Abstract: Temperature and water are the main climatic factors affecting grain quality in wheat (Triticum aestivum). The growth-chamber experiments were carried out to investigate the effects of high temperature and water stress conditions during grain filling on the activities of key regulatory enzymes for protein accumulation and contents of protein components in wheat grains. Two wheat cultivars Yangmai 9 with low protein content and Yumai 34 with high protein content were grown under two day/night temperature regimes of 32℃/24℃ and 24℃/16℃, respectively. For each temperature regime, three soil water levels were established as moderate water status (soil relative water content, SRWC=75%–80%), drought (SRWC=45%–50%), and waterlogging. The results showed that protein and protein component contents in grains were affected significantly by high temperature, water, and temperature×water. High temperature enhanced protein content, but reduced glutenin /gliadin ratio. Under both optimum temperature and high temperature, drought enhanced protein content. Drought enhanced glutenin /gliadin ratio under optimum temperature, but reduced it under high temperature. Under both high and optimum temperatures, waterlogging reduced protein content and glutenin /gliadin ratio. Protein content was the highest at high temperature × drought, and the lowest at optimum temperature × waterlogging. Under high temperature and water stresses, differences in protein content and glutenin /gliadin ratio were caused mainly by changes in gliadin and glutenin contents. Both high temperature and water stress reduced glutamine synthase (GS) activity in flag leaves and glutamate pyruvic amino transferase （GPT） activity in grains, and both enzymes in the treatments were CK>drought>waterlogging. The responses of GS and GPT activities to high temperature and water stress differed between two cultivars with different grain protein contents. Under optimum temperature, GS activity in flag leaves was more affected by water stress for Yumai 34 and was more inhibited by high temperature for Yangmai 9. Opposite trend was found under high temperature.

Key words: Wheat, High temperature, Water stress, Protein accumulation, Enzyme activity