Phosphate Turnover in Various Parts of Nodulated Soybean (Glycine max (L.) Merr.) Plants and the Relation to the Xylem Transport

Phosphorus is a major essential element in plants, and the absorption and transport of P are related to crop growth and productivity. Phosphate (Pi) is absorbed in the roots and transported to the shoot. Plants store surplus Pi in the vacuoles. The characteristics of Pi storage and turnover in various parts of the nodulated soybeans might be related to plant growth and P-use efficiency. This research focused on the changes in the Pi concentrations and Pi contents in each part of young soybean plants grown in Pi-sufficient (50 μM Pi) or Pi-deficient (0 μM Pi) conditions. Also, the Pi flux rate in xylem sap from roots to shoot was determined. The growth of the plants was the same after 7 days of Pi-sufficient and Pi-deficient treatments. During the Pi-deficient period, the Pi concentrations in the roots, leaves, and stems decreased significantly but did not deplete. The decrease in Pi concentration in nodules was much slower than the other parts. After the re-supply of 50 μM Pi in the solution, the Pi concentration increased only a little in each part of the Pi-deficient plants. The Pi concentration and Pi flux in the xylem sap quickly responded to the changes in the Pi concentration in the culture solution.