SHORT-TERM COMPETITION FOR PHOSPHATE BETWEEN 2 GENOTYPES OF ARABIDOPSIS-THALIANA (L) HEYNH

Seedlings from two genotypes of Arabidopsis thaliana (L.) Heynh. that had similar uptake kinetics for inorganic phosphate (P(i)), but differed in the levels to which they could deplete P(i) from solution (different C(min) values), were placed together for 21 h in the absence of exogenous P(i) to determine the effect of differences in C(min) on short-term competition for P(i) as reflected by the movement of the phosphate isotope, P-32. P(i)-starved seedlings were grown at two photon flux densities (30 and 90-mu-mol m-2 s-1). Genotype LC (with the lower C(min)) was better able to deplete a 2.5-mu-M P(i) solution than genotype HC. We predicted that when placed together in a P(i)-free solution, the C(min) differences between the genotypes would result in a continual transfer of P(i) from genotype HC to LC. This did not occur, since genotypes LC and HC did not differ in the proportion of P-32 obtained from labelled HC seedlings. However, LC obtained 1.3 times more P-32 from HC than HC obtained from LC, for seedlings grown at both the lower (P < 0.05) and the higher (P < 0.001) photon flux densities. Differences in C(min) between the genotypes were more pronounced for seedlings grown at the higher photon flux density. Here, genotype LC obtained significantly more P-32 from genotype HC than it did from seedlings of its own genotype (P < 0.001). Genotype HC obtained less P-32 from seedlings LC than it did from those of its own genotype, for seedlings grown at both photon flux densities (P < 0.001).