Interactions among chilling tolerance, sucrose degradation and organic acid metabolism in UV-C-irradiated peach fruit during postharvest cold storage

UV-C irradiation treatment has been demonstrated to be able to enhance chilling tolerance in peach (Prunus persica L. Batsch) during postharvest cold storage. Sugar and organic acid play central roles in plant metabolism. However, little is known about the relationships among chilling injury, soluble sugar and organic acid in peaches subjected to UV-C. In this study, peaches were irradiated with UV-C (1.5 kJ/m2) and then stored at 1 °C for 35 days. The content of sugar and organic acid, activities of enzymes, and the expression of enzyme genes that catalyze the metabolism of sugar and acid were evaluated. Results showed that UV-C significantly alleviated chilling injury and maintained the quality of peaches during storage. For sugar metabolism, UV-C suppressed sucrose degradation and glucose production mostly by inhibiting the enzyme activity and mRNA transcription of invertase (β-d-fructofuranoside fructohydrolase; EC 3.2.1.26) during the cold storage. For organic acid metabolism, UV-C irradiation downregulated the enzyme activities and gene expressions of aconitase (citrate hydrolyase; EC 4.2.1.3), and NADP-malic enzyme (S-malate: NADP-oxidoreductase; EC 1.1.1.40), but upregulated the enzyme activities and gene expressions of citrate synthase (acetyl-CoA: oxaloacetate C-acetyltransferase; EC 2.3.3.1) and NAD-malate dehydrogenase (l-malate: NAD-oxidoreductase; EC 1.1.1.37), leading to the low degradation of citric and malic acids during the whole storage periods. These results suggest that UV-C enhanced chilling tolerance in peach fruit during cold storage by suppressing the degradations of sucrose, citric, and malic acids.