Study On The Alleviating Mechanism Of The Inhibitory Effect Of Exogenous Dopamine On Phenylpropionic Acid Stress In Cucumber

Cucumber(Cucumis sativus L.)is one of the most important vegetable crops.Continuous cropping obstacles can inhibit the growth,reduce the yield,degrade the fruit quality,and cause serious diseases and insect pests.Continuous cropping obstacles has become one of the limiting factors of cucumber quality and high yield.Autotoxicity is the main cause of continuous cropping disorder,and phenylpropionic acid(PA)is the most important autotoxic substance in cucumber.Dopamineda can regulate plant growth,remove reactive oxygen species,and improve plant stress resistance.Therefore,it is of great significance to study the effect of dopamine on cucumber growth under phenylpropionic acid stress.Cucumber,the main vegetable crop,was taken as the research object in this experiment,‘Jinyou 1’which have strong resistance to continuous cropping and‘Jinyan4’which have week resistance to continuous cropping was used as the experimental material,3-phenylpropionic acid was used to simulate the autotoxic substances,dopamine was used as the mitigation reagent,and root irrigation was used as the treatment methodto study the effects of exogenous dopamine on seed,seedling and fruit quality of cucumber under phenylpropionic acid stress.The research results are as follows:1.Phenylpropionic acid stress can reduce the germination rate of cucumber seeds,reduce the growth index,the bulge at the radicle of seeds,increase the content of electrolyte permeability and MDA,decrease the content of soluble sugar and increase the content of starch.Exogenous dopamine can alleviate these phenomena and improve the ability of seed growth.2.Phenylpropionic acid stress can inhibit the growth ability of cucumber seedlings,and reduce the chlorophyll content,chlorophll fluorescence parameters and photosynthetic capacity,and the experssion levels of chlorophyll biosynthesis related genes CHLH、HAMA1、POR and CAO were down-regulated,and the inhibition effect of ’Jinyan 4’ which has poor resistance is more obvious,and exogenous dopamine can alleviate this adverse effect.3.Exogenous dopamine could reduce the relative conductivity and the increase of malondialdehyde content of the two cucumber varieties under phenylpropionic acid stress,further enhance the accumulation of proline content in cucumber seedlings,and enhance the osmotic regulation ability of cucumber seedlings.The superoxide dismutase(SOD)activity of ’Jinyou 1’ was inhibited,but the SOD activity of ’Jinyan 4’ increased,The peroxidase(POD)activity of both cucumber seedlings increased,and the increase of ’Jinyou 1’ was more obvious,the activities of superoxide polyphenol oxidase(PPO),catalase(CAT)and ascorbate peroxidase(APX)were inhibited,and the activities of CAT and APX in ’Jinyan 4’were more severely inhibited.Dopamine could alleviate this adverse effect and enhance the antioxidant capacity of two cucumber seedlings,and the activities of POD,PPO,CAT and APX of two cucumber varieties were all increased.4.Phenylpropionic acid stress suppresses the cucumber seedling nitrogen assimilation ability,two varieties of cucumber glutamate dehydrogenase(GDH),glutamine synthetase(GS)and glutamate synthase(GOGAT)activity decreased,and nitrogen metabolism related enzyme activity of ’Jinyan 4’decline is more serious,applied dopamine can promote two varieties of cucumber nitrogen assimilation ability,related enzyme activity are rising.5.Under phenylpropionic acid stress,the activities of sucrose synthase(SS),sucrose phosphorylase(SPS)and acid invertase(AI)of two cucumber cultivars were increased,and the activities of these enzymes could be further enhanced by the application of dopamine.Neutral invertase(NI)activity was inhibited by phenylpropionic acid stress,and this phenomenon was alleviated by the application of dopamine.6.Under phenylpropionic acid stress,the endogenous dopamine content of cucumber cultivars increased,and the increase of ’Jinyou 1’ was more obvious.Exogenous dopamine could inhibit the secretion of endogenous dopamine in cucumber cultivars of both cultivars,leading to the decrease of endogenous dopamine content.7.Phenylpropionic acid stress can reduce the content of various elements in cucumber,reduce fruit quality and yield,and produce deformed fruits.Exogenous dopamine can alleviate these phenomena,improve the appearance quality and yield of cucumber,and reduce deformed fruits.To sum up,the styrene acrylic acid stress will lead to the growth of cucumber seeds,seedlings and fruit ability is reduced,andthe inhibition of’Jinyan4’ was more serious,exogenous dopamine can relieve stress,reduce the accumulation of reactive oxygen species,improve oxidation resistance,enhance the photosynthetic capacity,promote metabolism of carbon and nitrogen metabolism related enzyme activity,promote the element absorption of cucumber,improve fruit quality and yield.