Sucrose metabolism in cotton (Gossypium hirsutum L.) fibre under low temperature during fibre development

The effects of low temperature on sucrose content and activities of key enzymes related to sucrose metabolism in cotton (Gossypium hirsutum L.) fibre were investigated. Two cotton cultivars, Kemian 1 and Sumian 15, were grown in the field at two sowing dates in 2006 and three sowing dates in 2007, the differences of environmental conditions during fibre development period (from flowering date to boll opening date) for different sowing dates were primarily on temperature. Low temperatures (MDTmin of 21.1, 20.5 and 18.1°C) in late sowing dates (25 May/10 June) prolonged the fibre development period, and had significant effect on cellulose synthesis and sucrose metabolism. Results showed that, under low temperature, sucrose content was increased, cellulose content and sucrose transformation rate were decreased, and the variability of cellulose content and sucrose transformation rate through sowing dates in Sumian 15 was more than that in Kemian 1. The measurable activities of sucrose phosphate synthase (SPS), sucrose synthase (SuSy) and acid/alkaline invertases in sucrose metabolism were affected by low temperatures. Under low temperatures, activities of SuSy and invertase in sucrose degradation were increased, and two cultivars had the similar change. In contrast, the activity of SPS in sucrose synthesis was lower than the activity in developing fibre at normal environmental condition, and the time to peak activity was delayed, SPS activity in response to temperatures differed between two cultivars. The results indicated that restrained cellulose synthesis and sucrose metabolism under low temperature were mainly attributed to the changed activities of enzymes (SPS, SuSy and invertase), and the difference of cellulose synthesis and sucrose metabolism in response to temperature in fibre cells for two cotton cultivars was mainly determined by the level of SPS activity.