Effects Of Exogenous Sucrose On The Growth And Physiology Of Pumpkin Seedlings Under Low Light

Pumpkin（Cucurbita moschata Duch.）is an annual herb belonging to the genus Pumpkin in the family Cucurbitaceae,which first originated in South America and is one of the important traditional vegetable crops in China.In early spring season,pumpkin seedlings generally conducted in insulation facilities,in the southern region,often suffer from rainy weather more,by the time of sunlight and light intensity is significantly insufficient.Pumpkin seedlings are in a low light environment for a long time and their quality is reduced.Currently,artificial light supplementation measures are generally used to meet the light requirements of seedlings,but artificial light supplementation has the disadvantages of large equipment investment and high energy consumption.Studies have shown that sucrose plays an indirect or direct role by acting as a metabolic substrate or signal when plants are stressed.To this end,in this experiment,based on previous studies,the effects of exogenous sucrose（1%concentration is selected,and previous published studies have shown that spraying 1%sucrose is more effective than 2%and 3%sucrose）spraying on pumpkin and its morphological indexes,photosynthetic characteristics,light response curve,antioxidant system,content of various compounds of carbon and nitrogen metabolism and their related enzyme activities were investigated by simulating low light stress(the light intensity is 150μmol-m^-2-s^-1,and the normal light is 300μmol-m^-2-s^-1)in an artificial climate incubator,and the effects of sucrose on The physiological response mechanism of sucrose to the damage of low light stress in pumpkin was investigated in order to provide a reference for the cultivation of crop seedlings.The main findings are as follows:1.Under low light stress,the plant height stem thickness,biomass,robustness index and specific leaf weight of pumpkin seedlings increased significantly after 1%sucrose was sprayed on the leaf surface.The results indicated that the appropriate concentration of sucrose could alleviate the growth inhibition of pumpkin seedlings by low light to a certain extent,which was beneficial to maintain the structural integrity and functional stability of the leaves.2.Foliar spraying with 1%sucrose under low light significantly increased chlorophyll content,increased Pn,F_v/F_m andΦPSⅡ,and promoted specific activity and energy partitioning.It indicates that spraying exogenous sucrose can effectively increase chlorophyll content and increase the absorption transfer and conversion of light energy in pumpkin seedlings under low light conditions,and it can also help to alleviate the damage of PSⅡreaction center in pumpkin leaves by low light,increase the electron opening ratio of PSⅡreaction center,improve the efficiency of electron transfer and conversion of light energy,and reduce the degree of heat dissipation.3.Foliar spraying with 1%sucrose under low light significantly increased the activities of SOD,POD,CAT,APX and GR,increased the ability to scavenge O₂.^-and H₂O₂,and reduced the content of MDA,mitigated the damage to cell membrane and photosystem by low light stress,and promoted seedling growth.4.Foliar spraying with 1%sucrose under low light significantly increased the activities of carbon metabolizing enzymes（SS,SPS）and nitrogen metabolizing enzymes（NR,GOGAT,GDH,GS）,reduced the content of sucrose,fructose,amino acids and nitrate in mesophyll cells,and increased the content of starch and soluble protein.It can be seen that exogenous sucrose can regulate the activity of enzymes related to carbon and nitrogen metabolism under weak light stress,maintain the balance of synthesis and decomposition of organic compounds in plants,and enhance plant resistance.