Effects Of Pre-Anthesis Drought Hardening On Grain Yield And Quality Formation In Wheat Under Post-Anthesis Drought And Its Physiological Mechanism

Drought is one of the major limiting factors influencing wheat (Triticum aestivum L) production. The period between anthesis and maturity is critical for grain yield and quality formation. Then, post-anthesis drought significantly reduced grain yield and influenced quality. This article attempts to discuss effect of pre-anthesis drought hardening on drought tolerance during post-anthesis drought in wheat and its physiological mechanism. To impact on crop yield and quality formation, three experiment were done during 2008～2010.Experiment 1:In this study, wheat plants were subjected to three times of 5-day drought pretreatments at three pre-anthesis stages (five-leaf stage, seven-leaf stage and nine-leaf stage), and then followed a 10-day post-anthesis drought stress from 7 days after post-anthesis (DAA) in a pot culture experiment. Thus, four treatments were established from 7 DAA:(1) DS, pre-anthesis middle drought hardening and post-anthesis serious drought; (2) CS, pre-anthesis non-drought stress and post-anthesis serious drought; (3) DM, pre-anthesis middle drought hardening and post-anthesis middle drought; (4) CM, pre-anthesis non-drought stress and post-anthesis middle drought; (5) DC, pre-anthesis drought hardening and post-anthesis non-drought; (6) CC, non-drought stress during both pre-anthesis and post-anthesis. The performances of flag leaf photosynthesis, chlorophyll fluorescence traits and carbon and nitrogen metabolism were then investigated. And further studies in grain yield and quality physiology of wheat. The main results were as follows:1. Pre-anthesis drought hardening improved flag leaf photosynthetic capacity in wheat under drought during grain filling.Compared with non-prehardening treatment, pre-anthesis drought hardening enhanced effectively photosynthetic capacity in wheat flag leaf under drought during grain filling, by increasing stomatal conductance (Gs) and transpiration rate (Tr) and maintaining higher SPAD value, protecting of photosystemⅡand enhancing its photochemical conversion of absorbed light energy via maitainance of high PSII maximum photochemical efficiency (Fv/Fm), photochemical quenching of chlorophyll fluorescence (qP), actual photosynthetic efficiency (ΦPSII).2. Pre-anthesis drought hardening regulated carbon and nitrogen accumulation and redistribution, advanced grain yield and affected grain and flour quality in wheat under drought during grain fillingCompared with non-pretreatment, pre-anthesis drought hardening improved effectively grain dry matter accumulation in wheat under drought during grain filling, by enhancing dry matter accumulation after anthesis and its contribution to grain mass and increased grain protein content and its accumulation, as a result of enhancing redistribution amountof pre-anthesis accumulated nitrogen (NRA) and its contribution to grain nitrogen. Pre-anthesis drought hardening significantly increased 1000-kernel weight, and consequently improved grain yield of wheat under a sever post-anthesis drought, compared with the non pretreated plants. Pre-anthesis drought hardening increased contents of amylopectin and total starch and amylopectin/amylose, and reduced peak viscosity, hold trough, breakdown, final viscosity, set-back and peak time. Pre-anthesis drought hardening also caused significantly increases in grain total protein, gliadin, GMP contents, and, while decreases in grain albumin, globulin, glutelin, glutelin/gliadin, insoluble, compared with the non pretreated plants.In conclusion, pre-anthesis drought hardening improved photosynthetic and antioxidant capacity in wheat flag leaf and regulated effectively carbon and nitrogen metabolism under drought during grain filling. Finally, pre-anthesis drought hardening improved markedly grain yield, compared with the non pretreated plants, while it affected grain quality.Experiment 2:In a solution culture experiment,15N isotope was used to trace the N source for grain protein. The effects of post-anthesis osmotic stress on wheat grain yield, concentrations of protein and its components, and N source for grain protein and its components were investigated. Post-anthesis osmotic stress caused obvious reductions in wheat flag leaf chlorophyll content, stomatal conductance, transpiration rate and photosynthetic rate, and accelerated leaf senescence. This further resulted in decreases in grain number per ear and thousand grain weight, and the final yield. However, post-anthesis osmotic stress significantly increased the transfer amount of pre-anthesis stored photo-assimilates to grain and its contribution to grain mass, while significantly reduced the redistribution amount of nitrogen stored before anthesis to grain, amount of post-anthesis and pre-anthesis accumulated nitrogen, and the fraction of post-anthesis accumulated nitrogen in total protein, albumin, globulin, gliadin, and the insoluble residue protein. Concentrations of grain protein and its components increased due to post-anthesis osmotic stress. Post-anthesis osmotic stress also decreased the fraction of post-anthesis accumulated nitrogen in the protein components, while increased the fraction of pre-anthesis accumulated nitrogen in the protein components.