Effects Of Exogenous BR On Physiological Characteristics,Yield And Quality Of Sugarbeet Under Salt-Alkali Stress

The sugarbeet?Beta vulgaris L?.is a major plant of sugar industry,moreover it is able to bear the saline and alkaline.Saline-alkali stress reduced photosynthesis,yield,root tuber quality and economic benefit of sugarbeet.Brassinolide is an important plant growth regulator,which has a certain role in promoting the growth of sugarbeet.In the experiment,we used the variety KWS0143 as research object and added salt and alkali to barrel to simulate stress environment.In this way,we mainly studied the effects of BR spraying at different growth stages on photosynthetic characteristics,nitrogen metabolism enzyme activity,protective enzyme activity,secondary metabolites,endogenous hormone levels,dry matter accumulation and root tuber yield and quality of sugarbeet leaves.Determining the effects of BR spraying at different stages on physiological characteristics,yield and quality of sugarbeet to provide theoretical basis and technical reference for salt-tolerant cultivation of sugarbeet.The results are as follows:1.Spraying BR on June 25^th was selected in the earlier stage?rapid growth period of leaf cluster?,finding that chlorophyll and carotenoid contents in leaves increased,light absorption and protection ability strengthened,chloroplast morphology and structure were very stable,starch grains and autophagic vesicles were much lower than those of saline-alkali treatment.YII and q L increased in leaf cluster stage and sugar accumulation stage,decreased in root tuber expansion stage,decreased Y?NO?during the whole growth period,and increased electron transfer rate and active heat dissipation capacity of PSII.The activity of RUBP carboxylase increased significantly during the flourishing stage of leaves and the swelling stage of tubers.Spraying BR on August 1st was selected in the medium term?tuber swelling stage?.The results showed that chlorophyll and carotenoid contents decreased first and then increased,chloroplast structure remained intact partially,some of the stress was alleviated.These stacks of thylakoids keep partially intact,starch grains and autophagic vesicles decreased,YII decreased,q L increased,Y?NPQ?and Y?NPQ?/Y?NO?gradually increased,the activity of RUBP carboxylase was improved but not significant.Spraying BR on September 6^th was selected in the later stage?sugar accumulation period?.The content of chlorophyll and carotenoid in leaves increased slightly.And The mitigation effect of this method on chloroplast stress was not obvious.Only a small part of chloroplast structure was relatively complete,YII decreased significantly,q L,Y?NPQ?and Y?NPQ?/Y?NO?increased,Y?NO?decreased,and PSII's active heat dissipation ability increased.The activity of RUBP carboxylase increased significantly and exceeded that of normal treatment.2.After spraying BR at the early stage,the activity of NR increased significantly.While GS activity increased first and then decreased,repeating twice.After medium-term application of BR,the activities of NR and GS in leaves decreased first and then increased,but the increase was not significant.Later spraying BR,the activity of NR in leaves decreased significantly,while the activity of GS increased significantly.Spraying BR at different stages significantly inhibited GOGAT activity for a period of time.3.After spraying BR at the early stage,that promoted the synthesis of endogenous BR in leaves,and increased the contents of endogenous ABA,GA,CTK and IAA.This can improve the control ability of the blade.SOD activity and polyphenol content in leaves increased during the whole growth period,while POD activity and betaine synthesis rate increased during the vigorous growth period of sugarbeet.Compared with saline-alkali treatment,the content of MDA decreased significantly and the damage of membrane system was alleviated.After medium-term application of BR.The contents of IAA and CTK in leaves increased first,then decreased and then increased,while the contents of ABA,GA and BR showed the opposite trend.SOD and CAT activity decreased first and then increased,POD and APX activity decreased,betaine and MDA content decreased,polyphenol content increased.Later spraying BR,CTK content increased significantly,while BR and ABA content decreased.SOD activity increased,POD,CAT and APX activity decreased,polyphenol content increased,betaine and MDA content decreased.4.After spraying BR at different stages,the dry matter accumulation in the aerial part increased significantly.With the application time delayed,the effect on the sugar beet dry matter accumulation gradually decreased,and the earlier spraying BR had the most significant effect on the dry matter accumulation in the underground of sugar beet.Moreover spraying BR at different stages significantly increased sucrose content in beet tuber roots and decreased reducing sugar content.Pre-treatment significantly increased root yield,while mid-treatment and post-treatment significantly reduced the content of betaine and nitrate in root tuber,and improved root quality.5.In the treatment of superimposed BR spraying at different stages.The chlorophyll,IAA content and photochemistry quenching ability of leaves were increased by pre-treatment and mid-treatment,meanwhile the sucrose concentration was increased.Pre-treatment and post-treatment reduced the content of photosynthetic pigments,and the yield of root tuber was the highest.The concentration of sucrose was the highest,the content of betaine was the lowest and the quality was the best.