Night temperatures affect fruit coloration and expressions of anthocyanin biosynthetic genes in 'Hongro' apple fruit skins

We analyzed the fruit skin coloration and expressions of anthocyanin biosynthetic genes to determine the effects of night temperature on ` Hongro' apple (Malus domestica Borkh.). Trees were grown under low night temperatures (LNT; 3 degrees C lower than the control) and high night temperatures (HNT; 3 degrees C higher than the control) for 2 months from July to August. LNT promoted an increase of the a* value and decreases of the L*, b*, and h degrees values in fruit skins, but HNT produced the opposite results. Anthocyanins accumulated in fruit skins with increasing days after full bloom. The anthocyanin biosynthesis was promoted by LNT, but inhibited by HNT. Quantitative real- time polymerase chain reaction analysis revealed that LNT increased the expressions of anthocyanin biosynthetic genes, MdCHS, MdF3H, MdDFR, MdANS, and MdUFGT, but HNT decreased them. These results suggest that temperatures at night affect anthocyanin accumulation in apple fruit skins by regulating expressions of the anthocyanin biosynthetic genes.