Exogenous dopamine improves apple fruit quality via increasing flavonoids and soluble sugar contents

Abstract Dopamine (DA) acts as a mediator in numerous plant physiological processes. In order to provide a basis for apple fruit quality improvements, we applied dopamine to apple trees via spraying (SDA) and watering (WDA). Five-year-old Changfu 2 (Malus domestica Borkh. cv. Naganofuji No.2) apple trees were treated with SDA or WDA in 0, 50, 100 and 200 μM. Results demonstrate that fruit fructose, sucrose and anthocyanin content, and ethylene production significantly increased for SDA100 and WDA100. Furthermore, the significant upregulation in WDA100 compared to WDA0 was observed for sugar transporter and flavonoid biosynthesis genes. Differential metabolite profiling analysis revealed the ability of flavonoids to distinguish between WDA0 and WDA100. Overexpression of the apple tyrosine decarboxylase gene MdTyDC in apple calli improved the dopamine and soluble content. This study demonstrates the role of dopamine as a regulator of the flavonoids and soluble sugar metabolism in improving apple fruit quality.