Effects of high temperature during grain filling on key enzymes involved in starch synthesis in two wheat cultivars with different quality types

Китайский. 以徐州26（高蛋白含量）和扬麦9号（低蛋白含量）2个不同品质类型小麦品种为材料，利用人工气候室模拟小麦花后高温条件，研究了灌浆期高温对籽粒淀粉积累及淀粉合成关键酶活性的影响。结果表明，与适温处理（20℃）相比，高温（28℃）显著降低了籽粒中总淀粉及支链淀粉的含量，而对直链淀粉含量的影响较小，导致支，直链淀粉的比例显著降低。高温提高了灌浆初期小麦籽粒中蔗糖合成酶（SS）和结合态淀粉合成酶（GBSS）活性，但明显降低了灌浆后期SS、GBSS和可溶性淀粉合成酶（SSS）活性。品种问相比，灌浆初期高温处理提高了扬麦9号籽粒GBSS活性，但显著降低了徐州26籽粒SSS活性，说明高温抑制2种类型小麦籽粒淀粉合成的酶学机制不同。此外，不同昼夜温差处理（8℃和12℃）间比较发现，高温下两品种籽粒淀粉含量没有明显差异，适温下2品种淀粉含量以温差较大的处理含量较高。灌浆中后期，高温下SS活性随温差增大而升高，SSS和GBSS则以温差小的处理较高；适温下3种关键酶活性均以温差大的处理为高。总之，灌浆期温度较温差对小麦籽粒淀粉合成的影响大。

Английский. 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 of 28℃ and 20℃, and two day-night temperature differences of 12℃and 8℃. The results showed that the contents of total starch and amylopectin were markedly reduced, but amylose content was shghtly 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 enhanced in Yangmai 9, and SSS activity decreased in Xuzhou 26 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.