The role of Pirecycling processes during photosynthesis in phosphate-deficient bean plants

Bean plants (Phaseolus vulgaris L. cv. Zlota Saxa) were grown on complete (control plants) and phosphate-deficient (low-P plants) culture solutions for 17 d. Phosphate deficiency markedly reduced leaf growth, but only slightly decreased the photosynthesis rate. The intensity of reactions releasing inorganic ortho-phosphate during photosynthesis was examined. In the leaves of low-P plants the pools of photorespiratory metabolites (glycolate and glycine+serine) were markedly increased. At the same time synthesis of soluble sugars from intermediates of glycolic acid cycle was probably enhanced. In low-P leaves the phosphoenolpyruvate carboxylase activity and malate synthesis were increased. Phosphoenolpyruvate and malate were effectively used for amino acid synthesis. Both aspartate and alanine accumulation was twice higher in low-P leaves. It was found that no enhancement in starch and sucrose synthesis rate takes place in phosphate deficient bean leaves. Modifications of photosynthetic metabolism observed under moderate phosphate deficiency facilitate plants acclimation to low-P conditions by enhancement of P1 recirculation during glycolic and phosphoenolpyruvate metabolism.