Abstract: The cambium of Eucommia ulmoides Oliv resumed its activities in mid-March. It ceased to produce new phoem cells at the end of July, but continued to differentiate into xylem cells until mid-August, at which time the cambium became dormant albeit subsequent differentiation of newly formed immature phloem and xylem cells into mature ones continued until December. In consistent with the periodicity of cambial activity, the variability of peroxidase isozyme activity as demonstrated by isozymography was most significant in the cambial region. PO I and PO II presented only in the spring when cambium activity was resumed. The activity of PO III was weakened in summer and increased gradually reaching to the highest level in winter. The variability of esterase isozyme activity in the vascular tissues was in consistent with the periodicity of cambial activity. Isozyme bands of EST III-V near the negative pole of the zymograph disappeared in specimens collected during growth season and its activity was revived when cambium became dormant. Isozymes of EST II being the most active and present over time, might play an important role in devolopment and differentiation of vascular tissues.

Key words: Eucommia ulmoides Oliv, periodicity of cambial activity, peroxidase isozyme, esterase isozyme

摘要： 杜仲(Eucommia ulmoides Oliv.)形成层3月中旬恢复活动，7月下旬形成层细胞停止分裂，同时停止产生新的韧皮部细胞，但直到8月中旬才停止产生新的木质部细胞。12新形成的未成熟韧皮部和木质部细胞都继续分化、成熟。形成层活动周期中，过氧化物酶同工酶的酶谱和酶活性在形成层区域和木质部区域中变化最大。POⅠ和POⅡ组同工酶只在春季形成层恢复活动时期存在。POⅢ的酶活性在夏季减弱，而冬季达到最高水平。酯酶同工酶的酶谱和酶活性亦随形成层的活动状态发生变化。负极端的ESTⅢ～Ⅴ组酯酶同工酶在生长季节消失，当形成层休眠时又重出现。ESTⅡ的酶活性最强并在各个时期均存在，它在维管组织的发育分化中可能起重要作用。

关键词: 杜仲, 形成层活动周期, 过氧化物酶同工酶, 酯酶同工酶