| Temperature and water are main ecological factors affecting formation of wheat quality. Elucidating the physiological mechanism for the effects of high temperature and water stress on grain quality formation in wheat is of great importance for understanding grain quality physiology and guiding cultural management in wheat. Two wheat cultivars differing in protein content including Yangrnai 9 and Xuzhou 26 were grown under varied temperature conditions during grain filling including 32~C/24~C, 28~C/20~C and 24~C/16 ~C in one experiment and 34~C/22~C, 32~C/24~C, 26~C/14~C and 24~C/16~C in the other experiment. Two wheat cultivars including Yangmai 9 with low protein content and Yumai 34 with high protein content were subject to temperature and water stress conditions in the third experiment. Two day/night temperature regimes of 32~C/24~C and 24~C/16~C with three soil water regimes were established as moderate water status (soil relative water content, SRWC=75%-80%), drought (SRWC=45%-50%) and waterlogging. The quality formation, photosynthetic characters, C/N assimilates translocation and regulatory enzyme activities in relation to formation of grain quality were investigated comprehensively, and the physiological regulatory mechanisms of high temperature and water stress on wheat quality formation was elucidated. The main results were as follows:Contents of crude protein, albumin, globulin and gliadin in grains were significantly enhanced, but glutenin content was reduced by high temperatures, which resulted in decrease of the ratio of glutenin to gliadin. Moreover, contents of total starch, amylose and amylopectin were reduced, but more seriously effect of high temperature on amylopectin than amylose resulted in reducing amylopectin/amylose ratio. In addition, optimum diurnal temperature difference favoring the formations of grain protein and starch differed in wheat genotypes, but the effects of temperature level on protein and starch content were much higher than temperature differences. The second experiment showed that the effect of high temperature on grain protein and starch content were more marked than that of water stress, and the interaction effect of temperature X water also existed. Under high temperature or optimum temperature, grain protein content exhibited the pattern of drought>CK>waterlogging, the highest under drought with high temperature and the lowest under waterlogging with optimum temperature. Grain starch content showed the order CK>drought> waterlogging, the highest under CK with optimum temperature and the lowest under waterlogging with high temperature Furthermore, the content of grain gliadin was enhanced under high temperature and water stresses, while the contents of glutenin and amylopectin were reduced, which resulted in decreased tha ratios of glutenin to gliadin and amylopectin to amylose. Especially, the effect of high temperature with waterlogging was the most significant on protein and starch components. In addition, the response of Yumai 34 in grain protein formation to high temperature and water stresses were more serious than in starch, but for Yangrnai 9, starch formation was more sensitive to high temperature and water stresses. Correlation analysis revealed that protein content was positively correlated to albumin and gliadin contents, but slightly negatively to glutenin content. Starch content was positively to the contents of glutenin and amylopectin and amylopectin/amylose ratio under high temperature and water stresses. High temperature and water stress had different effects on grain gluten characters and sedimentation value in different varieties.High temperature enhanced free amino acid content in vegetative organs, but significantly reduced soluble sugar content in vegetative organs and kernels during whole grain filling so that ratio of sugar/amino decreased. High temperature reduced remobilization amount and rate of pre-anthesis assimilates and nitrogen stored in vegetative organs and transferring into grain. Effect of diurnal temperature difference on amino acid content differed between cultivars. Under high temperature, temperature difference affected soluble sugar content slightly. Uunder optimum temperature, soluble sugar content under greater diurnal temperature difference was higher than that under lower temperature difference. Under high temperature, day/night temperature difference affected ratio of C/N slightly. Under optimum temperature ratio of C/N was higher under the day/night temperature difference of 12~C. Drought enhanced free amino acid content in vegetative organs, but reduced soluble sugar content in vegetative organs and kernels. As a result, ratio of C/N decreased under high temperature and drought. Under high and optimum temperature, waterlogging reduced contents of amino acid and soluble sugar vegetative organs and kernels. Effect of waterlogging on ratio of C/N differed among different cultivars and organs in wheat. Amount and ratio of assimilates and nitrogen translocation declined as drought>control>waterlogging under optimum temperature, while declined as control>drought>waterlogging under high temperature. The amounts of post-anthesis assimilate transferring into grain were declined as CK>waterlogging>drought under optimum temperature,while the order was CK>drought>waterlogging under high temperature.The amounts of post-anthesis accumulated nitrogen declined as CK>waterlogging>drought under both high and optimum temperature.The amounts of pre-anthesis stored and post-anthesis accumulated nitrogen transferring into grain were significantly related to protein yield.The amounts of pre-anthesis stored and post-anthesis accumulated assimilates transferring into grain were significantly related to grain weight and starch content.Under optimum water status,high temperature enhanced the activities of sucrose synthase (SS) and granule-bound starch synthase (GBSS) at early stage of grain filling, while reduced activities of SS,GBSS and soluble starch synthase (SSS) at late grain filling stage.Activities of three enzymes were reduced by high temperature in Yumai 34.High temperature significantly reduced activity of SSS in Xuzhou 26 at early stage of grain filling.Those results indicated that the enzymatic mechanism of starch formation differed among wheat varieties.In addition,under high temperatures,SS activity was higher at 34℃/22℃during the middle and late stage of grain filling,whereas the activities of SSS and GBSS were higher under 32℃/24℃.Under optimum temperature,activities of three enzymes were higher at bigger day/night temperature difference.At different day-night temperature differences, GPT (glutamate pyruvic aminotransferase) and glutamine synthase (GS) activities changed between cultivars.Effects of drought and waterlogging on activities of three enzymes differed between different cultivars.Drought and waterlogging reduced activities of three enzymes under both high and optimum temperature.Compared with optimum temperature,high temperature reduced GPT activity in kernels for two wheat cultivars.But reduced GS activity in flag leaves of Yangmai 9 and enhanced GS activity of Xuzhou 26 on 14 DAA.At different day-night temperature differences,GPT and GS activities changed between cultivars.High temperature,drought and waterlogging reduced GS activity and GPT activities in flag leaves.The effects of drought and waterlogging on activities of enzymes involved in protein formation were different among different cultivars and temperatures.Results of correlation analyses indicated that the SPS,SSS and GBSS activities were closely correlated to the yield of starch. GS activity in grains was correlated to a lower degree to the yield and content of protein than GS in flag leaves and GPT ingrains.Under high temperature,the effects of high temperature and water stresses on grain quality and protein and starch accumulation aggravated.High temperature,drought and watedogging reduced photosynthetic rate and chlorophyll content in flag leaves,and the consequences of drought and waterlogging were more severe under high temperature than under optimum temperature.High temperature, drought and waterlogging enhanced the content of malondiadehyde (MDA),while reduced soluble protein content in flag leaves.Under optimum water treatment,compared with optimal temperature treatment,during the early stage of high temperature treatment,activity of SOD was enhanced but dropped rapidly during late grain filling.Under optimum and high temperature, drought and waterlogging reduced SOD activity on both 15DAA and 20DAA.These results indicated that the membrane lipid peroxidation was accelerated and the permeability of plasma membrane increased as the high temperature treatment prolonged and accelerated leaf senescence.The effects of drought and waterlogging on flag leave were not reversed.The consequences of drought and waterlogging were more severe under high temperature than under optimum temperature.Higher temperature difference under high temperature condition increased senescence of flag leaf,while under optimal temperature condition,higher temperature difference delayed the plant senescence.In summary,high temperature and water stress reduced the photosynthesis rate in flag leaves of wheat.The amount of post-anthesis assimilates transferred into grains decreased distinctly under high temperature and water stress.High temperature and waterlogging significantly reduced the pre-anthesis stored nitrogen and the translocation of post-anthesis accumulated nitrogen into grains.Thus,the differential substrates caused the differences in protein and starch contents of wheat grains under different water and temperature conditions.The further studies indicated that the activities of key enzymes for grain starch and protein formation,including SPS and GS in leaf,SSS,GBSS and GPT in grains,are the vital enzymatic reasons for affecting the yields and contents of grain starch and protein by high temperature and water stress.The differences between grain qualities under different treatment conditions were caused by the interaction of high temperature and water stress on C/N translocation and activities of key enzymes involved in starch and protein accumulation in wheat... |
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