Regulating Mechanism Of Low Night Temperature On Anthocyanin Metabolism In ‘Fuji’ Apple Peel

Temperature is one of the main factors that influence the metabolism of anthocyanins.Low temperature can improve anthocyanin synthesis and peel coloration by up-regulating the expression of related genes involved in anthocyanin biosynthesis. The present study focused on the mechanism of low night temperature on anthocyanin metabolism in ‘Fuji’ apple peel.Moreover, effects of exogenous ascorbate on anthocyanin accumulation were studied. These studies may provide an insight for improving apple color and quality.Bagged ‘Fuji’ apple fruits were used in this study. Metabolite concentrations, gene expressions, and enzyme activities involved in phenolics, active oxygen species, and ascorbate metabolism were assayed. The main results are as follow:1. Promotion of low night temperature on anthocyanin accumulation was closely related to the light intensity in the day. Anthocyanin concentration was higher at low night temperature(5°C and 15°C) than at 25°C in the peel of fruits shaded in the day with the sunlight intensity around 70%. However, when the fruits were exposed to the full sunlight in the day, the anthocyanin concentration was lower in fruits treated with low night temperatures.With 70% sunlight intensity in the day, the activity of UFGT was higher in the samples which were treated at low night temperature. Nevertheless, when the fruits were exposed to natural sunlight in the day, the enzyme activity of UFGT was higher at 25°C than at 5°C and 15°C at night. Therefore, low night temperature on the promotion of anthocyanin accumulation was mainly by increasing the activity of UFGT.2. Ascorbate can affect the anthocyanin accumulation in apple peel. Concentration of ascorbate was lower at 5°C in both 70% sunlight and natural sunlight in the day, but hydrogen peroxide concentration was higher at 5°C treated fruits. Exogenous application of ascorbate could enhance anthocyanin accumulation when fruits were treated in natural sunlight in the day. Besides, the higher the concentration of exogenous ascorbate, the more the contents of anthocyanin. When the sunlight intensity was 70%, there was no significant difference among different exogenous ascorbate treatments.In general, our results demonstrate that in natural sunlight conditions in the day, the low nigh temperature down-regulated the activity of UFGT via affecting the ascorbate metabolism,then decreased the anthocyanin concentration in ‘Fuji’ apple peel.