Effects of late planting and shading on sucrose metabolism in cotton fiber

Effects of cool temperature due to late planting and low light due to shading on sucrose metabolism in cotton fiber were investigated with two cotton cultivars (Kemian 1, cool temperature-tolerant and Sumian 15, cool temperature-sensitive) at two planting dates (the optimized planting date 25 April and the late planting date 10 June) along with two shading levels of crop relative light rate (CRLR) 100% and 60% in 2010 and 2011. Compared with the optimized planting date with CRLR 100% (OPD), the acid invertase (AI) activity was little affected in the optimized planting date with CRLR 60% (OPD-CRLR 60%). The sucrose synthase (SuSy) and sucrose phosphate synthase (SPS) activities were decreased, which would reduce sucrose degradation and recycle, hindering the synthesis of cellulose. However, the sucrose concentration was decreased, which might be because of lower sucrose import from the leaf. The transcript levels of sucrose synthase gene (Susy) and sucrose phosphate synthase gene (SPS) isoforms were decreased. Comparison between the two cultivars, SPS1 was the largest down-regulated isoforrn in Kemian 1, but SPS2 was the largest down-regulated isoform in Sumian 15. Also, the SPS activity was more sensitive to low light for Kemian 1 than Sumian 15. Although SuSy and AI activities were much. higher in the late planting date with CRLR 100% (LPD) than OPD, sucrose concentration was still high. Therefore, a lot of sucrose could not be fluently used in cellulose synthesis, leading to the decrease of cellulose concentration. The transcript levels of the three SPS isoforms increased for both cultivars. The expressions of SusyA, SusyB, and SusyC were increased for Kemian 1, but the expressions of SusyD, SusyA, SusyB, and SusyC were significantly decreased for Sumian 15. In the late planting date with CRLR 60%, no interaction effect between cool temperature and low light was observed in the concentrations of cellulose and sucrose, the activities of SPS and Al and the expression of SPS3, but was found in the transcript levels of SusyB and SPS2 for both cultivars. Also, the interaction effect was observed in the transcript levels of SusyA, SusyC, SusyD and SPS1 in Sumian 15, but was not found in Kemian 1. (C) 2016 Elsevier B.V. All rights reserved.