ENHANCED RUBBER ACCUMULATION AND RUBBER TRANSFERASE-ACTIVITY IN GUAYULE UNDER WATER-STRESS

Effects of water stress on rubber accumulation and on the activities of rubber transferase (Cis-1,4-polyisoprenyl transferase) were investigated in field-grown guayule (Parthenium argentatum Gray) plants. A pronounced increase in the activities of rubber transferase was recorded in the stressed plants. An increase in enzyme activity was observed with decreased leaf water potential (.psi.) from -0.5 MPa to -2.5 MPa and the activity declined thereafter. The rubber yield (per individual plant and on a per cent dry weight basis) also increased with a decrease in .psi. value upto -2.5 MPa, followed by a sharp decline. Rewatering of the guayule plants increased the .phi. value, followed by a continuous decline in the transferase activity over the next 9 days. The results indicate that maintainance of low leaf water potentials is advantageous for maximized rubber accumulation in guayule. The increased levels of rubber transferase activity during water stress were attributed to a shift in de novo synthesis of the enzyme, resulting altered patterns of rubber accumulation in guayule. The results point to a clear correlation between the ability of guayule to grow in arid areas and its better performance in rubber accumulation under controlled water-stress conditions.