Abstract: In this paper the potted seedlings of Pinus sylvestris var. mongolica Litv. were treated by soil drought stress to study the activity levels of SOD, MDA content, the composition of membrane fatty acids and the amount of ethylene release of needles. The results showed that the SOD activity levels first increased and then decreased with the aggravating of drought stress; The change trends of MDA content was to increase to the highest level, and then decrease to a still high level; IUFA started to decrease under serious stress; Ethylene released obviously when the IUFA level dropped drastically, at the same time the seedlings began to die. These results show that be the drought stress damage of needles of Pinus sylvestris var. mongolica Litv. is caused by membrane-lipid peroxidation; the increase of MDA content aggravates peroxidation, which causes the obvious decrease of IUFA level and ethylene evolution, and then seedlings begin to die.

Key words: Drought stress, Membrane lipid peroxidation, Ethylene, Index of unsaturation fatty acid(IUFA)