Transport and Metabolism of Sucrose versus Hexoses in Relation to Growth in Etiolated Pea Stem

Abstract

Sucrose, supplied to detached pea (P. sativum L. cv. Alaska) epicotyls through cut bases, supported better growth of apical tissue than supplied glucose and/or fructose. The hexoses were converted mainly to sucrose in basal regions of the epicotyl, but some moved as such through the epicotyl and accumulated at the apex (plumule) at a rate faster than sucrose. A greater proportion of the C derived from supplied hexoses than from sucrose was used for synthesis of ethanol-insoluble products throughout the epicotyl. By use of asymmetrically labeled sucrose, neither hexose moiety was used preferentially for the synthesis of metabolites. Supplied sucrose moved as such only up to the region of cell elongation where it was hydrolyzed and completely equilibrated before moving into more apical regions. Apparently, better growth with supplied sucrose than hexose could not have resulted from differential effects on cell division, more rapid uptake or transport of sucrose, enhanced wall synthesis or cleavage by sucrose synthase. Evidently, transported sucrose vs. hexoses must undergo or evoke different reactions which affect growth in the region of cell elongation.