Accumulation of free proline and glycine betaine in Aster tripolium subjected to a saline shock: A kinetic study related to light period

Abstract

On transferring three‐week‐old plants of Aster tripolium L. growing in a half strength Hoagland's medium to the same medium containing 333 mM NaCl a very quick uptake of salt and, after a lag phase of 3 to 5 h, an increase in free proline level was observed. During the time course of imino acid storage, the accumulation rates were higher in the light than in the dark, thereby suggesting some kind of photocontrol on solute metabolism. At zero time, high levels of glycine betaine were present in young plants grown without salt. However, after the application of saline shock, the betaine level also increased significantly. The highest rate of betaine accumulation was detected during the third day of treatment when the rate of proline storage decreased. Glycine betaine storage could also be linked to light dependent processes; whatever its importance in response to salt shock was, the levels observed were lower than those of plants directly grown on 333 mM NaCl for three weeks. When saline stressed plants were transferred to a medium without NaCl, the proline level quickly decreaed while that of glycine betaine remained stable.