Abstract: Taking two cotton cultivars with different temperature-sensitivity during their fiber strength formation as test materials, a field experiment of different sowing dates was conducted in Nanjing of Jiangsu Province in 2006 and 2007 to study the effects of low temperature on the activities and gene expression of the enzymes related to fiber development. The low temperature induced by late sowing (with the mean daily minimum temperature being 211, 205, and 181 ℃ during fiber development period) had definite effects on the enzyme activities, and accordingly, the fiber strength formation. Low temperature increased the invertase and β-1,3-glucanase activities, decreased the sucrose synthase and sucrose phosphate synthase activities, prolonged the time with higher gene expression level of Expansin and sucrose synthase, and delayed the expression peak and decreased the gene expression quantity of β-1,3-glucanase. There existed significant differences in the low-temperature responses of related enzymes activities between the two cultivars, with the change ranges of the enzyme activities being larger for temperature-sensitive cultivar Sumian 15 than for temperature-insensitive cultivar Kemian 1, which could be the main reasons leading to the different temperature-sensitivity of the two cotton cultivars during their fiber strength formation.

Key words: cotton fiber, temperature-sensitivity, enzyme activity, gene expression, fiber strength, desert shrub, projective cover, biomass, aggregation intensity, coefficient of variation.