Expression of pigmentation genes and photo-regulation of anthocyanin biosynthesis in developing Royal Gala apple flowers

Abstract

Anthocyanin levels and the expression of six genes involved in anthocyanin biosynthesis (PAL, CHS, CHI, F3H, DFRand ANS) were studied during apple (Malus domestica Borkh.) flower development. In the petal, maximal accumulation of the six mRNAs occurred at an early stage of flower development and then declined rapidly following petal expansion. During petal development, the highest levels of CHI enzymatic activity and anthocyanin concentration appeared about one day after maximum mRNA levels of the six genes. Blocking UV or natural light (dark treatment) before flower bud break reduced the expression of the six genes and inhibited anthocyanin biosynthesis, resulting in either pink (UV block treatment) or pure white (dark treatment) apple flowers. Furthermore, the pure white flowers (dark treatment) were unable to resynthesise anthocyanins, even if they were re-exposed to light or placed under UV-B plus white light in vitrofollowing stage I of flower development. These results suggest that anthocyanin biosynthesis and the activities of these genes in the developing apple flower are controlled by both development and light and that the key stage for the photoregulation is during the early stages of development.