Polyamines And Ethylene Biosynthesis In Response To Water Deficit In Wheat And Its Relations To Grain Filling

The stage of grain filling plays an important role in the grain formation. During grain filling,the sugars and proteins produced by leaves or stems of wheat are stored in the seed by theassimilaton function. Water deficit during grain filling had a negative effect on grain fillingand wheat production, and it indicated that the response mechanism of grain filling to waterdeficit and regulation pathway play important roles in improving grain weight. It proved thatethylene and polyamines play key roles in the responses of crops growth to abiotic stress.However, the relationship of polyamines and ethylene biosynthesis to grain filling and flagleaves photosynthetic characteristics as well as the regulatory mechanism of exogenouschemicals were unclear. The relationships of the ultrastructure of the abdominal phloemtissues characters, the ATPase activity on abdominal phloem tissues and the TaSUT1geneexpression to photoassimilate storage of grains under water deficit need to be furtherinvestigation. It can rich the theory of wheat cultivation under water deficit conditions, andsupply theoretical basis and technical support for the application of exogenous substances.The main results were as follows.1Grain weight of different variety and grain-bit in response to water deficitThe responses of grain weight to water deficit differed with the varieties and grain types.SD reduced the weight of superior and inferior grains, by6.2and23.54%in JM22,13.8and2.2%in SN16, respectively. SD reduced the total grain weight of SN16and JM22by7.6and16.2%respectively. The analysis by using the Richards model indicated that SD reduced the active grain filling stage of superior and inferior grains, by10%and6.1%in JM22,6.7%and6.7%in SN16, respectively. It also suggested that SD educed the average grain-filling rate ofsuperior and inferior grains, by15.8%and9.9%in JM22,0.5%and12.3%in SN16,respectively. Application of exogenous Spd or AVG significantly increased the grain weightunder water deficit, while MGBG or ethephon showed the opposite effects. Changes ofTaSUT1expression levels and sucrose content with the grain filing showed that sucrosetransport capacity may be a major factor limiting grain filling at initial and later grain fillingstage, while the key enzymes involved in the sucrose-to-starch conversation becomes a majorfactor limiting grain filling at middle filling stage.2The responses of polyamines and ethylene biosynthesis to water deficit in wheat and itsrelations to grain fillingHigher Spd and Spm concentration and Put concentration, EER and ACC concentrationwere found in superior grains than those in inferior ones. Opposite to the variations of Spdand Spm concentration, ACC, Put concentration and EER were significantly increased underSD. The percentage variations of PAs and ACC differed with cultivars and grain types. ACCconcentration of superior and inferior grains under SD increased significantly at21DPA, by90%and164%in JM22,65%and13.2%in SN16, respectively. The equivalent value of Putconcentration was1.04%and7.9%in JM22,34.4%and10.3%in SN16. Spd concentrationof superior grains showed a higher decrease than that of inferior ones in both cultivars, whileSpm exhibited an opposite trend between both grain types. These percentage variations werehighly consistent with the differed responses of weight of both grain types to SD in JM22andSN16. SD apparently increased the ACC and Put concentration as well their biosynthesisrelated genes expression, while degraded the Spd biosynthesis. Grain filling rate wasnegatively correlated with EER and ACC concentration, while positively correlated with Spdand Spm concentration as well as the ratio of Spd or Spm to ACC. Exogenous Spd oraminoethoxyvinylglycine obviously reduced ACC concentration and EER and increased Spdand Spm concentration, while exogenous ethephon or methylglyoxal-bis showed the oppositeeffects. SuSase, AGPase and SSSase negatively correlated with ACC and Put concentrations,but positively correlated with Spd concentration and Spd/ACC, indicated that ACC and Spdinteract in mediating the influence of SD on filling. The volume and surface area distribution of starch granules showed a bimodal curve, while the number distribution exhibited aunimodal curve. SD caused a marked drop in grain weight, grain number and starch content,also led to a significant reduction in the proportion (both by volume and by surface area) ofB-type starch granules (<10μm), with an increase in those of A-type starch granules (>10μm). Application of Spd or AVG increased the proportion (both by volume and by surfacearea) of B-type starch granules under SD. Correlation analysis suggested that ethylene andSpd showed an antagonism relation in the formation of B-type granules. These resultssuggested that it would be good for the formation of B-type starch granules to have thephysiological traits of higher Spd and lower ACC concentration and ethylene emission underSD.3Abdominal phloem tissues characters of wheat caryopsis in the responses of grainfilling to water deficitMost of the SEs of the phloem are associated with CCs and have walls contiguous withthose of the PPC. The superior grains under WW at15or20DPA, of which SEs of abdominalphloem were structurally mature, and exhibited a clear lumen and plasma membrane, and CCshad prominent nuclei distributed in dense cytoplasm. At15and20DPA, ICs were found toreside predominantly in SE-CCs complexes. Whereas CCs were hardly observed in inferiorgrains under WW, superior grains under SD and inferior grains under SD. As a consequence,ICs played the functions of long-distance assimilate transport to compensate the decreasedassimilate transport functions of SEs with the development of grain and the extension of waterdeficit. A few CCs was showed in superior grains under WW, while it was hardly observed ininferior ones under WW, superior and inferior grains under SD at25DPA. It is noteworthythat the PPC in inferior grains under SD showed the phenomenon of plasmolysis and nuclearchromatin condensation, and the SEs exhibited the characters of membrane degradation atlater filling stage, suggested that the characters of PPC and SEs in inferior grains was moresensitive to SD than the superior ones. Under WW, ATPase activity on plasma membrane ofSE-CCs complexes and ICs and PPC visualized by particles of lead phosphate precipitate wasconsiderably increased when compared with the control. The band of lead phosphateprecipitate on the plasma membrane was intensified, widened and became continuous asconsequence of the precipitate increase. Also the plasmodesm between ICs and PPC showed a high density of lead phosphate precipitate. Under SD, the plasma membrane of SEs and ICsand the plasmodesm between ICs and ICs showed a lower density of lead phosphateprecipitate. Unlike SEs and ICs, ATPase activity was hardly observed on the plasmamembrane of CCs and PPC. These observations suggested that apoplastic transport based onthe driving of H+-ATPase on plasma membrane was easily affected by SD condition, and thenlead to a low photosynthetic substance accumulation in inferior grains.4The responses of ethylene biosynthesis to water deficit in flag leaves and its relations tophotosynthesis and photochemical efficiencyThermal images indicated that SD obviously increased the temperature of flag leaves,mainly due to the decrease in E under SD. The marked increases in both EER and ACCconcentration were observed under SD, which can be effectively reversed by exogenous Spdor AVG. Exogenous Spd or AVG to some extent decreased the temperature of flag leaves. Thestrongly decreased of PNand gsas well as the photo-damage of PSII under SD at14and21DPA were also observed. Ciwas reduced at7DPA, but slightly increased at14and21DPAunder SD, indicating that the decreased PNat7DPA might result from stomatal limitations,while its decrease at14and21DPA might be attributed to nonstomatal limitations.Correlation analysis suggested that EER and ACC showed negative relations tophotosynthesis and photochemical efficiency. Data obtained suggested that the effects of SDwere predominantly mediated by the increase in EER and ACC concentration, which greatlydecreased the leaves photosynthesis and photochemical efficiency. Application of Spd or AVGevidently decreased the EER and ACC concentration, and thus exhibited a positive influenceon the leaves photosynthesis and photochemical efficiency under SD.