INTERACTION BETWEEN HEAT-SHOCK AND WATER-STRESS IN PLANTS .2. OSMOREGULATION IN THE LEAVES OF COTTON PLANTS SUCCESSIVELY TREATED WITH SHORT-TERM HYPERTHERMIA AND SOIL DROUGHT

Adaptation of cotton (Gossypium hirsutum L.) plants to successive trea tment by heat shock and soil drought was studied. Osmoregulation in pl ants exposed to long-term soil drought or long-term soil drought prece ded by short-term hyperthermia (45 degrees C for 1.5 h) was compared w ith osmoregulation in plants grown in a greenhouse at a normal water s upply (control plants). After watering was ceased, the soil moisture c ontent decreased from 70 to 20% of field moisture capacity, while the leaf cell sap osmotic pressure almost doubled, irrespective of plant p retreatment by hyperthermia. Amino acids and amides were the only cell sap components among all the studied compounds (ions, sugars, free am ino acids, and amides) whose contribution to an increase in osmotic pr essure was proven. By the end of the drought period (40 days without w atering), their contribution was 5-7 times higher than in the untreate d (control) plants. This increase was most pronounced in the cell sap of the heat-shock pretreated plants. The maximum enhancement was found for arginine, proline, and asparagine (by factors of 240, 170, and 14 0, respectively). The ability of heat-shock pretreatment to stimulate amino acid and amide accumulation during the subsequent period of soil drought suggests that the systems responsible for their accumulation are of great importance for plant adaptation both to water deficit alo ne and to the combined effect of heat shock and water deficit.