Physiological Mechanism Of Yield And Quality Formation Of Waxy Maize At Grain Filling Stage Under Different Drought Stress Degrees

Drought stress is one of the most important abiotic stress factors that affecting maize(Zea mays L.)yield and quality.The seasonal drought frequently occurs during maize growth period in Southern China and seriously hinder the development of maize industry and food security.Grain filling stage is the critical period of yield and quality formation and water shortage in this period inhibits the improvement of yield and quality of maize.The grain yield and quality under different drought stress degrees at grain filling stage(1-30 days after pollination)were studied,and endogenous hormones and enzymatic activities involved in starch and protein biosynthesis were clarified.The experimental cultivars are Jingkenuo2000(JKN2000)and Suyunuo5(SYN5).The soil moisture content in the pot under control,mild,medium,and severe water deficit stresses are about 75%,65%,55%,and 45%,respectively.The results can provide a theoretical basis for waxy maize stress resistance and stable yield and high-quality cultivation in arid environment.The main results are as follows:1.Grain yield and its compositionThe grain numbers and weight were significantly decreased by drought stress during grain filling and ultimately induced grain yield loss.The loss of grain yield was gradually aggravated with the intensify of drought stress degrees,and the yield loss(mean of two years)under mild,medium and severe drought stresses were 15%,43%and 64%for JKN2000,and were 15%,33%and 53%for SYN5,and the drought resistance in JKN2000 was higher in SYN5.2.Grain compositionThe contents of soluble sugar and starch in grains were significantly decreased,whereas the content of crude protein and glutenin were significantly increased under drought stress at grain filling stage,and the changes were more turbulent with the aggravation of drought stress.Under mild,medium and severe drought stresses,the decrease of starch and soluble sugar contents in SYN5 was less than that in JKN2000,whereas the increase of protein content in SYN5 was higher than that in JKN2000.3.Endogenous hormone contents and enzymatic activities involved in grain developmentDuring 15-30 days after pollination,the contents of BR,ZR,Z,IAA,CTK and GA3 in grains were significantly decreased by drought and the decrease was aggravated with the intensification of water deficit.However,drought stress significantly increased the content of ABA in grains,and the increase gradually intensified with the deepening of water deficit degrees.During 15-30 days after pollination,the enzymatic activities involved in nitrogen metabolism(NR,GS and GOGAT)were significantly increased under different drought stresses,whereas the activities of sucrose synthetic enzymes(SPS and SS)and starch synthetic enzymes(SSS,SBE,AGP,α-SH and β-SH)were significantly decreased under different drought stresses,and the effects were the most serious under severe drought stress.The results of correlation analysis indicated that the lower contents of BR,IAA,CTK and GA3,downregulated activities of SSS and SBE,and increased activities of GS and GOGAT were the important reasons of lower starch content,grain weight and yield.4.Physicochemical properties of waxy maize flour and starchFor the flour,the gelatinization enthalpy and temperatures(onset,peak and conclusion temperatures)and retrogradation enthalpy were significantly affected by severe drought stress.The retrogradation percentage of JKN2000 was significantly decreased by drought stresses,whereas that of SYN5 was significantly increased under mild and medium drought stresses.Drought stresses significantly reduced the peak and trough viscosities,and the reduction were most serious under severe drought stress.Meanwhile,the peak viscosity of SYN5 was higher than that of JKN2000.Correlation analysis showed that the retrogradation percentage was positively correlated with starch content,the peak and trough viscosities were positively correlated with starch and soluble sugar content,the peak viscosity was negatively correlated with protein content,and the final viscosity was significantly positively correlated with starch content.Those correlations indicated that the increased protein content and decreased starch content are the main reason of the deterioration of pasting viscosities.For the starch,drought stress increased the average granule size,maximum absorption wavelength and relative crystallinity.The peak viscosity decreased significantly under medium and severe drought stresses,and the decrease was the most serious under severe drought.The starch gelatinization enthalpy was decreased under drought stress,and the decrease was most serious under severe drought stress.The starch retrogradation percentage in response to drought was significantly different between the two cultivars,it was significantly increased under drought stress SYN5,JKN2000 had opposite changes at the two years,which was significantly increased under drought stress in 2019,and significantly decreased under drought stress in 2020.Correlation analysis showed that the peak,trough and final viscosities were negatively correlated with average granule size,and the pasting temperature was positively correlated with relative crystallinity.The gelatinization enthalpy was negatively correlated with iodine binding capacity,maximum absorption wavelength,relative crystallinity and average granule size,the onset and peak temperatures were negatively correlated with relative crystallinity and average granule size,and the retrogradation percentage was positively correlated with maximum absorption wavelength and average granule size.