Physiological Mechanisms Of Stylosanthes Utilizing Exogenous Organic Phosphorus

Stylo(Stylosanthes spp.) is a dominating leguminous pasture widely grown in tropical and subtropical regions, which are mostly acid soils. However, phosphate (Pi) is easily fixed by soil particles to form potential phosphorus (P) pool, which is not directly utilized by plants on acid soils. Among the phosphorus pool, organic P is20%-80%. Therefore, it is very important to study mechanisms underlying stylo utilization of organic P in order to elucidate adaptive strategies of stylo to acid soil. In the study, two stylo genotypes were used, including TPRC2001-1(P-efficiency genotype) and Fine-stem (P inefficiency genotype). The effects of P availability on root morphology, P content, activities of internal and secreted acid phosphatase (APase), as well as their isofroms were investigated in hydroponic culture. Subsequently, utilization of organic P (phytate and dNTPs) was compared between the two genotypes through solid MS medium culture. The main results were shown as follows:1) Biomass and P content in two stylo genotypes were significantly reduce by Pi starvation in nutrient solution. Furthermore, TPRC2001-1had higher biomass, total P content, total root length, root surface and volume than those in Fine-stem, indicating that TPRC2001-1was a P efficient genotype, while Fine-stem was a P inefficient genotype.2) Low P availability enhanced internal and secreted APase activities in both genotypes. Furthermore, internal and secreted APase activities in roots of TPRC2001-1were higher than those in Fine-stem, respectively. It was suggested that increased APase activities might be one of the physiological mechanisms of TPRC2001-1adaptation to P deficiency.3) APase isoforms in stylo roots were analyzed through polyacrylamide gel electrophoresis. There were four APase isoforms in stylo roots subjected to Pi starvation and all of four isoforms activities were enhanced in both stylo genotypes. Among them, two isoforms activities of TPRC2001-1was apparently higher than Fine-stem. It was suggested that Pi starvation increased APase activities were mainly contributed by increased activities of pre-existing isoforms, and there were genotypic variations in APase isoforms activities of stylo roots.4) Capability of stylo to utilize organic P was evaluated in the solid medium supplied with phytate and dNTPs. Compared to plants grown without P application, increased biomass and total P content was only observed in TPRC2001-1, not in Fine-stem by application of200μM phytate and250μM dNTPs, indicating that TPRC2001-1exhibit superior capacity to utilize exogenous organic P. Taken together, one of physiological mechanisms underlying higher P efficiency in TPRC2001-1is higher secreted APase activities and capability to utilize organic P.