Sucrose Metabolism in Leaves and Roots of Bean (Phaseolus vulgaris L.) during Phosphate Deficiency

The influence of phosphate deficiency on the accumulation and metabolism of sugars in the source and sink leaves and roots of bean (Phaseolus vulgaris L.) was studied after 16 days of plant culture. Glucose, sucrose and starch contents increased in all tissues of phosphate-deficient plants as compared with control plants. Phosphate deficiency increased activities of enzymes involved in sucrose synthesis in the leaves and root; sucrose phosphate synthase (EC 2.4.1.14) activity increased about twice, while sucrose synthase (EC 2.4.1.13) activity increased about 3-fold in the mature leaves and 50% and 90% in the young leaves and roots, respectively. Phosphate deficiency also increased the activities of enzymes hydrolyzing sucrose in the leaves and roots; neutral invertase (EC 3.2.1.26) activity increased twice in the source leaves and about 50% in sink leaves and roots. Acid invertases (EC 3.2.1.26) were divided into soluble and insoluble forms; insoluble invertases activities were several times lower than those of soluble invertases, both in the leaves and roots. Pi starvation increased mainly the activities of insoluble forms of acid invertases in all tissues in bean plants.