Roles Of Irrigation Regimes And Chemical Applications In Regulating Amino Acid Contents In Superior And Inferior Spikelets Of Rice

Rice is one of the most important food crops in China,and amino acids in rice grain are important nutrition sources for both people and animals.Therefore,amino acid content in rice grains is a key determinant of rice quality.Synergistic improvement in grain yield and amino acid content in rice grains is of great significance for ensuring food security and meeting social needs.Irrigation is one of the important cultivation measures affecting the yield and quality of rice,whereas the role and mechanism of irrigation regimes in regulating the contents of amino acids in superior and inferior spikelets in rice remain unclear.In this study,an indica inbred Yangdao 6(YD6)and a japonica inbred Jinxiangyu 1(JXY1)were grown in field,and two irrigation regimes were conducted including continuously flooded(CF)and alternate wetting and moderate drying irrigation(AWMD,plants were rewatered when soil water potential reached at-10 kPa at 15-20 cm depth).During the filling period,rice grains were sprayed with spermidine(Spd)and amino-ethoxyvinylglycine(AVG,ethylene synthesis inhibitor),respectively,with water spraying as the control.The roles of irrigation regimes and chemical applications in regulating amino acids in superior and inferior spikelets in rice were investigated.The main results are as follows:1.Compared with the CF,the AWMD not only significantly reduced irrigation water,but also significantly increased rice yield and amino acid content/yield(amino acid content in the grain x grain yield).The amino acid content in graisn at the mid stage of filling(21 to 28 days after anthesis)was significantly correlated with and amino acid content/yield in milled rice.2.In comparison with CF,the AWMD improved morphological and physiological characteristics of rice roots,increased,and effectively promote t before anthesis into free amino acids and transport from vegetative organs such as leaves to grains.Consequently,the AWMD enhanced the synthesis of amino acids in inferior spikelets,and thereby significantly increasing the contents and yeld of amino acids in inferior spikelets.3.Compared with the spraying water(control),spraying either Spd or AVG markedably enhanced activities of arginine decarboxylase,S-adenosylmethionine decarboxylase,and polyamine oxidase,increased Spd and spermine contents,reduced ethylene evolution rate and 1-aminocyclopropane-1-carboxylic acid content from or in the superior and inferior spikelets,and increased the contents/yield of amino acids in rice grains under CI and AWMD regimes.These results indicate that grain yield and amino acid content/yield in rice could be synergically increased by adopting an AWMD regime(the threshold of soil water potential for rewatering was-15 kPa at 15-20 cm depth)and/or by applying either poly amines or ethylene biosynthesis inhibitors during the grain filling period.