Effects of ABA Application to the Culture Solution on the Growth, Water Relations and Temperature Stress in Tomato Plants.

Effects of abscisic acid (ABA) applied to the culture solution on the growth, water relations and temperature stress in tomato plants were investigated.1. Plant growth was strongly inhibited when plants were placed in culture solutions containing 5 and 10 ppm ABA ; it was slightly promoted in culture solutions of 0.1 ppm ABA primarily because root growth was stimulated.2. ABA suppressed the water absorption by roots and reduced transpirational loss from detached leaves. The leaf temperature of ABA treated plants during the day was several degrees higher than that of untreated ones depending on ABA concentrations. At 0.1 ppm ABA, the a-naphthylamine oxidizing activity of roots and the formation and growth of adventitious roots were enhanced.3. At 0.5 ppm ABA, cold hardiness of tomato seedlings increased with a corresponding smaller loss of water from detached leaves and higher a-naphthylamine oxidizing capacity of roots, as comparison with untreated plants.4. On plants exposed to high temperature, ABA treatments advanced tomato fruit maturity with a concomitant increase in sugar content of fruit. It was obseved that 0.1 ppm ABA treatment tended to increase fruit yield.