 per cent fr. wt.), sucrose was also present (0·4 per cent) but glucose was barely detectable. In adjacent regions of internode where cell expansion occurred, glucose became the main sugar (1 per cent) and levels of fructose and sucrose declined. None of these sugars was absorbed or utilized for metabolism preferentially by excised sections of any one region of the epicotyl. The distribution of various glucosidase, exo-glucanase and sugar phosphatase activities bore no clear relationship to actual hexose concentrations. However, the distribution of invertase activity was parallel to that of glucose, and sucrose synthetase was most active in regions where fructose and sucrose were concentrated. It is suggested, therefore, that the principal factors controlling sugar levels in the pea epicotyl are location and relative activities of these two enzymes, both utilizing translocated sucrose as substrate.