Anthocyanin concentration and antioxidant activity in light-emitting diode (LED)-treated apples in a greenhouse environmental control system

Abstract

Introduction. Anthocyanins are a group of flavonoids, and their synthesis is influenced by external and internal factors such as light, temperature, phytohormones and sugar concentration. A high anthocyanin concentration, which is related to redder coloration, is one of the factors of high-quality fruit. The effects of LED irradiation on the anthocyanin concentration and enzymatic and antioxidant activities in apple skin were studied. Materials and methods. Nine 8-year-old ‘Tsugaru’ apple trees (Malus domestica Borkh.) grafted onto Malling26 (M.26 EMLA) rootstocks planted in 45-L plastic pots covered with polyvinyl film (90% transmittance) and grown in a greenhouse were used. The effects of red or blue light-emitting diode (LED) irradiation on anthocyanin accumulation, the expression of MdMYB10 and UDP-glucose-flavonoid 3-O -glucosyltransferase (MdUFGT ) and superoxide anion radical (O scavenging activity in the skin of ‘Tsugaru’ apples were investigated under early heating cultivation in a greenhouse. Results and discussion. The anthocyanin concentrations in red LEDtreated apples were increased compared with those of the blue LEDtreated apples and the untreated control at 130 days after full bloom (DAFB). The relative expression of MdMYB10 and MdUFGT genes at 130 DAFB was also highest in the skin of apples treated with red LED light. The skin of apple fruits treated with red or blue LED light showed significantly low EC50 values. Conclusion. These results suggest that red LED irradiation may be used in a controlled environment such as a greenhouse to increase the anthocyanin synthesis and antioxidant activity in apple skin.