Abstract: In slow soil-drought treatment (T1) lipoxygenase (LOX) activity increased, whereas ethylene, ethane and 1-aminocyclopropane-l-carboxylic acid(ACC) levels revealed little change. In leaves of soybean (Glycine max (L.) Merr. ) plants in pots. In rapid soildrought treatment (T2), ethylene and ACC levels and LOX activity increased rapidly at first and then declined later. Ethane production increased markedly when the leaf membrane damage was more than 60% when the detached leaves were exposed to dry air (T3), changes of ethylene, ethane and ACC levels and LOX activity followed the same patterns as those in rapid soil-drought treatment. There was a positive correlation between LOX activity and ethylene production in both T2 and T3. Increased free fatty acids were observed in all treatments. In addition, pretreatment of detached leaves with free redical scavengers before desiccation resulted in the inhibition of LOX activity and ethylene formation to the same extent, but enhancement of ethane production. The results suggested that the stimulation of LOX-catalysed oxidation of polyunsaturated fatty acids leads to an increased stress of ethylene production from ACC. In leaves with high membrane damage, there were loss of LOX activity and accumulation of unsaturated fatty acid which lead to ethane synthesis.

Key words: Soybean, Drought, Lipoxygenase, Ethylene, Ethane, 1-aminocyclopropane-l-carboxylic acid