Starch and Sucrose Synthesis in Phaseolus vulgaris as Affected by Light, CO2, and Abscisic Acid

Publisher Website
Google Scholar
Abstract
P. vulgaris L. leaves were subjected to various light, CO2 and O2 levels and abscisic acid, then given a 10 min pulse of 14CO2 followed by a 5 min chase with unlabeled CO2. After the chase period, very little label remained in the ionic fractions (presumed to be mostly C reduction and C oxidation cycle intermediates and amino acids) except at low CO2 partial pressure. Most label was found in the neutral, alcohol soluble fraction (presumed sucrose) or in the insoluble fraction digestable by amyloglucosidase. Sucrose formation was linearly related to assimilation rate (slope = 0.35). Starch formation increased linearly with assimilation rate (slope = 0.56) but did not occur if the assimilation rate was < 4 .mu.mol m-2 s-1. Neither abscisic acid, nor high CO2 in combination with low O2 (thought to disrupt control of C metabolism) caused significant perturbations of the sucrose/starch formation ratio. The pathways for starch and sucrose synthesis are both apparently controlled by the rate of net CO2 assimilation, with sucrose the preferred product at very low assimilation rates.