Abstract
Phosphorus is one of the most critical macronutrients for plants and is taken up from the soil in the form of phosphate (H2PO4 −, Pi). It is frequently not readily available to plants as it is often found in low concentrations and bound to other soil components. Hence plants have developed strategies to adjust to Pi starvation with adaptations such as alterations of primary root length, number of lateral roots or secretion of organic acids to raise Pi uptake capacity. In addition, Pi depleted plants increase the expression of genes involved in Pi acquisition, e.g. Pi transporters and purple acid phosphatases. Phosphite (H2PO3 −, Phi) is the more reduced form of Pi and taken up by plants through phosphate transporters. Although metabolically inert, Phi is able to suppress Pi starvation responses, which results in an exacerbated Pi depletion leading to an inhibition of plant growth. In addition, Phi accumulation can lead to toxicity, likely through interference with Pi dependent reactions or remobilization. Phi is also used as an inducer of plant defense and biostat against plant pathogens, especially oomycetes (e.g. Phytophthora spp.), which have devastating effects in horticultural and native ecosystems. The only reliable measure to control these pathogens is Phi, but its mode of action is yet to be elucidated. To gain a better understanding on the effects of Phi on plant growth and defense we have started to investigate the natural genetic variation of Phi sensitivity in Arabidopsis thaliana. Findings from this research will improve our knowledge of the mode of action of Phi on plant defense responses, and might also have implications for the understanding of Pi signaling or metabolism. Investigations into the genetic background of Phi dependent adaptation have been made by observing the phenotypic responses of 18 different Arabidopsis accessions. We will present first results obtained by screening for root phenotypes on media containing varying ratios of Pi and Phi.