The Regulation Of Exogenous EGCG On The Resistance Of Tomato Seedlings

Protected tomato is frequently subjected to various abiotic stresses,such as low temperature in winter and spring,high temperature and drought in summer,and secondary salinization caused by long-term continuous cropping and so on.In addition,the diseases and insect pests for tomato grown in the greenhouse are more serious than in the field.The occurrence of abiotic and biotic stresses seriously affected the yield and quality of vegetables and caused great economic losses.Flavonoid is one of the most important secondary metabolites for plants resist adverse ecological conditions,animals,microorganisms.Former studies revealed that flavonoid plays an important role in improving plant resistance to pests,low temperatures and diseases.In tea plant,catechins are the main components of flavonoid,and EGCG is the most important catechins in tea plant.In the present study,‘Hezuo 903'cultivar of tomato was selected to explore the effects of exogenous EGCG on tomato seeds germination and responses to biotic and abiotic stresses.The main findings are as follows:1.Under normal condition,there is no significant difference for the germination rate,germination energy and germination index of tomato seeds subjected to 10?M-200?M EGCG,while 500?M and 1000?M EGCG could significantly decrease the germination rate,germination energy and germination index of tomato seeds.Compared with the control,500?M EGCG could decrease three indicators by 2.6%,14.5%,7.4%respectively,and 1000?M EGCG could decrease by 6.6%,30.7%,15.6%respectively.2.EGCG could alleviate the inhibition of NaCl stress on tomato seeds germination.Under 150mM NaCl condition as salt stress,the germination rate,germination energy,germination index and the radicle length of tomato seeds are higher with 10?M-100?M EGCG treatment than that without EGCG.It is concluded that the best concentration of EGCG is 100?M and it can increase the germination rate,germination energy,germination index and the radicle length by 10.3%,15%,5.7,63.5%respectively.While200?M EGCG had no effect on seed germination and the radicle length.Furthermore,The inhibition on the germination and the radicle length of tomato seeds would be promoted under NaCl stress with 500?M and 1000?M EGCG.We also found that a large amount of ROS was produced in tomato seeds treated with 150mm NaCl,which led to the lipid peroxidation of cell membrane.Meanwhile,100?M EGCG could alleviate the inhibition of seed germination by promoting the antioxidant enzymes activity and scavenging excessive ROS.Compared with the control,100?M EGCG can scavenge 38.7%ROS and it can increase the activity of the APX and CAT by 60.7%and 26.8%respectively.3.EGCG could alleviate the damage caused by abiotic stresses such as low temperature,high temperature,salt and drought to tomato seedlings.We found that The Fv/Fm of 100?M EGCG under low temperature,high temperature,salt and drought was1.13,1.17,1.14,1.18 times as much as control,Meanwhile,large amounts ROS accumulated in the leaves of tomato seedlings under abiotic stresses,which cause damage for plant.100?M EGCG could reduce the damage to cell membrane and eliminate the excessive ROS by increasing the activity of antioxidant enzymes in tomato leaves.Further research confirmed that 100?M EGCG could accumulate H₂O₂ concentration in cell membrance by inducing NADPH oxidase.H₂O₂ plays an important role in promoting the antioxidant enzymes activity and scavenging excessive ROS,to improve the resistance for abiotic stresses in tomato plant.4.EGCG could improve the resistance of tomato seedlings to bacterial and fungal disease.Our study showed that 100?M EGCG pretreatment could not only inhibit the infection of Pst DC3000,and reduce the apoptosis in leaves,but also significantly alleviate the inhibition of photosynthesis of tomato leaves.The Fv/Fm becomes 1.2 times as much as the mock treated with 100?M EGCG.In addition,the lesion area of B.cinerea decreased significantly in vitro leaves pretreated with 100?M EGCG,compared with mock.At the same time,it was found that 100?M EGCG pretreatment could significantly reduce cell apoptosis and alleviate the photosynthesis inhibition caused by B.cinerea.The Fv/Fm becomes 1.2 times as much as the mock treated with 100?M EGCG.