Effect of ABA on the UV-B-Induced ethylene evolution by the etr and ctr mutants of Arabidopsis thaliana

The responses of 14-day-old Arabidopsis thaliana (L.) Heynh. plants to UV-B irradiation (280-320 nm) and ABA treatment were investigated. Wild-type plants as well as ethylene-insensitive etr1-1 and ctr1-1 mutants were used. The etr1-1 mutant considerably differed from the ctr1-1 one in the fresh weight production after UV-B treatment (29.5 kJ/m(2)). The irradiated etr1-1 plants fell well behind the nonirradiated ones during the first two days after stress, but by the 8th day, their weight attained 70% of control plant weight. In contrast, Ctr1-1 mutant weight comprised 70% of control level after two days of stress but, by the 8th day, it was only 56% of the weight of control plants. In wild-type and ctr1-1 plants, ABA, in the 8 x 10(-6) to 2 x 10(-4) M concentration range, increased the difference between the weights of nonirradiated and irradiated plants, but in etr1-1 plants. ABA decreased this difference. The etr1-1 ctr1-1, and wild-type plants were very similar in the dynamics of ethylene evolution after UV-B treatment (7.4 kJ/m(2)). In wild-type, etr1-1, and ctr1-1 plants, ABA, in a concentration-dependent manner, inhibited UV-B-induced ethylene evolution to the same extent. The results obtained show that ABA exerted an opposite effect on UV-B-dependent growth in the plants with active (wild type and ctr1-1) and blocked (etr1-1) ethylene signal pathway, whereas the inhibition of ethylene synthesis by ABA was not related to ethylene signal transmission.