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With the trends of global warming, the extreme high temperature stress often happens during crop grain filling in the world. Heat stress has been an important factor limiting grain yield and quality. To determine the effects of heat stress on fresh kernel yield, quality and enzyme activities of sucrose metabolism, we carried out an experiment in artificial phytotron using two sweet corn cultivars (Xiatian 1 and Yuetian 16) with two typical temperature treatments (high temperature, HT and control, CK) during grain filling. The results indicated that the growth process of sweet corn was accelerated, but the weight and quality of kernel was decreased seriously under high temperature. The weight of 100-fresh-kernel and kernel water content were markedly reduced, but content of pericarp was increased. At the optimum harvest stage of fresh ear (with kernel water content 68%-74%), the fresh kernel weight of the two cultivars was reduced significantly by 20.8% (Xiatian 1) and 16.4% (Yuetian 16) under higher temperature respectively. The contents of soluble sugar and sucrose first increased and then decreased during the grain filling stage. High temperature was not favorable to sugar accumulation, resulting in sucrose content decrease and starch content increase. Sucrose phosphate synthetase (SPS) and sucrose synthetase (SS) play an important role in sucrose synthesis and degradation. SS catalyzes the interconversion of sucrose. Heat stress decreased the activities of SPS and SS (synthetic) and increased the activity of SS (cleavage), which inevitably leads to a depression in sucrose content and a reduction in kernel quality. The maximum SS (synthetic) activity in process of grain filling of two sweet corns appeared earlier under high temperature, while that of SPS activity appeared earlier in Xiatian 1 and did not in Yuetian 16.

High temperature after pollination changes the dynamics of grain filling of waxy maize, which may underlie the observed changes in its pasting and thermal properties.

Grain physicochemical properties determine the table quality of fresh waxy maize. Two waxy maize varieties, Suyunuo5 (shading tolerant) and FHN003 (shading sensitive), were used to estimate the effect of shading (plants received 30% less radiation than control) during grain filling (from 0 d to 23 d after pollination) on physicochemical properties of fresh waxy maize grain. Shading decreased the grain fresh weight of Suyunuo5 and FHN003 by 8.4 and 19.1%, respectively. Shading increased the grain water content of FHN003, whereas that of Suyunuo5 was not affected. In both varieties for shading treatment, soluble sugar, starch, and protein content was decreased, whereas zein content was increased. The changes in globulin, albumin, and glutenin content under shading were variety dependent. In both varieties, shading decreased λmax, iodine binding capacity, and the percentage of large starch granules (diameter >17 μm) but increased crystallinity. The results of rapid visco analysis showed that the viscosity characteristics (except for pasting temperature) of both varieties were decreased by shading; however, FHN003 was more severely affected than Suyunuo5. Under shading, Hret and %R was decreased in both varieties, whereas the changes in Hgel and transition temperatures were variety dependent. Hardness, cohesiveness, and chewiness were decreased in both varieties. Significant differences in physicochemical characteristics were observed between the two varieties.