Photinia x fraseri “Red Robin” is known for producing young leaves that are red due to their high anthocyanin content. A number of postulates have been forwarded on the function of the red color but clear supporting evidence for them has not been shown. Since we observed that the color of emerging Photinia leaves can vary under different growth light environments and are darker red in open-grown plants, we hypothesize that the production of anthocyanin has a protective function against photoinhibition while the leaves are young, particularly in brighter environments.

Potted Photinia saplings were grown outdoors in 100% (HL) and 25% full sun (LL) for 2 months. Leaves from each plant were then measured for color change and anthocyanin concentration during development from first emergence to maturity (about 1 month later) at one-week intervals. Photo-protective functions were assessed by chlorophyll fluorescence. The amount of anthocyanin reflected the degree of redness with HL plants showing a rapid increase in anthocyanin peaking at 14 days after emergence while those in LL showed concentrations that increased moderately during development. Non-photochemical quenching only partially supported the protective function of anthocyanin in young leaves suggesting that it may play only a minor role in protection against photoinhibition during leaf development.