Compartmentation and fluxes of sugars in roots of Phaseolus vulgaris underphosphate deficiency

The influence of phosphate deficiency on the sugar accumulation and sugar p artitioning in the root cells of bean (Phaseolus vulgaris L,) was studied. Bean plants were cultured 17 - 19 d on a phosphate-sufficient and phosphate -deficient nutrient medium. Phosphate deficit in the growth medium resulted in increased sugar concentration for about 30 % in the apoplastic and cyto plasmic compartments as well as in the vacuoles of root cells. However, the distribution of sugars between apoplast and cytoplasm compartment and vacu ole was not affected by decreased phosphate concentration. About 20 % of su gars were found in the apoplast and cytoplasm, about 80 % in the vacuole, L ow phosphate concentration enhanced influx of exogenous C-14-sucrose into m eristematic and elongation zones of root. The C-14-labelled sugar content i n the root tips increased for about 60 % as compared to control plants. Pho sphate deficiency increased also C-14-glucose uptake and content in the roo t tips. However, the amount of (CO2)-C-14 liberated during respiration of P -deficient roots (after feeding with uniformly labelled C-14-glucose) was l ower than (CO2)-C-14 respired by control plants, thus a large part of accum ulated sugars seems to be metabolically inactive.