CHANGES IN CARBOHYDRATE CONCENTRATION IN LEAVES, PODS AND SEEDS OF DRY BEAN PLANTS UNDER DROUGHT STRESS

Changes in the concentration of sucrose, glucose, fructose and starch, in leaves, seeds and pods of Phaseolus vulgaris L. cv 'Otomi' of determinate growth habit, were evaluated under both drought stress and non stress (irrigated) conditions. Plants were submitted to drought stress during the flowering, pod formation and seed filling stages. The stress increased the concentrations of glucose from 18 up to 196% and of fructose from 20 up to 333% in mature leaves, likely due to starch hydrolysis, while showing starch reductions from 17 up to 46% and sucrose reductions from 41 up to 70%. These changes in leaves promoted the sugar exports toward pods and seeds, since their sucrose concentration increased. In the reproductive organs, the concentration of glucose and fructose of stressed plants increased 136 and 138% in pods and 83 and 73% in seeds, respectively. Contrary to the changes registered in leaves, in reproductive tissues the sucrose increased up to 238% in pods and up to 148% in seeds, while the starch became reduced down to 37% in pods and to 21% in seeds. The increase of hexoses in pods and seeds might be explained by in situ starch hydrolysis, whereas the increase in sucrose is probably due to an enhanced synthesis of this sugar for a higher osmotic adjustment.