MOLECULAR-SIZE DISTRIBUTION AND ENZYMATIC DEGRADATION OF ORGANIC PHOSPHORUS IN ROOT EXUDATES OF SPRING BARLEY

Seeds from two varieties of spring barley (Prisma and Camorgue) were g rown axenically in water. After 14 days, the culture solutions contain ed organic P substances (about 4 mug P per plant) derived from root ex udation, representing about 3% of the total P found in the seed. Gel f iltration, separated the organic P into two well defined peaks, one wi th a high molecular weight (> 45 000 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 o ptimum pH of 5.0, phytase and acid phosphatase hydrolysed about 80% an d 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 o rganic P was hydrolysed compared with up to 45% in a pH 9.8 buffer. Th e high molecular weight organic P fraction recovered from the G-75 Sep hadex behaved similarly.