Effects of transient high temperature during grain filling period on starch formation in wheat (Triticum aestivum L.)

Китайский. 采用人工气候室控温，研究了灌浆期高温对弱、中筋2个小麦品种淀粉形成的影响。结果表明，温度从25℃升至30℃有利于籽粒总淀粉积累，当灌浆温度超过30℃时，温度升高，总淀粉含量下降，40℃时总淀粉含量最低。在相同温度条件下，小麦淀粉的形成以花后第25―27天高温胁迫影响最大，花后第33―35天高温胁迫影响最小。当温度超过25℃时，随温度的升高，剑叶可溶性糖、蔗糖含量和SPS酶活性呈下降趋势。40℃处理使SS、SBE酶活性最低，峰值在25―30℃之间。40℃高温胁迫下，弱筋小麦扬麦9号籽粒淀粉粒呈椭圆型，与蛋白质鞘结合较疏松，角质化程度低；中筋小麦扬麦12籽粒淀粉粒受到伤害，呈扁圆形，并出现裂纹，说明灌浆期短暂高温胁迫对扬麦12的影响大于对扬麦9号。

Английский. Wheat grain quality is affected by the environment. Temperature is a major component in environmental variation and has a marked effect on grain filling in wheat. Short period of heat shock, such as over 30 ℃ for a few days, happens frequently during grain filling in China and many wheat-growing areas in the world, and has become an important factor limiting wheat quality. Starch is the major storage substance in grains of wheat, comprising 65%-70% of dry weight. Investigating the effects of transient high temperature during grain filling period on starch formation and its context is useful for understanding the mechanism of heat damage and improving wheat quality under high temperature stress. Four temperature levels, i.e. daily average temperature 25℃, 30℃, 35℃ and 40℃, respectively, were set in a phytotron. Wheat plants during different grain filling stages, including the 15th-17th, 19th-21st, 25th-27th and 33rd-35th day after anthesis （DAA）, were treated. The tested wheat cuhivars were Yangmai 9 with weak-gluten and Yangmai 12 with medium-gluten. Results showed that grain starch content was highest in the treatment of 30℃ and was lowest in the treatment of 40℃ in two cuhivars . Under the same temperature, the effects of heat shock during the 25th-27th DAA were greatest, while that during the 33rd-35th DAA were the lowest （Table 1）. For the treatments of the 25th-27th DAA, the higher the temperature, the lower the soluble sugar and sucrose contents and sucrose phosphate synthase （SPS） activity in flag leaves. Sucrose synthase （SS）, starch branching enzyme （SBE） activities were the lowest in 40℃ treatment, and SS and SBE activities reached maximum in 25-30℃ treatments （Fig. 2-4）. As for starch morphology, the granules in grains were in ellipsoid shape and combined loosely with protein sheath for 40℃ treatment of Yangmai 9 （ Plate Ⅰ-3, 4）, but were damaged and in flat ball shape with a crack for that of Yangmai 12 （Plate Ⅰ -7, 8）. Starch granules of Yangmai 9 were slightly damaged for 30℃ treatment （Plate Ⅰ -1, 2）. At the 1st day after 30℃ heat shock treatment, the cracked granules were observed for Yangmai 12, but disappeared at maturity （Plate Ⅰ -5, 6）. While in 40℃ treatment, the crack could still be observed at maturity. It indicated that the heat damage at 30℃ for 3d could be considerably compensated other than at 40℃. It was probable that a kind of protective mechanism for enzymes existed in the endosperm, which had the critical temperature of 30℃. Resistance to high temperature varied with cultivars, and Yangmai 9 was stronger than Yangmai 12.