Abstract: By the method of hydroponic culture, and taking Cucurbita ficifolia B. as rootstock, this paper studied the effects of grafting on the root polyamine metabolism of cucumber seedlings under copper stress. The results showed that under copper stress, the root activities of cucumber seedlings were inhibited, and electrolyte leakage increased, with these changes being significantly lower for grafted than for ungrafted cucumber seedlings. In addition, the contents of free spermidine and spermine, and of conjugated and bound polyamines were significantly higher in grafted than in ungrafted seedling roots, while the free putrescine content and the ratio of free putrescine to polyamines were on the contrary. Comparing with those in ungrafted cucumber seedlings, the root arginine decarboxylase (ADC), ornithine decarboxylase (ODC), and S-adenosylmethionine decarboxylase (SAMDC) activities in grafted cucumber seedlings were higher, while the diamine oxidase and polyamine oxidase activities were significantly lower. All of these indicated that under copper stress, the synthesis of polyamine in grafted seedling roots was increased, while the degradation of polyamine was decreased, resulting in a higher accumulation of polyamine in the roots, and the increase of the tolerance of cucumber seedlings to copper stress.

Key words: grafting, copper stress, Cucurbita ficifolia B. , polyamine metabolism, three provinces of Northeast China, crop potential yield, potential yield loss rate, climatic resource utilization efficiency.