Exogenous Hemin Increases the Yield, Phenolic Compound Content, and Antioxidant Enzyme Activity of Dragon Fruit during the High-Temperature Period

Dragon fruits have abundant nutritional and antioxidant properties. High temperatures limit the growth and production of dragon fruits. Hemin can effectively alleviate abiotic stress in plants. However, the regulatory effect of Hemin on dragon fruit under heat stress remains unclear. In this study, we explored the impacts of foliar application of Hemin on dragon fruit size, yield and quality during the high temperatures of the summer season. In this experiment, dragon fruit variety ‘Jindu No. 1’ was used as material and treated with three Hemin concentrations, i.e., H1: 1 μmol.L−1, H2: 10 μmol.L−1, H3: 100 μmol.L−1, compared with CK: control. The results show that exogenous Hemin increased the single fruit weight, yield, fruit shape index and edible rate. It also improved pericarp L* value, a* value, C* and decreased ho, improving the peel colour; exogenous Hemin enhanced soluble solids content and phenolic compounds content and antioxidant enzyme activities in the pulp of dragon fruit. In addition, exogenous Hemin increased the content of chlorophyll content in dragon fruit stems. Differential metabolites determined by metabolomic assay also indicated that Hemin significantly increased the content of active substances such as selagin. Additionally, the Hemin treatment H2 also activated the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), which helps to mitigate the effects of high temperatures on dragon fruit. The current findings strongly advocate that H2 treatment may effectively counteract the adverse effects of heat stress by regulating the morph-physiological and antioxidant traits.