Effects Of Exogenous 14-hydroxy Brassinosterol On Floret Development And Grain Setting Of Winter Wheat

To clarify the regulation mechanism of 14-hydroxy brassinosteroid(14-HBR)on spike floret development and grain setting of winter wheat under different water conditions,a multi spike variety Yumai 49-198(V1)and a large spike variety Zhoumai 16(V2)were used as experimental materials in 2018-2020.Irrigation(enough water)and no irrigation(middle drought)were set up 15 days before jointing.14-HBR(0.05 umol L-1)and water control were sprayed 20 days after jointing in each treatment.The effects of 14-HBR on fertile floret development,dry matter accumulation,soluble sugar content,nitrogen content and nitrogen accumulation dynamics,as well as photosynthetic carbon metabolism enzymes,nitrogen metabolism enzymes,antioxidant enzymes,osmotic adjustment substances,spike endogenous hormones,yield and its components of winter wheat were studied under irrigation and drought conditions.The main results are as follows:(1)Exogenous spraying of 14-HBR promoted the development of fertile florets,and increased the number of grains per spike and yield.Exogenous spraying of 14-HBR reduced the number of degeneration and abortion of fertile florets,and significantly increased the grain setting rate and spikelet setting rate and number of fertile florets.Under irrigation conditions,the number of fertile florets of the two varieties increased by 3.17(V1)and 4.54(V2)on average,and the number of grains increased by 3.45 and 4.42.The increase in grain setting was mainly concentrated in the strong central spike position and its nearby weak spike positions;drought under the conditions,the number of fertile florets of the two varieties increased by 5.04(V1)and 6.83(V2),and the number of grains increased by 3.83 and 4.71.The increase in grain setting was mainly reflected in the strong spike position in the middle,and the weaker spike position had little effect.Exogenous 14-HBR has little effect on the number of spikes and thousand-grain weight,and significantly increases the number of grains per spike,thereby increasing the yield.Under irrigation conditions,the yield of the two varieties increased by 9.31%(V1)and 12.03%(V2)on average,while the increase in drought conditions was as high as 18.33% and 24.02%,the increase in yield is mainly achieved by increasing the number of grains spike.In comparison,the control effect of exogenous 14-HBR on large-spike variety V2 is more obvious.(2)Exogenous 14-HBR could improve the accumulation and distribution of carbon and nitrogen assimilate in wheat under irrigation and drought conditions,but there are certain differences in the regulation effects of the two water conditions.Exogenous14-HBR increased the activities of Rubisco,SPS and SS metabolic enzymes in flag leaves,as well as the activities of nitrogen metabolism GS and NR enzymes,enhanced carbon and nitrogen accumulation and nutrient supply,increased spike C/N ratio,and increased spike carbon metabolism.The distribution of carbon and nitrogen between organs varies with water conditions.Under irrigation conditions,the exogenous 14-HBR increases the ratio of spike/non-organs.The nitrogen distribution under drought conditions is the same as that under irrigation,but the dry matter distribution is opposite;Exogenous 14-HBR increased the soluble sugar content and C/N ratio of the organs in the irrigation treatment,while the soluble sugar content and C/N ratio of the spikes in the drought treatment increased,but the leaves and stems decreased.Exogenous 14-HBR also increased the total soluble sugar ratio of wheat spike/stem,this is mainly due to the abnormality and accumulation of sugar metabolism in wheat plants caused by drought,and the exogenous 14-HBR promotes sugar metabolism and transportation.(3)Compared with drought treatment,exogenous 14-HBR increased the activities of SOD and CAT in wheat leaves;At the same time,exogenous 14-HBR increased the activity of pyrrole-5-carboxylic acid synthase(P5CS)and promoted proline.The synthesis of exogenous 14-HBR could also reduce the accumulation of MDA,and the contents of MDA in V1 and V2 decreased by 7.01 % and 9.44 % on average.Exogenous 14-HBR could also increase the water content of wheat organs.The water content of leaves,stems and panicles of V1 and V2 increased by 3.81 %,5.32 %,2.90 % and 3.89 %,4.94 %,2.51 %.Exogenous 14-HBR can enhance the ability of wheat to scavenge reactive oxygen species under drought stress,and promote the accumulation of osmotic regulator proline,increase plant water content,reduce MDA content,thereby enhancing the drought resistance of wheat under drought stress.These indicators did not change when spraying exogenous 14-HBR under irrigation conditions.(4)Drought can cause plant hormone metabolism disorders.Under drought stress,the endogenous ABA content of V1 and V2 cones increased,the contents of CTK,GA and IAA decreased,and the contents of CTK / ABA,GA / ABA and IAA / ABA decreased.Exogenous 14-HBR increased the contents of endogenous CTK,GA and IAA,and the ratios of CTK / ABA,GA3 / ABA and IAA / ABA.The correlation analysis showed that the CTK and GA contents of fertile spikelets at flowering stage were correlated with ABA content,correlated with ABA content,and not correlated with IAA content.The fertile spikelets were correlated with CTK / ABA,GA3 / ABA,and IAA / ABA.CTK,GA content is higher,IAA content is moderate,ABA content is lower,CTK / ABA,GA3 / ABA,IAA / ABA ratio is higher,more conducive to promoting panicle development.In summary,under irrigation and drought conditions,exogenous 14-HBR could improve the enzyme activity of Rubisco in flag leaves of winter wheat,increase the assimilation ability of CO2,improve the activity of carbon metabolism enzymes and the transport ability of soluble sugar to panicle organs,and ensure the supply of carbon assimilation.At the same time,14-HBR increased nitrogen metabolism enzyme activity and nitrogen supply in wheat,and provided enough nitrogen nutrition for spike development.Exogenous 14-HBR can also coordinate the endogenous of wheat spikes under two water treatments,increase the contents of IAA,CTK and GA,reduce the content of ABA,and increase the ratios of CTK / ABA,GA3 / ABA and IAA / ABA,thereby promoting the development and growth of spikelets.Under drought condition,exogenous 14-HBR can also reduce the effect of drought stress on wheat growth by increasing the activity of antioxidant enzymes and osmotic adjustment substances,maintaining the water content of plant,and providing a healthy guarantee for the accumulation and transportation of assimilates to the spike and the material supply of spike development.