Molecular size distribution and enzymatic degradation of organic phosphorus in root exudates of spring barley

摘要

Seeds from two varieties of spring barley (Prisma and Camorgue) were grown axenically in water. After 14 days, the culture solutions contained organic P substances (about 4 μg P per plant) derived from root exudation, representing about 3 of the total P found in the seed. Gel filtration, separated the organic P into two well defined peaks, one with a high molecular weight (>45000 daltons) and the other with a low molecular weight (<500 daltons). The bioavailability of the soluble organic P released was assessed enzymatically and chemically. At the optimum pH of 5.0, phytase and acid phosphatase hydrolysed about 80 and 65, respectively of the organic P in the exudate after 24 h whereas at the optimum pH of 9.8, alkaline phosphatase hydrolysed up to 40 P after the same length of time. In a pH 5.0 buffer, up to 10 of the organic P was hydrolysed compared with up to 45 in a pH 9.8 buffer. The high molecular weight organic P fraction recovered from the G-75 Sephadex behaved similarly