Tissue distribution and changes in dopamine during development and stress responses in Malus germplasm

Dopamine is a catecholamine and an anti-oxidant which functions in responses to stress and it interacts with plant hormones to mediate plant development.  At present, there are few studies on the functions of dopamine in apple.  This study developed a method for dopamine determination which was used to analyze dopamine in Malus germplasm, in order to clarify the tissue distribution, developmental changes, diurnal variations, and stress responses in apple trees.  First, the proposed method was verified.  The linear range of quantification was robust from 0.1 to 20 ng mL^–1.  The instrumental, inter-day precision, and sample repeatability relative standard deviations were 1.024, 5.607, and 7.237%, respectively.  The spiked recovery was greater than 100%, indicating the feasibility of the method and its suitability for the rapid analysis of dopamine in Malus.  Next, the dopamine content was measured in 322 Malus tissues.  The results showed that the dopamine level in Malus was low and the average dopamine content in leaf was higher than in peel and flesh.  The dopamine had a skewed distribution that deviated to the right in cultivars and wild accessions.  Finally, the tissue specificity, developmental changes, diurnal changes, and responses to stress were analyzed.  In cultivar ‘Pinova’ (Malus domestica), the dopamine concentration was the highest in leaf buds and lowest in flesh.  The dopamine contents in leaf and flesh decreased with the growth and development of cultivar ‘Liangxiang’ (Malus domestica).  The dopamine content of apple leaves was higher after either drought or salinity stress as compared to the control.  In this study, a dopamine detection method for apple was established based on HPLC-MS and shown to be a robust approach.  This study provides a framework for future research on elucidating the tissue distribution, developmental changes, diurnal variation, and stress responses of dopamine in apple trees.