XVI International Botanical Congess

Under water deficits, root growth is less inhibited than shoot growth. ABA accumulation is often proposed to function in growth regulation, particularly shoot inhibition. This is being assessed using mutants and inhibitors to decrease ABA levels. In water-stressed maize seedlings, ABA 1) maintains root growth by resticting ethylene production (and, perhaps, sensitivity), and 2) can inhibit or promote shoot growth depending on the response to ethylene. In ABA-deficient tomato mutants, shoot growth is inhibited in well-watered plants in the absence of wilting, and is substantially restored by inhibiting ethylene action. Studies of water-stressed plants are in progress. In Arabidopsis, double mutants have been generated to confirm the interaction of ABA and ethylene in growth regulation.