Postharvest 24-epibrassinolide treatment alleviates pomegranate fruit chilling injury by regulating proline metabolism and antioxidant activities

Pomegranate fruit is susceptible to chilling injury (CI) during long term cold storage. In the current work, we studied the impact of pre-storage 24-epibrassinolide (24-EBL) application for CI amelioration of pomegranate during cold storage. The fruit were treated with 0, 5, 10 and 15 µmol L−1 24-EBL and stored for 84 d at 5 ± 1 ºC. Results showed that 15 µmol L−1 24-EBL treatment markedly alleviated CI, suppressed weight loss and reduced decay. Similarly, 15 µmol L−1 24-EBL application stimulated the activity of ornithine-δ-aminotransferase (OAT) and Δ1-pyrroline-5-carboxylate synthetase (P5CS) along with suppressed increase in proline dehydrogenase (PDH) enzyme which subsequently resulted in increased proline accumulation. The 15 µmol L−1 24-EBL treated pomegranate fruit had substantially lower activity of lipoxygenase (LOX) enzyme along with reduced concentrations of malondialdehyde (MDA), electrolyte leakage (EL), hydrogen peroxide (H2O2) and superoxide anion (O2•−) contents. In addition, 15 µmol L−1 24-EBL treated pomegranate fruit showed significantly higher activity of catalase (CAT), ascorbate peroxidase (APX), peroxidase (POD) and superoxide dismutase (SOD) enzyme in contrast with control. The 15 µmol L−1 24-EBL treated pomegranate fruit showed higher phenylalanine ammonia lyase (PAL) and had lower polyphenol oxidase (PPO) activity that subsequently resulted in conserved total phenols content. In the same way, pomegranate fruit treated with 15 µmol L−1 24-EBL had markedly higher total anthocyanins content, ascorbic acid and glutathione content as compared with control. It was also observed that 15 µmol L−1 24-EBL treated pomegranate fruit showed lower juice pH, higher titratable acidity (TA) and relatively lower soluble solids content (SSC) in contrast with control. In conclusion, 15 µmol L−1 24-EBL could be considered suitable for CI alleviation and quality maintenance of pomegranate fruit under cold storage.