Interaction between ethylene and ABA in the regulation of polyamine level in Arabidopsis thaliana during UV-B stress

The effects of treatment with ethylene (0.01-100 mu l/l) on ABA and polyamine contents and treatment with ABA on ethylene synthesis, polyamines content, and the resistance to UV-B radiation of two-week-old Arabidopsis thaliana (L.) Heynh, Columbia ecotype plants grown uaS < er sterile conditions were studied. Ethylene stimulated the accumulation of polyamines only at concentrations of 0.1-10 mu l/l, which could activate ABA synthesis. Treatment with ABA (50-5000 mu M, 1 mu l per plant) decreased the UV-B-induced ethylene synthesis and a spermine and spermidine loss, increasing the content of putrescine, the precursor of these polyamines. ABA inhibited fresh weight accumulation in irradiated and nonirradiated plants but prevented them from severe damage and death at the high (18 kJ/m(2)) and lethal (27 kJ/m(2)) UV-B dose, respectively. The data obtained demonstrated a mutual regulation of ethylene and ABA syntheses and the participation of these hormones in the control of the polyamine level during adaptation of A. thaliana to UV-B stress.