The studies on leave protein of Betula platyphylla seedlings by the methods of SDS PAGE electrophoresis and dimensional gel electrophoresis was concerned. The result indicated that some new proteins such as 29kD pI4 3, 29kD pI4 2, 14kD pI5 3 and 11 5kD pI5 16 protein point were induced by soil drought stress, and some protein disappeared, for instance four protein between 12 4～11 5kD pI5 8～6 44 in seedlings leaves of B. platyphylla during soil drought stress.
The active oxygen content, MDA content and electrolyte leakage in the leaves of Betula platyphylla seedlings increased under the soil drought stress. Activity of cell defense enzymes changed markedly when the stress of draught was intensified. SOD activity increased then decreased, POD activity decreased and CAT activity decreased then increased. All above physiological index returned to approach the normal level before stress after the water of soil was recovered.
