Promotive effects of 5-aminolevulinic acid on fruit quality and coloration of Prunus persica (L.) Batsch

Abstract

5-Aminolevulinic acid (ALA) is an essential precursor of all tetrapyrrole compounds in plants. Given its function as a regulator of plant growth, ALA has been widely applied to crops to enhance production. However, successful application of ALA to improve the fruit quality and coloration of Prunus persica (L.) Batsch has rarely been reported. The objective of this study was to investigate the effects of exogenous application of ALA on fruit quality and anthocyanin accumulation of fruit skin in P. persica. We measured the contents of vitamin C (Vc), soluble sugar, and titratable acid, the activity of antioxidant enzymes, and fruit mass. The content of anthocyanin in peach skin and the relative expression level of structural genes and transcription factor genes involved in anthocyanin synthesis were analyzed. Six-year-old peach trees were sprayed with 0 (control), 200, and 400mg/L ALA. Results showed that treatment with 200 and 400mg/L ALA significantly enhanced the contents of Vc and soluble sugar, the activity of antioxidant enzymes, and the ratio of soluble sugar to titratable acid in fruit flesh. In addition, the content of titratable acid in fruit flesh treated with 200 and 400mg/L ALA were significantly decreased relative to those in the control. However, ALA treatment did not affect fruit mass. The results of the qRT-PCR analysis indicated that the expression levels of six structural genes (CHS, CHI, F3H, DFR, LDOX, and UFGT) and two transcription factors (MYB10 and WD40) involved in anthocyanin biosynthesis were all significantly upregulated by ALA treatment. However, no significant difference was observed in the expression level of bHLH3 between the ALA-treated and control fruit skin. Taken together, our findings indicate that exogenous ALA treatment promotes fruit quality and anthocyanin accumulation in peach skin, and thereby enhances peach coloration by inducing the expression of key genes and transcription factors related to anthocyanin biosynthesis.