Abstract: Abstract: 【Objective】To study the dynamics of enzyme activities, which play important roles during cotton fiber development, and its relationship with fiber strength, and provide studying basis for the ways of physiological adjusting to improve fiber strength, 【Method】field experiments were carried out in Nanjing, Jiangsu Province (the Yangtze River region in China) in 2004 and 2005 by choosing three genotype cottons with significant differences in fiber strength as materials. The study focused on the time course of sucrose synthetase, β-1,3-glucanase, peroxidase and IAA oxidase activities during the secondary wall thickening in cotton fiber. The boll samples were collected from the first and second fruiting positions of 6 to 8 sympodial branchs. 【Result】The results showed that β-1,3-glucanase activity continuously decreased during the secondary wall thickening in cotton fiber. The activity curves of other enzymes (sucrose synthetase, peroxidase and IAA oxidase) were all unimodal and they might have a certain synergistic effect during fiber thickening development. However, there were obviously differences among three genotypes in the levels of enzyme activities and occurrence time of the peak. The cultivar (Kemian 1), which produced high strength fiber, had higher peak value of the related enzyme (sucrose synthetase, β-1,3-glucanase, peroxidase and IAA oxidase) activities, and slower descend trend subsequently. These resulted in a longer and more tempered cellulose accumulation, and in the wider range and longer period of fiber strength increase. While the cultivars (Dexiamian 1 and Sumian 15), which produced lower strength fibers, the items were just the contrary. And the cultivar (NuCOTN 33B), which produced medium strength fiber, the items were intervenient.【Conclusion】There are significant differences in the related enzymes activities among different genotypes. And that may be one of important factors which lead to the great difference in the characteristics of cellulose accumulation and the fiber strength formation in different genotype cottons.

Key words: cotton genotype, cotton fiber development, related enzymes, fiber strength