Regulatory Effect Of Spermidine On Saline-Alkaline Tolerance In Sugar Beet(Beta Vulgaris L.)

Sugar beet,one of the major sugar crops in China,has strong saline tolerance and can be used to exploit part of the saline soil,thus alleviating the conflict between cash crops and food crops for land,and to some extent promoting the development of China’s sugar industry.Therefore,it is important to study how to improve the salinity tolerance of sugar beet to grow sugar beet on saline soils,improve the yield and quality of sugar beet,fully exploit saline soils,and promote the healthy and sustainable development of ag riculture.Spermidine（Spd）can not only participate in seed germination and plant growth and development,but also significantly improve plant tolerance to abiotic stresses such as salinity,drought,low temperature and heavy metals.In this study,we inv estigated the effect of different Spd concentrations on improving the salinity tolerance of sugar beet by combining pot（Spd concentration range 0～1.5 m M）and field（Spd concentration range 0～0.9 m M）experiments with the saline soil conditions(EC 0.37 ds·m^-1)of the Songnen Plain and the salinity tolerance of sugar beet KWS1176 as the test material.The study investigated the effects of exogenous Spd on the growth,photosynthetic system,antioxidant system,nitrogen metabolism,polyamine metabolism,ho rmone content and yield and quality of sugar beet under salinity stress,to reveal the mechanism of Spd in regulating the salinity tolerance of sugar beet,and to provide theoretical basis and technical reference for further application of exogenous Spd on sugar beet.The results of the study are as follows:（1）Exogenous Spd increased the accumulation of dry matter of sugar beet under saline stress and promoted the growth of sugar beet leaves and tuber development.The results of the pot test showed that the dry matter accumulation was optimal when the Spd concentration was 0.3 m M,and the dry matter accumulation was not good or even unfavorable when the Spd concentration was 1.5 m M.The results of the field test and the pot test were consistent.Meanwhile,the exogenous Spd played a regulatory role in the photosynthetic system of sugar beet,increasing the net photosynthetic rate,transpiration rate and stomatal conductance,reducing the intercellular CO ₂ concentration,increasing the content of photosynthe tic pigments（chlorophyll a,chlorophyll b and carotenoids）,enhancing the activity of 1,5-diphosphate ribulose carboxylase,and improving the actual photochemical efficiency,maximum photochemical efficiency and photochemical burst coefficient of sugar be et leaves.Meanwhile,combined with pot and field tests,it was proved that the best promotion effect on photosynthetic indexes was achieved when the Spd concentration was 0.3 m M.（2）Exogenous Spd enhanced the activities of superoxide dismutase,peroxidase and catalase and weakened malondialdehyde in beet leaves and tubers under salinity stress;meanwhile,exogenous Spd enhanced the activities of nitrate reductase,glutamate synthase and glutamine synthetase in beet leaves under salinity stress;exogenous Spd regulated the contents of endogenous hormones in beet,enhanced the contents of growth hormone,cytokinin and The effect of Spd on endogenous hormones in sugar beet leaves was concentrated in the first and middle stages of growth,and the exogenous Spd spray had no significant effect on the content of growth hormone and gibberellin in sugar beet leaves in the later stages.Oxidase activity,and weakened the activities of spermidine decarboxylase,ornithine decarboxylase and polyamine oxidase,and the best promotion effect on total polyamines and polyamine-related enzymes was achieved when the Spd concentration was0.3 m M.（3）In field trials,exogenous Spd increased the yield of sugar beet tubers by 19.7%and the sugar content by 1.5 percentage points,while reducing the content of non-sugar substances（potassium salt,sodium salt andα-amino nitrogen）in sugar beet tubers,thus serving to improve the yield and quality of sugar beet.In conclusion,the foliar spraying of 0.3 m M Spd solution at the seedling stage of sugar beet had the best effect on promoting the growth and development of sugar beet under saline stress,increasing the yield,sugar content and sugar yield of sugar beet and inhibiting the accumulation of non-sugar substances in sugar beet tubers,thus improving the quality of sugar beet.