Sucrose hydrolysis in bean roots (Phaseolus vulgaris L .) under phosphate deficiency

Abstract

Bean plants (Phaseolus vulgaris L .) were cultured for 16 days on phosphate-sufficient (+P) and phosphate deficient (−P) nutrient medium. Phosphate deficiency in the roots increased glucose and sucrose content more in the root tips than in the mature parts of roots and altered the sucrose/glucose ratio. Changes in the sucrose/glucose ratio in roots of −P plants compared with the control plants indicated differences in sucrose metabolism in these roots. Phosphate deficiency increased activities of cytosolic enzymes hydrolysing sucrose in the root tips; sucrose synthase (EC 2.4.1.13) activity increased more than twice, neutral invertase (EC 3.2.1.26) activity about 30%. However the activities of acid invertases (EC 3.2.1.26) in the roots of +P, −P plants were very similar. It is concluded that sucrose synthase have an increased role in sucrose hydrolysis in the growing parts of root under phosphate deficiency conditions. Intensification of sucrose hydrolysis in the cytoplasm may indicate that sucrose unloading from the phloem in bean roots occurs by symplastic route.