INVOLVEMENT OF ABSCISIC-ACID IN PHOTOSYNTHETIC PROCESS IN HORDEUM-VULGARE L DURING SALINITY STRESS

In Hordeum vulgare L. plants, NaCl stress imposed through the root med ium for a period of 8 days decreased the rate of CO2 assimilation, the chlorophyll and protein leaf content, and the activity of ribulose-1, 5-bisphosphate carboxylase. The activity of phosphoenolpyruvate carbox ylase was twofold over the control. Pretreatment with abscisic acid (A BA) for 3 days before salinization diminished the inhibitory effect of NaCl on the rate of CO2 fixation. The leaf Na+ and Cl- content decrea sed in ABA-pretreated plants. Both ABA and NaCl treatments led to an i ncrease in the endogenous level of ABA in the plant leaves. Patterns o f total proteins extracted from the leaves of control or ABA- and salt -treated plants were compared. Both ABA and NaCl induced marked quanti tative and qualitative changes in the polypeptide profiles concerning mainly the proteins with approximately equal mobility. The results are discussed in terms of a possible role of ABA in increasing the salt t olerance when ABA is applied to the plants for a short period before e xposure to salinity stress, thus improving the invulnerability to unfa vorable conditions.