Effect of Temperature at Grain Filling Stage on Activities of Key Enzymes Related to Starch Synthesis and Grain Quality of Rice

Three japonica rice varieties with different cooking and eating quality were grown at high temperature in the greenhouse and natural field. Effects of temperature at the grain filling stage on these varieties were investigated in terms of the activities of key enzymes related to starch synthesis and cooking and eating quality of rice grain. The high temperature at the grain filling stage increased protein content, and decreased amylose content and taste meter value of rice; inferior grain quality varieties showed a greater magnitude of the increase or decrease than the superior ones. Reaction of rapid visco analyser profiles to the temperature varied with rice varieties. The activities of adenosine diphosphoglucose pyrophosphoryiase （AGPP）, soluble starch synthase （SSS） and starch branching enzyme （SBE） gradually increased to a peak value, and thereafter declined as grain filling progressed. Enzyme activities in different varieties differed in a same filling stage, and also in the time when the enzyme activity reached a maximum. AGPP and SSS were insensitive to the environmental temperature, but SBE was comparatively sensitive to the temperature, and its activity declined when temperature was too high or too low.

Effect of Different Irrigation Patterns on Transportation and Allocation of Carbohydrate During Grain Filling of Rice

Using intersubspecific hybrid rice Xieyou 9308 and Liangyou Peijiu as the tested materials, the effects of differentirrigation patterns on transportation and allocation of carbohydrate during grain filling stage was observed by the designwith three level of soil water content in irrigated field. The results showed that in the conventional flooding and thealternate dry-watering cultivations, the exported rate of stored carbohydrate from stem and photophate from the leaves were60 and 90 % respectively. The exported rate of carbohydrate was decreased significantly (P<0.01) in the non-floodingcultivation. There was no significant difference between the conventional flooding and dry-wet alternation treatments interm of the exported rate of carbohydrate. The filling grains were the major sinks for carbohydrate storage during grainfilling stage. Grains received nearly 50% of stored carbohydrate from leaf sheath and 80% of photophate from leaves. Atthe nonflooding condition the absorbing rates of grains were significantly decreased by 10 % from leaf sheath and 20 %from leaves photophate. Water stress leaded much decrease in absorbing ability for inferior grains, which might be one ofthe main causes for low seed-settling rate in non-flooding cultivation.

Effect of Drought Stress on Proteome of Maize Grain during Grain Filling

Based on isobaric tags for relative and absolute quantification(iTRAQ)technology,the proteome of grains of a maize cultivar Huangzao 4 under drought stress at grain filling stage was analyzed.The results show that under drought stress,438 proteins were differentially expressed in the maize grains during grain filling.Among them,200 were up-regulated and 238 were down-regulated.The gene ontology(GO)analysis shows that the biological processes in which differential proteins are more involved are cellular processes,metabolic processes and single biological processes;proteins in the cell component category are mainly distributed in cells,cell parts and organelles;and the proteins the molecular function category mainly possess catalytic activity and binding function.Differentially expressed proteins classified by COG are mainly involved in protein post-translational modification and transport,molecular chaperones,general functional genes,translation,ribosomal structure,biosynthesis,energy production and transformation,carbohydrate transport and metabolism,amino acid transport and metabolism,etc.The subcellular structure of the differentially expressed proteins is mainly located in the cell chloroplast and cytosol.The proportions are 35.01%and 30.21%respectively.KEGG metabolic pathway enrichment analysis shows that the differentially expressed proteins are mostly involved in antibiotic biosynthesis,microbial metabolism in different environments,and endoplasmic reticulum protein processing;the metabolic pathways with higher enrichment are the carbon fixation pathway and estrogen signaling pathway of prokaryotes;and the higher enrichment and greater significance are in the tricarboxylic acid cycle,carbon fixation of photosynthetic organisms and proteasome.The results of this study preliminarily reveal the adaptive mechanism of maize grains in response to drought stress during grain filling,providing a theoretical reference for maize drought-resistant molecular breeding.