Physiological Response To Drought Stress For Non-structural Carbohydrates Accumulation And Remobilization In Winter Wheat At Grain-filling Stage

Wheat yield formation associated with the production of photosynthetic products, and also dependedon highly efficient remobilization and redistribution of non-structural carbohydrates (WSC) to grain duringthe filling stage. In particular, under the drought stress, promoting the remobilization of WSC in vegetativeorgans to wheat grain could improve grain filling and increase grain weight. It could compensate the lossof grain yield and enhance the water use efficiency. Deeply exploring the physiological mechanism onWSC accumulation and remobilization to improve grain filling regulated the drought stress would be ofvery importance in the drought-resistant genetic improvement and efficient cultivation of wheat. Therefore,two winter wheat cultivars, Longjian19(Drought-resistant) and Q9086(Drought-sensitive), were selectedas materials under different water conditions to explore the physiological mechanism on WSCaccumulation and remobilization of different vegetative organs responded to drought stress in wheat duringgrain filling period. The results are as follows:1. Net-photosynthetic rate (Pn), chlorophyll content (ChlC), Fm and Fv/Fm were gradually reducedwith the grain filling process under different water treatments, but the trend opposite to Fo. Phenotypicvalues of all target traits, except Fo, in well-watered condition were significantly higher than those indrought stress. Under drought stress, Longjian19(Drought-resistant) changed smaller in phenotypic andremained higher in ChlC and Pn, while Q9086was opposite. Drought stress significantly improved thegrain filling rate (GFR) of Q9086in the early stage of filling, advanced its peak, and shortened the fillingcycle. Longjian19kept higher GFR in whole grain-filling period. Meanwhile, drought stress causedthousand grain weight (TGW) of Longjian19and Q9086significant decline of9.27%and22.25%,respectively. Under drought stress, TGW was negatively correlated with Pn, ChlC, Fm and Fv/Fm,respectively, while positively correlated with Fo. It was opposite to the well-watered condition. Thecorrelation coefficients under well watered were higher than that under drought stress.2. Under the drought stress, total stem soluble carbohydrates (WSC) and sucrose content were higherthan well watered, and Longjian19higher than Q9086. Sucrose content of the flag leaf was jointlycontrolled by Sucrose-phosphate synhase (SPS) and sucrose synthase (SS) activities. Drought stressincreased sucrose supply capacity in flag leaf of wheat during the early stage of grain filling, but decreasedsupply capacity during lately stage of grain filling, and improve of GFR in the early stage of grain filling ofQ9086and in full-filling stage of Longjian19. TGW had no significant correlations with WSC content andsucrose content of flag leaf and peduncle internode, but had significant negative correlation withpenultimate internode, other internodes. Sucrose content of the flag leaf was positively correlated withGFR, but correlation with the WSC content was not significant. Filling stage WSC total output showLongjian19(Drought stress)> Longjian19(Well watered)> Q9086(Drought stress)> Q9086(Wellwatered).3. The sink-cutting treatment significantly increased WSC contents of different vegetative organs andpositively promoted the WSC relative transporting, while the source-cutting caused opposite response. Thesource-sink regulation showed stronger impact on WSC contents, its relative transporting amount (RTA) and relative transporting percentage (RTP) under the following factors, such as the DS condition, thedrought-resistant cultivar (Longjian19), the sink-cutting, and organs (peduncle internodes, PedI andPenultimate internodes, PenI) than the corresponding factors, the WW condition, the drought-sensitivecultivar (Q9086), the source-cutting and other organs (leaves, sheath and other internodes, OthI). Under thesource-cutting, the superior organs of Longjian19on RTP of total WSC concentrated on sheath, PedI andPenI which also contributed to the fructan RTP with two cultivars, while the corresponding superior organsof Q9086were PenI and OthI. The source-cutting significantly decreased TGM of Longjian19and Q9086,up to27.25%and31.68%under the DS，while25.31%and12.14%under the WW. The correlationcoefficient between TGM and WSC contents, RTA and RTP significantly higher when treated with thesink-cutting than that treated with the source-cutting; also higher under the DS condition than that under theWW condition. Moreover, there existed higher correlation coefficient (r2>0.900) between TGM, totalWSC and fructan contents in different vegetative organs. The tight relational grade between TGM andWSC contents, its RTA and RTP mainly focused on sheath and PedI. Under the DS condition, the traitsassociated with total WSC contents showed higher relational grade with TGM. However, Under the WWcondition, the traits associated with sucrose and glucan contents generally showed higher relational gradewith TGM. It indicated that effects of source-sink regulation on WSC of vegetative organs and TGM weresensitive to the variation of soil water environments, wheat genotypes, as well as vegetative organlocations.4. Sucrose synthase (SS), ADPG-gluose pyrophosphorylase (AGPase), soluble starch synthase (SSS)and Granule-Bound starch synthase (GBSS) activity showed a single peak curve change, and SS, AGPaseand SSS activity after anthesis28d reached the peak values during Grain Filling stage of Longjian19andQ9086. SS and AGPase activity of Longjian19performance drought stress> Well watered in front of thepeak, and no significantly different was found after the peak. SSS activity of Q9086show Drought stress>Well watered in the whole growth period. SS and AGPase activity was not significantly different in twowater conditions. The peak value of GBSS activity delayed by7d, show Drought stress> Well watered. Inshort, drought stress significantly improved SS, AGPase, and SSS activity of Longjian19in the early stageof grain filling, and the increased range associated with genotype, Longjian19> Q9086. SS, AGPaseactivity and GFR was significantly negatively correlated. SSS, GBSS activity was not a significant positivecorrelation; Under different water conditions, correlation coefficient of grain starch enzyme and grainfilling rate show Well watered> Drought stress. Under drought stress, TGW and SS, AGPase, SSS,GBSS activity was negatively correlated, and the correlation coefficient show Well watered> Droughtstress. Under Well watered, those was positively correlated, and the correlation coefficient show Droughtstress> Well watered.