Effects of Irrigation Amount on Grain Starch Content,Starch Synthase Activity,and Water Use Efficiency in Wheat

Water deficiency is one of the main factors limiting wheat(Triticum aestivum L.) production.Grain starch,which comprises 65–70% of the dry weight in grains,is influenced by some eco-environmental factors,such as temperature and water content in soil.To study the effects of irrigation stage and amount on grain yield and water use efficiency(WUE),field experiments were carried out in Tai’an and Yanzhou,Shandong Province in 2004–2006 growing seasons with a high-yielding wheat cultivar Jimai 20.The water contents of soil layers within 0–140 cm(2004–2005) or 0–200 cm(2005–2006) were monitored under different irrigation regimes.The treatments of irrigation were at jointing and anthesis stages(W1),and at jointing,anthesis and grain filling stages(W2) with 60 mm water each time in 2004–2005 growing season as well as at jointing and anthesis stages in 2005–2006 growing season with 30 mm(deficient irrigation),60 mm(moderate irrigation),or 90 mm(luxury irrigation) water per irrigation.No irrigation was taken as the control.The grain starch content and the relative enzyme activity were measured at every 7 d interval after anthesis.The soluble starch synthase(SSS) activity and granule bound starch synthase(GBSS) activity significantly increased at early filling stage and reduced from middle to late filling stage,and the contents of amylopectin,amylose,and starch significantly reduced at late filling stage in the control.Moderate irrigation at jointing and anthesis with 60 mm water each time was in favor of keeping high activities of SSS and GBSS from middle to late grain filling stages.The moderate irrigation had higher levels on the contents of amylopectin,amylose,and starch at late filling stage than the control.However over irrigation significantly reduced the SSS activity and significantly increased the GBSS activity at middle and late filling stages,while over irrigation significantly reduced the amylopectin content and significantly increased the amylose content at late filling stage.Moderate irrigation at jointing and anthesis with 60 mm water each time obtained the highest WUE in the both growing seasons.Over irrigation significantly increased the soil moisture content in 0–60 cm soil layers,significantly reduced the soil water consumption amount,WUE and irrigation water use efficiency,and not significantly increased grain yield.