Abstract:

High temperature is a key factor during wheat grain filling affecting grain yield and quality in main production areas of China, but the physiological mechanism of quality formation related to high temperature stress remains unclear. The experiments were carried out in growth chambers to investigate the effects of high temperature conditions during grain filling on the formation of total starch, amylopectin and amylose, and the activities related to starch synthesis using two wheat cultivars including Yangmai 9 with low grain protein content and Xuzhou 26 with high grain protein content. Four day/night temperature regimes of 34℃/22℃, 32℃/24℃, 26℃/14℃ and 24℃/16℃ from 7 days after anthesis until maturity were established, which included two daily average temperatures 28℃ and 20℃, and two day-night temperature differences 12℃and 8℃. The results showed that the contents of total starch and amylopectin were markedly reduced, but amylose content was slightly affected (Fig.1, Fig.2, Fig.3 and Table 1), and the ratio of amylopectin to amylose was reduced significantly in higher temperature treatments. During the early period of grain filling, the activities of key enzymes such as sucrose synthase (SS) and granule-bound starch synthase (GBSS) were enhanced, but the activities of SS, GBSS and soluble starch synthase (SSS) during the late period of grain filling were decreased in high temperature treatments (Fig.4, 6, 7). GBSS activity was increased in Yangmai 9, and SSS activity was decreased in Xuzhou26 during early period of grain filling under high temperatures (Fig. 6,7), indicating the different enzymology mechanism in two wheat cultivars. In addition, under high temperatures, grain starch content was similar between two treatments with day-night temperature differences in two wheat cultivars. Under optimum temperatures, grain starch content was higher in the treatment of 26℃/14℃(Fig. 1). Moreover, under high temperatures, SS activity was higher in the treatment of 34℃/22℃ during the middle and late period of grain filling, whereas the activities of SSS and GBSS were higher under 32℃/24℃ (Fig. 4, 6, 7). Under optimum temperatures, the activities of three key enzymes were higher in the treatment with higher day-night temperature difference (26℃/14℃). The above results indicated that starch synthesis was affected more by temperature levels than by day-night temperature differences.

Key words: Wheat, High temperature, Starch, Starch synthase, Sucrose synthase