ABSCISIC-ACID AND ETHYLENE IN MUTANTS OF ARABIDOPSIS-THALIANA DIFFERING IN THEIR RESISTANCE TO ULTRAVIOLET (UV-B) RADIATION STRESS

The effects of ultraviolet irradiation (between 280 and 320 nm) on pla nt survival, ethylene evolution, and abscisic acid (ABA) content were studied in Arabidopsis thaliana (L.) Heunh. plants. Three genetic line s of Arabidopsis differing in their resistance to ultraviolet (UV-B) r adiation stress were used. UV-B irradiation had detrimental effects on plant survival, enhanced ethylene evolution, and increased ABA conten t in the plants of all three lines. The higher ultraviolet dose was ab sorbed, the less was the number of surviving plants and the higher wer e the levels of both phytohormones. The maximum ethylene evolution occ urred during the initial two to four hours after irradiation, but the ABA content peaked only after 24 h. The most resistant line showed the highest ABA content and the fastest ethylene evolution, whereas, in t he susceptible line, both indices were the lowest. After UV-B treatmen t, the ABA-deficient Arabidopsis mutant evolved four to six times more ethylene than the plants with normal ABA content. Stress ethylene pro duction evidently did not depend on the level of endogenous ABA as the kinetics of ethylene evolution was similar in the ABA-deficient mutan t and in other studied Arabidopsis lines.