Attenuation of phosphate starvation responses by phosphite in arabidopsis

When inorganic phosphate is limiting, Arabidopsis has the facultative abili ty to metabolize exogenous nucleic acid substrates, which we utilized previ ously to identify insensitive phosphate starvation response mutants in a co nditional genetic screen. In this study, we examined the effect of the phos phate analog, phosphite (Phi), on molecular and morphological responses to phosphate starvation. Phi significantly inhibited plant growth on phosphate -sufficient (2 mm) and nucleic acid-containing (2 mm phosphorus) media at c oncentrations higher than 2.5 mm. However, with respect to suppressing typi cal responses to phosphate limitation, Phi effects were very similar to tho se of phosphate. Phosphate starvation responses, which we examined and foun d to be almost identically affected by both anions, included changes in: (a ) the root-to-shoot ratio; (b) root hair formation; (c) anthocyanin accumul ation; (d) the activities of phosphate starvation-inducible nucleolytic enz ymes, including ribonuclease, phosphodiesterase, and acid phosphatase; and (e) steady-state mRNA levels of phosphate starvation-inducible genes. It is important that induction of primary auxin response genes by indole-3-aceti c acid in the presence of growth-inhibitory Phi concentrations suggests tha t Phi selectively inhibits phosphate starvation responses. Thus, the use of Phi may allow further dissection of phosphate signaling by genetic selecti on for constitutive phosphate. starvation response mutants on media contain ing organophosphates as the only source of phosphorus.