Accumulation of Proline and Sucrose during the First Hours after Transfer of Chlorella emevsonii to High NaCl

Abstract

Net synthesis of proline, the main osmotic solute in C. emersonii, showed a lag of at least 15 min following transfer of cells from 1 m~ NaCl to concentrations ranging between 25 and 335 m~ NaCl. During the subsequent period of rapid net proline synthesis, the maximum rates were approximately linearly related to the decreases in external osmotic potential (YJ until the cells plasmolysed. Beyond the point of incipient plasmolysis, further large decreases in Y* did not change the maximum rates of proline synthesis. The steady-state levels of proline were lower, and were reached faster, the smaller the decreases in external Ys. Overall these results support the notion that turgor potential has a regulating role in the synthesis of osmotic solutes. Sucrose synthesis showed no lag and was rapid even in plasmolysed cells. Cycloheximide inhibited formation of proline but not of sucrose. This, together with the lag phase of 15 min in proline synthesis, indicated that transfer of C. emersonii to high NaCl induced de novo synthesis of enzymes involved in proline formation. Effects of DCMU and darkness were also measured. Cells transferred to 125 m~ NaCl still showed substantial net synthesis of sucrose, but not of proline. Supply of glucose in the dark did not lead to proline formation, but it did stimulate proline synthesis which occurred when glutamate was supplied.