UPTAKE AND TRANSLOCATION OF PHOSPHATE BY PHO2 MUTANT AND WILD-TYPE SEEDLINGS OF ARABIDOPSIS-THALIANA

The pho2 mutant of Arabidopsis thaliana (L.) Heynh. accumulates excess ive Pi (inorganic phosphate) concentrations in shoots compared to wild -type plants (E. Delhaize and P. Randall, 1995, Plant Physiol. 107. 20 7-213). In this study, a series of experiments was conducted to compar e the uptake and translocation of Pi by pho2 with that of wild-type pl ants. The pho2 mutants had about a twofold greater Pi uptake rate than wild-type plants under P-sufficient conditions and a greater proporti on of the Pi taken up accumulated in shoots of pho2. When shoots were removed, the uptake rate by roots was found to be similar for both gen otypes, suggesting that the greater Pi uptake by the intact pho2 mutan t is due to a greater shoot sink for Pi. Although pho2 mutants could r ecycle (32)Pi from shoots to roots through phloem the proportion of (3 2)Pi translocated to roots was less than half of that found in wild-ty pe plants. When transferred from P-suffcient to P-deficient solutions, Pi concentrations in pho2 roots had a similar depletion rate to wild- type roots despite pho2 shoots having a fourfold greater Pi concentrat ion than wild-type shoots throughout the experiment. We suggest that t he pho2 phenotype could result from a partial defect in Pi transport i n the phloem between shoots and roots or from an inability of shoot ce lls to regulate internal Pi concentrations.