Induction of a major leaf acid phosphatase does not confer adaptation to low phosphorus availability in common bean

Acid phosphatase is believed to be important for phosphorus scavenging and remobilization in plants, but its role in plant adaptation to low phosphoru s availability has not been critically evaluated. To address this issue, we compared acid phosphatase activity (APA) in leaves of common bean (Phaseol us vulgaris) in a phosphorus-inefficient genotype (DOR364), a phosphorus-ef ficient genotype (G19833), and their F-5.10 recombinant inbred lines (RILs) . Phosphorus deficiency substantially increased leaf APA, but APA was much higher and more responsive to phosphorus availability in DOR364 than in G19 833. Leaf APA segregated in the RILs, with two discrete groups having eithe r high (mean = 1.71 mu mol/mg protein/min) or low (0.36 mu mol/mg protein/m in) activity. A chi-square test indicated that the observed difference migh t be controlled by a single gene. Non-denaturing protein electrophoresis re vealed that there are four visible isoforms responsible for total APA in co mmon bean, and that the difference in APA between contrasting genotypes cou ld be attributed to the existence of a single major isoform. Qualitative ma pping of the APA trait and quantitative trait loci analysis with molecular markers indicated that a major gene contributing to APA is located on linka ge group B03 of the unified common bean map. This locus was not associated with loci conferring phosphorus acquisition efficiency or phosphorus use ef ficiency. RILs contrasting for APA had similar phosphorus pools in old and young leaves under phosphorus stress, arguing against a role for APA in pho sphorus remobilization. Our results do not support a major role for leaf AP A induction in regulating plant adaptation to phosphorus deficiency.