Abstract: 【Objective】 The purpose of this study was to test the effects of high temperature stress and spraying exogenous absisic acid (ABA) post-anthesis on endosperm cell division, grain filling and changes of endogenous hormones in different types of stay-green wheat cultivars, and provide a theoretical basis for enhancing grain weight and minimizing the loss of grain yield result from high temperature. 【Method】 Both Wennong 6 (a stay-green cultivar) and Jimai 20(a non-stay-green cultivar) were grown in the experimental plots covered with transparent plastic sheds at 1 to 5 days after anthesis (DAA), which were mimicked the high temperature that occurs during the natural heat event in this region, whilst exogenous ABA (10 mg?L-1) to the spikes was sprayed at the rate of 100 mL?m-2 between 5 pm and 6 pm from 1 to 3 DAA. High performance liquid chromatography method (HPLC) and a simple method of endosperm cell number determination were used to determine endogenous hormones contents and endosperm cell number, respectively. Both grain filling process and endosperm cell division process were simulated by Richard equation, and then the related parameters were calculated. 【Result】 The endosperm cell number of superior and inferior grains in both cultivars were significantly decreased by high temperature stress, and the endosperm cell division rate was markedly decreased. However, high temperature extended the active endosperm cell division period and the division duration. The grain filling rate of inferior grains in both cultivars was decreased in the high temperature treatment. Grain-filling duration and the active growth phase were also reduced in the high temperature treatment. High temperature after anthesis significantly decreased the number of grains per spike and thousand-grain weight. In contrast, Wennong 6 showed 3.7 and 8.2 grain/spike reduction in superior and inferior grains, respectively. Similarly, Jimai 20 was reduced by 1.3 and 4.3 grain/spike in superior and inferior grains, respectively. The final grain yield of Jimai 20 decreased by 26.22% due to high temperature treatment, and that of Wennong6 decreased only by 19.65%. Spraying exogenous ABA obviously improved grain filling rate, endosperm division rate and increased endosperm cell number in both normal and high temperature treatments. Although the zeatin riboside (ZR) contents in superior and inferior grains were significantly decreased in the high temperature treatment, the gibberellin (GA3) contents in Jimai 20 were markedly enhanced at 3 to 27 DAA, and those in Wennong 6 were also increased at 12 to 27 DAA. The auxin (IAA) content of inferior grains in Wennong 6 was significantly decreased at 15 to 27 DAA in high temperature treatment. The ZR content of superior grains in Jimai 20 was decreased at 3 to 9 DAA by spraying exogenous ABA in the high temperature treatment, but endogenous ABA content of superior grains in Jimai 20 was obviously increased at 3 to 28 DAA and that in Wennong 6 was also increased at 3 to 18 DAA. In the normal temperature treatment, spraying ABA significantly decreased the GA3 contents in both Wennong 6 and Jimai 20. Together, spraying exogenous ABA decreased the GA3 contents of superior and inferior grains in Wennng 6 at 3 to 27 DAA in high temperature treatment, and decreased those in Jimai 20 at 3 to12 DAA and 6 to 15 DAA, respectively. In the normal temperature treatment spraying ABA increased IAA content of superior grains in Jimai 20 at 12 to 18 DAA, and also increased that in Wennong 6 at 6 to 18 DAA. Meanwhile, IAA contents of inferior grains in both cultivars were significantly improved at 6 to 27 DAA. In addition, compared with Jimai 20, Wennong 6 had longer grain-filling duration and the active growth phase, higher mean grain-filling rate and maximum grain-filling rate, larger thousand-grain weight, and greater grain yield.【Conclusion】Both no-stay-green cultivar and inferior grains of the two cultivars were much more influenced by high temperature stress. Grain weight and yield reduction result from high temperature decreased kernel sink and grain filling rate. Exogenous ABA improved grain yield due to increasing the grain sink capacity and grain filling rate through regulating endogenous hormones contents to promote endosperm division and photosynthate accumulation in normal treatment and high temperature stress.

Key words: high temperature , endogenous hormones , stay-green , endosperm cell number , grain filling