Abstract
Sunlight radiation is a main environmental factor which affects anthocyanin synthesis. To clarify the regulatory mechanism of sunlight on the synthesis of anthocyanin in apple peel, bagged apples were exposed to diverse intensities of sunlight through different shading treatments. Under an increased solar ultraviolet-B (UV-B) light intensity, the concentration of anthocyanin in apple peels was consistent with the Michaelis–Menten equation. Under lower sunlight intensities, diphenyleneiodonium chloride (DPI, an inhibitor of plasma membrane NAD(P)H oxidase) treatment increased both the concentration of cyanidin-3-glycoside and the activity of dihydroflavonol 4-reductase (DFR). However, under higher sunlight intensities, DPI treatment decreased the concentrations of cyanidin-3-glycoside and quercetin-3-glycoside, as well as the activities of DFR and UDP-glycose: flavonoid 3-O-glycosyltransferase (UFGT). These results indicate that, under low sunlight intensity, anthocyanin synthesis in apple peel was limited by the supply of the substrate cyanidin, which was regulated by the DFR activity. Nevertheless, after exposure to high sunlight intensity, the anthocyanin produced in the apple peel was dependent on UFGT activity.
Highlights
Apples are an important agricultural crop and anthocyanins are the visible sign of apple maturity [1]
At low temperature and under artificial UV-B conditions, MdbHLH3 binds to promoters of the anthocyanin synthesis genes MdDFR and MdUFGT to activate their expressions in apple fruit [25]
The apple fruits were exposed to different intensities of sunlight
Summary
Apples are an important agricultural crop and anthocyanins are the visible sign of apple maturity [1]. Anthocyanins act as visual signals to attract insects for pollination and agents for seed dispersal [4], and function as anti-oxidants, scavenging free radicals and protecting plant tissues against both biotic and abiotic stresses [5] These compounds have a positive effect on human health, serving as vasodilators and reducing the risk of myocardial infarction [6,7]. At low temperature and under artificial UV-B conditions, MdbHLH3 binds to promoters of the anthocyanin synthesis genes MdDFR and MdUFGT to activate their expressions in apple fruit [25]. Due to shading of the tree canopy, each fruit receives a diverse intensity of UV-B radiation With this variability, the structural genes which play important roles in the regulation of anthocyanin synthesis might be different. We analyzed anthocyanin biosynthesis in both ‘Fuji’ and ‘Red Delicious’ apples, treated with diphenyleneiodonium chloride (DPI) which is an NAD(P)H oxidase inhibitor that can restrained ROS to affect anthocyanin synthesis, upon exposure to diverse sunlight intensities, in order to gain further insights into the regulation of anthocyanin synthesis
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