Assimilate translocation in bean plants (Phaseolus vulgaris L) during phosphate deficiency

A rapid decrease in inorganic phosphate content in bean plants (Phaseolus vulgaris L. cv. Zlota Saxa) grown on phosphate deficient medium induced an increased translocation of assimilated carbon from the shoot to the root. The incorporation of (CO2)-C-14 to the leaves of the plants after 16 days of culture on phosphate deficient medium was about 14 % higher than in control plants grown on complete medium. The C-14 labelling in the roots of phosphate deficient plants (-P) was about 100 % higher than in the control (+P). Most of the labelling was found in the water soluble fraction. The water soluble fraction was divided into sugar, amino acid and organic acid fractions. The sugar fraction was the largest fraction and its radioactivity was higher in the roots of phosphate deficient plants than in control roots. The radioactively of amino acid and organic acid fractions was markedly lower in phosphate deficient compared with phosphate sufficient roots. The higher labelling of sugars in -P roots corresponded to the higher content of sucrose and glucose. Rather the higher glucose content in -P roots observed earlier during the culture than the increase in sucrose level suggested the enhanced hydrolysis of transported sucrose. However, the activities of acid and neutral invertases in +P and -P roots were very similar and the differences statistically insignificant. The greater assimilate transport and sugar accumulation in bean roots appears to be the early plant response to phosphate deficiency.