Effects of 5-Aminolevulinic Acid (5-ALA) on Physicochemical Characteristics and Growth of Pomegranate (Punica granatum L.)

Abstract

The pomegranate is one of the most essential crop fruits in the world. 5-Aminolevulinic acid (ALA) regulates the growth and development of 5-year-old pomegranate. However, for plenty of pome crops, conventional information on the physio-chemical characteristics underlying 5-ALA is limited. Therefore, in this study, we applied four different concentrations of 5-ALA treatments (0 mg L−1, 10 mg L−1, 20 mg L−1, 50 mg L−1, and 100 mg L−1), where 0 mg L−1 was considered as a control group, to evaluate the effects of 5-ALA on the physiochemical characteristics of pomegranates. Our results showed that maximal photochemical efficiency (FV/FM), photosystem (ΦPSII), and photochemical quenching (qP) increased at concentrations of 50 mg L−1 and 100 mg L−1 compared with controls. Anthocyanin contents were elevated by 2.27% and 1.33% at the 5-ALA concentrations of 50 mg L−1 and 100 mg L−1. Furthermore, qRT-PCRs of the DEGs, such as punica granatum chalcone synthase (PgCHS), chalcone isomerase (PgCHI), flavanone 3-hydroxylase (PgF3H), dihydroflavonol 4-reductase (PgDFR), anthocyanidin synthase (PgANS), and ultrafine-grained (PgUFG), showed up-regulations, except for chalcone isomerase (PgCHI), after 5-ALA treatments. The fresh weight of the fruit and the weight of the grains were elevated under 50 mg L−1 and 100 mg L−1 concentrations, and both the fresh weight of the fruit and the grain weight were higher than controls. Total sugar (TS) increased by 8.49% and 24.99%, total soluble solids (TSS) increased by 2.02% and 6.07%, soluble proteins increased by 1.16% and 1.15%, and the pH level of juice increased by 0.12% and 0.19%, respectively. In addition, the contents of ascorbic acid, total phenols, and total flavonoids increased by 24.18%, 2.53%, and 1.29%, respectively, compared with controls. Taken together, the antioxidant activities of SOD and POD also increased by 13.33% and 11.95% at concentrations of 100 mg L−1. Our results show that concentrations of 5-ALA treatments at 50 mg L−1 and 100 mg L−1 will be beneficial for crop cultivation.