Physiological Responses Of Sugar Beet(Beta Vulgaris) Seedlings Pretreated With Allantoin To Saline-Alkaline Stress After Transplanting

Saline-alkaline land is a reserve cultivated land resource to be developed in our country,and its development is helpful to promote the sustainable development of agriculture.Sugar beet is a sugar crop with strong saline-alkaline tolerance.Research on how to enhance its saline-alkaline tolerance will help to increase the yield of sugar beet under saline-alkaline stress conditions,and can achieve the goal of developing and utilizing saline-alkaline soil resources to alleviate land conflicts.Purpose.In this study,3,6,and 9 m M allantoin foliar spray pretreatments were set up by vermiculite culture,respectively,to clarify the effectiveness of allantoin pretreatment on improving the salt-alkaline tolerance of sugar beet seedlings under saline-alkaline stress;here On the basis of this,a field test of sugar beet seedlings raised in paper tubes was carried out,and four allantoin concentrations of 1.5,3,4.5 and 6 m M were set to spray the leaves of sugar beet seedlings raised in paper tubes for pretreatment.The effects of bioaccumulation,photosynthetic fluorescence parameters,osmoregulation,antioxidant enzyme characteristics,endogenous hormone content,nitrogen metabolism and allantoin-related metabolism were exploring the physiological response mode of allantoin pretreated sugar beets to saline-alkaline stress after transplanting.The research results are as follows:Allantoin pretreatment can increase the dry-fresh weight and root-to-shoot ratio of sugar beet seedlings,effectively improve the photosynthetic parameters of leaves（net photosynthetic rate,stomatal conductance,and transpiration rate）,reduce intercellular CO₂ concentration,and improve chlorophyll fluorescence parameters（maximum photochemical efficiency,PSII actual electron yield,photochemical quenching coefficient）,reduce non-photochemical quenching coefficient,and improve seedling photosynthetic ability;after pretreatment,the content of osmotic adjustment substances（soluble sugar and soluble protein）in seedlings under saline-alkaline stress increases,and the antioxidant Enzyme activity increased,content of reactive oxygen species and malondialdehyde decreased;content of endogenous allantoin increased,activities of xanthine dehydrogenase,uric acid oxidase and allantoin synthase decreased,and activity of allantoinase increased,so that allantoin and allantoic acid in seedlings under saline-alkaline stress were accumulated.Field experiments found that with the increase of pretreatment allantoin concentration,the photosynthetic fluorescence index of sugar beet in saline-alkaline after transplanting showed a trend of increasing first and then decreasing;while the intercellular CO₂ concentration and non-photochemical quenching coefficient showed a trend of decreasing first and then increasing;relative chlorophyll（SPAD）value increased and the activity of Ru BP carboxylase was increased;the root-shoot ratio showed a trend of first increasing and then decreasing,and the optimization effect of 3 m M was more obvious in each treatment.After transplanting,the contents of soluble sugar and soluble protein in sugar beet roots and leaves showed a trend of first increasing and then decreasing with the increase of allantoin pretreatment concentration,and the activities of superoxide dismutase,peroxidase and catalase The increase of the pretreatment concentration showed a trend of increasing first and then decreasing;the change trend of MDA content in sugar beet leaves and roots was opposite to the above indicators,and the difference between 3 m M treatment and other treatments reached a significant level;after transplanting,IAA,CTK and GA content,and reduce the accumulation of ABA.This experiment found that with the increase of allantoin concentration,the contents of IAA,CTK and GA showed a trend of first increasing and then decreasing,and ABA showed a trend of first decreasing and then increasing.Obviously;allantoin pretreatment increased the activity of nitrogen metabolism enzymes in sugar beet leaves after transplanting,and the activities of sugar beet NR,GS and GOGAT enzymes showed a trend of first increasing and then decreasing with the increase of concentration,and 3 m M allantoin pretreatment could Significantly increased the activity of nitrogen metabolism enzymes in the leaves of sugar beet during the cluster growth period.The activities of xanthine dehydrogenase,urate oxidase and allantoin synthase in sugar beet transplanted to the field after pretreatment with exogenous allantoin were significantly increased,the activity of allantoinase was decreased,and the activity of uric acid,allantoin and allantoin It showed accumulation,and among the different treatments,the 3 m M treatment had the most significant effect on improving the salt-alkaline tolerance of sugar beets after transplanting.Different Allantoin pretreatment had different effects on the root yield and quality of sugar beet under saline alkaline stress.Pretreatment with 3 m M concentration could reduce the content of K⁺and Na⁺in sugar beetα-Compared with CK,the accumulation of amino nitrogen decreased by 32%,28%,and 16%,respectively.The root yield and sugar production increased by 12.6%and 16.9%,respectively,and the sugar content increased by 0.68 percentage points.