Activity Changes of Enzymes Associated with Fiber Development and Relationship with Fiber Specific Strength in Two Cotton Cultivars

Sucrose synthase (SuSy) and β-1,3-glucanase play very important roles in developing cotton (Gossypium hirsutum L.) fiber. To investigate the characteristics of Susy and β-1,3-glucanase, as well as the expressions of related genes, 2 cotton cultivars, Kemian 1 with high strength fiber of 35 cN tex−1 and Dexiamian 1 with low strength fiber of 26 cN tex−1, were used. The differences of the cellulose deposition and fiber specific strength in the 2 cultivars were related to the levels of key enzyme activities and the gene expression. The activity and gene expression of sucrose synthase and β-1,3-glucanase were higher in Kemian 1 than those in Dexiamian 1. The expression of SuSy gene was obviously higher in Kemian 1 than that in Dexiamian 1 at 25 days post anthesis (DPA), whereas the expression of β-1,3-glucanase was obviously different at 10–25 DPA between the 2 cultivars. During the accumulation of cellulose, Kemian 1 had a longer period and a gentler speed accumulation than Dexiamian 1. The position of fruiting branch also affected the accumulation of cellulose. Genes for Expansin, β-1,4-glucanase expressed lower when the boll age increased, and showed significant decrease at 20 DPA. This was in agreement with the dynamic change during the cotton fiber development that is the fiber length elongated rapidly before 25 DPA, and slowed down until it almost stopped thereafter. From the results, it is suggested that the different characteristics of key enzymes activity in fibers may cause the differences in the cellulose accumulation and fiber-specific strength.