Effects Of Exogenous Selenium,Various Hormones And Their Interaction On The Cold Stress Resistance Of Tomato Seedlings

Cold stress is an important environmental factor affecting crop yield and geographical distribution.How to improve the resistance of crops to cold stress in production has attracted people’s attention.Among various research methods to improve the cold resistance of plants,the application of exogenous substances is a simple and effective important way.A large number of studies have shown that exogenous selenium application can effectively improve various environmental stress resistance of many plant organisms,but its mechanism of action is still unclear.Although studies on exogenous selenium on plant cold resistance have been reported,there are few studies on the effect of selenium on the cold resistance of tomatoes,especially there are few studies on the interaction between selenium and exogenous hormones,and further exploration is needed.The early experiments of this study mainly explored the effects of the interaction between selenium and exogenous hormones such as salicylic acid（SA）,melatonin（MT）,and abscisic acid（ABA）on the cold stress resistance of tomato plants,and further studied the effect and mechanism of exogenous selenium and SA and their interaction on improving the cold resistance of tomato seedlings under cold stress.The main findings are as follows:1.Under cold stress,tomato plants show symptoms of short plants and damaged leaves.Compared with the normal temperature control,low temperature led to a decrease in chlorophyll content,PSII maximum photochemical efficiency（Fv/Fm）,and damage to the cytoplasmic membrane.Exogenous selenium interactions with SA,MT,and ABA were all able to alleviate the damage caused by low temperature stress to tomato seedlings to some extent.However,compared with the Bi-care treatment,the co-application of selenium and SA had the best alleviation effect among the three complex treatments.while the interaction of exogenous selenium and SA enhanced the plant height,stem thickness,and root length of tomato seedlings under cold stress,increased relative water content of leaves,increased chlorophyll content,and increased Fv/Fm.2.Exogenous selenium interactions with SA,MT and ABA were all able to alleviate oxidative damage in tomato seedlings under low temperature stress to some extent,maintain the stability of the cytoplasmic membrane,which was manifested as reduced electrolyte leakage in the cytoplasm,reduced malondialdehyde（MDA）,and reduced the accumulation of reactive oxygen species in plants,such as hydrogen peroxide（H₂O₂）,superoxide anion(O^2-.)content reduction,and also reduced the activity of antioxidant enzymes POD,SOD and CAT.However,in comparison with the Biocare treatment,the co-application of selenium and SA was the most effective among the three combined treatments.The interaction between exogenous selenium and SA can reduce the content of reducing sugar,sucrose,and soluble total sugar,and reduce starch accumulation through the regulation of osmotic substances.It is hypothesized that exogenous selenium interactions with SA can effectively mitigate the damage caused by low temperature to tomato seedlings and alleviate oxidative damage,thus indirectly reducing the need for antioxidant enzymes in plants under low temperature stress.3.Exogenous selenium and SA interacted to induce the expression of five cold-induced related genes of PR1,ICE1,CYSb,LEA1 and Osmotin,thereby promoting the cold resistance of tomato seedlings.4.By applying SA synthesis inhibitor（2-aminoindan-2-phosphonic acid,AIP）to tomato seedlings under cold stress,it was found that the selenium and AIP treatment significantly reduced plant height,stem thickness,root length,chlorophyll content,Fv/Fm,and aggravated the oxidative damage of plants compared with the selenium treatment group.It can be seen that AIP can weaken the promotion effect of exogenous selenium on tomato seedlings under cold stress to a certain extent.This suggested that enhancing the cold resistance of plants by regulating the synthetic pathway of SA might be one of the mechanisms by which selenium enhanced the cold stress resistance of tomatoes.The above results showed that under cold stress,the interaction between exogenous selenium and SA could increase the chlorophyll content,increase Fv/Fm,effectively enhance photosynthesis,Mitigation of oxidative damage.The interaction between exogenous selenium and SA could also induce the expression of genes related to cold stress,improve plant cold tolerance,alleviate the stress degree of low temperature in plants,and promote plant growth.This study will help to elucidate the physiological and molecular mechanisms of selenium enhancing the cold resistance of tomatoes,thereby providing an important way to increase the yield of vegetables and other crops under cold stress,and also providing a theoretical basis for the application of selenium fertilizer in agricultural production.