Response to phosphate deficiency in bean (Phaseolus vulgaris L.) roots. Respiratory metabolism, sugar localization and changes in ultrastructure of bean root cells

Bean plants (Phaseolus vulgaris L. 'Zlota Saxa') were cultured on complete (+P) or phosphate-deficient (-P) nutrient medium. A large increase in gluco se concentration was found in the meristematic zone of -P roots compared to control roots. The increased glucose concentration in the meristematic zon e did not influence total respiration rate. Glucose or uncoupler (carbonyl cyanide m-chlorophenylhydrazone) failed to increase the respiration rate in -P root segments, but stimulated respiration in + P roots. The ultrastruct ure of cortical cells from the meristematic root zone showed marked differe nces between +P and -P plants. Large vacuoles, invaginations of the plasmal emma and condensed forms of mitochondria were dominating features in cortic al cells of -P roots. Analysis of extracts after treating roots with dimeth ylsulfoxide (DMSO) indicated different localization of sugars in the cell c ompartments. In roots of -P plants, most of the reducing sugars were detect ed in the cytoplasm fraction while most sucrose was in the vacuole. Observa tions of the effect of 10% DMSO on cell ultrastructure indicated partial de struction of the plasmalemma but not the tonoplast. The localization of red ucing sugars in secondary vacuoles or plasmalemma invaginations in the cell s from the meristematic region of -P roots is discussed. (C) 1998 Annals of Botany Company.