Mechanism Of 1-methylcyclopropene(1-MCP)in Relieving High Temperature Injury Of Cucumber And Pepper

Cucumber and pepper are common crops in the cultivation of vegetables in China,but the extreme high temperature caused by the rising global temperature frequently restricts the growth and development of cucumber and pepper.How to alleviate the adverse effects of high temperature stress on crop growth and yield is one of the focuses of agricultural scientists.1-methylcyclopropene?1-MCP?is a novel ethylene inhibitor,can participate in many physiological and biochemical reactions in plants,regulate plant growth and development,and respond to a variety of abiotic stresses.However,the current research of 1-MCP mainly focuses on improving the storage quality of horticultural products and extending the shelf life of the products.The mechanism for alleviating the high temperature damage of cucumber and pepper is rarely reported.Therefore,this paper uses artificial climate chamber to simulate high temperature environment,and studies the physiological and molecular mechanisms of foliar application of suitable concentration of 1-MCP to alleviate high temperature injury of cucumber and pepper seedlings;the mechanism of 1-MCP to increase crop yield and the optimum concentration are discussed by exploreing the effects of different concentrations of 1-MCP on the yield of cucumber and pepper in the autumn or winter.The main findings of this paper are as follows:1.Foliar application of 80 g·ha^-1 1-MCP could effectively alleviate the damage caused by high temperature stress on cucumber seedlings.Under high temperature stress,the growth of cucumber seedlings was severely inhibited,and the heat damage index was as high as 46.7.The spraying of 80g·ha^-1 1-MCP could significantly alleviate the high temperature injury of seedlings.Compared with the control,1-MCP treatment promoted the photosynthetic rate,total dry weight and root activity of the seedlings,which increased respectively by 12.7%,55.1%and 78.5%;the treatment with 1-MCP significantly inhibited MDA content,relative conductivity,H₂O₂ content,and O₂production rate under high temperature stress;increased antioxidant enzyme activities and osmotic adjustment substance contents to alleviate the damage caused by high temperature on plant cells;1-MCP treatment significantly reduced the content of abscisic acid and ethylene,the accumulation of senescent hormones,the key enzymes activities of ACS and ACO,and down-regulated the genes expression of ethylene receptors and related genes,thereby alleviating the damage caused by high temperature on cucumber seedling growth.2.Foliar application of 80 g·ha^-1 1-MCP could effectively alleviate the damage caused by high temperature stress on cucumber seedlings.Under high temperature stress,the growth of pepper seedlings was severely inhibited,and the heat damage index was as high as 60.5.The spraying of 80g·ha^-1 1-MCP could significantly alleviate the high temperature oxidation damage.Compared with the control,1-MCP treatment promoted the chlorophyll a content,chlorophyll b content,fresh weight,dry weight and root activity of the seedlings,which increased respectively by 27.1%,25.0%,56.4%and35.3%.It can significantly inhibited the increase of MDA content,relative conductivity,H₂O₂ content,and O₂production rate under high temperature stress,which respectively decreased by 48.4%,23.0%,54.9%and 71.1%.Moreover,1-MCP treatment promoted the antioxidant enzymes activities of SOD,POD and CAT to increase by 12.0%,44.4%and 125.8%,benefited the soluble sugar and soluble protein content to increase by 29.8%and 18.9%,thereby alleviating the damage caused by high temperature on the growth of pepper seedlings.3.Foliar application of 1-MCP two days before planting could promote the yield of cucumber in autumn-winter in the greenhouse.Foliar application of 20,80,160 g·ha^-1 1-MCP was beneficial to the growth and yield of seedlings after colonization.Among them,80 g·ha^-1 1-MCP was the best.On the one hand,foliar application of 80 g·ha^-1 1-MCP promoted plant height,leaf numbers,seedling index and photosynthetic rate of seedlings after planting,which was beneficial to the growth and development of cucumber seedlings;Application of 80 g·ha^-1 1-MCP could promote the opening of cucumber female flowers 2 days earlier,the yield per plant and the number per plant increased by 19.7%and 25.7%compared with the control,which were beneficial to increase the yield of cucumber in the greenhouse.The pre-term production,medium-term production,and the total output increased by 22.4%,29.5%,19.6%compared with control.4.Foliar application of 1-MCP two days before planting could promote the yield of pepper in autumn-winter in the greenhouse.Foliar application of 20,80,160 g·ha^-1 1-MCP was beneficial to the growth and yield after colonization.Among them,80 g·ha^-1 1-MCP was the best treatment.On the one hand,foliar application of 80 g·ha^-1 1-MCP significantly increased plant height,stem diameter,fresh weight,dry weight,and seedling index by 6.7%,9.9%,43.0%,41.0 and 38.4%;the content of chlorophyll a,chlorophyll b,carotenoid content,photosynthetic rate,stomatal conductance and transpiration rate respectively increased by 31.9%,40.5%,18.2%,18.8%,43.7%,21.9%compared with the control,and the intercellular carbon dioxide concentration decreased by 6.1%;on the other hand,foliar application of 80 g·ha^-1 1-MCP could promote the number of fruits per plant,yield per plant,pre-production,medium-term yield,later yield and the total output increased significantly by 12.8%,12.8%,13.0%,22.6%,9.2%,13.2%compared with control.