| The apple industry in China is developing rapidly,with apple planting area and output accounting for more than 50%of the world’s.In the past five years,the national apple orchard area has remained at about 1.9 hm~2.However,there are still many problems in apple production.For example,the main apple varieties in China are relatively single,mainly Fuji.The single planting of apple varieties is likely to cause large-scale pests and diseases,especially apple canker.Dopamine is a kind of catecholamines.It has very important physiological functions in plants,such as participating in the removal of reactive oxygen species,participating in disease resistance,and interacting with hormones to affect plant growth and development.However,there are very few studies on dopamine regulating apple disease resistance.Therefore,in this study,M.hupehensis Rhed,GL-3 and MdTyDC overexpression apple plants were used as test materials.From the aspects of exogenous regulation of dopamine and endogenous synthesis and metabolism,pot experiment and in vitro inoculation of Valsa mail 03-8 were conducted to study the regulatory effect of dopamine on apple canker resistance,and to explore its possible mechanism of action.,and explored its possible mechanism of action.The scientific and effective prevention and control of apple canker in production has laid a theoretical foundation.The main findings are as follows:1.Using M.hupehensis Rhed as the test material,100μM dopamine was applied externally,and the leaves were inoculated with Valsa mail 03-8 for pre-experiment.It was preliminarily determined that exogenous dopamine could improve the resistance of apple leaves to apple canker.The results of the study showed that exogenous dopamine increased the activity of CAT,POD and SOD in leaves to eliminate the burst of reactive oxygen species caused by Valsa canker infection,and increased the expression levels of disease resistance-related genes Md PR1,Md PR2,Md PR5 and Md PAL in leaves.2.Using GL-3 as the test material,pot experiment and inoculation of Valsa mail 03-8were conducted to verify the regulatory effect of exogenous dopamine on apple disease resistance and explore its preliminary mechanism.The results of the study showed that dopamine,as a scavenger of active oxygen,can improve the antioxidant capacity of apple branches.Exogenous application of dopamine can reduce the peroxidative damage of Valsa mail by increasing the activities of SOD,CAT,POD and PPO in the branches.Exogenous application of dopamine increased the SA content and the expression of SA signaling pathway genes in apple branches.In addition,it can also increase the activity of defensive enzymes such as chitinase andβ-1,3-glucanase in the branches,and increase the content of chlorogenic acid,gallic acid,p-coumaric acid,epicatechin and the expression level of Md PAL in the branches to improve the resistance of apple to the disease.Using MdTyDC overexpression apple plants as test materials,they were inoculated with Valsa mail 03-8 to study the regulation effect of apple tyrosine decarboxylase gene MdTyDC on apple disease resistance.The results of the study showed that:MdTyDC responded to the infection of Valsa mail and after inoculation with Valsa mail,the dopamine content in the branches of the overexpressing MdTyDC plants was significantly higher than that of the wild type.Overexpression of MdTyDC increased the SA content and SA signaling pathway gene expression in apple branches.In addition,overexpression of MdTyDC also enhanced the activities of defense enzymes such as CAT,POD,PPO and chitinase in the branches,as well as the content of polyphenols such as gallic acid and chlorogenic acid in the branches,thereby enhancing the resistance of overexpression plants to Valsa mail. |
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