S23 - Session O3 - Metabolic changes in pomegranate fruit skin following cold storage promotes chilling injury of the peel

Authors: Idit Ginzberg *

Pomegranate cv. Wonderful fruit is susceptible to chilling injuries of the peel (CIp) when stored at 7 ºC. The damage manifested as superficial browning is restricted to the fruit skin, i.e., the outer colored layer of the peel; however, the affected skin becomes susceptible to pathogen invasion, increasing fruit waste. To characterize possible causes of CIp development, fruit were collected at early harvestmwhen the premature fruit is poorly colored and susceptible to CIp development, and at late harvestmwhen mature fruit has fully red skin. Skin samples were collected on the day of harvest and at different time points during storage. Anatomical study of skin with CIp disorder showed a broken cuticle layer with underlying degenerated cells. A high total phenol content, which is associated with high antioxidant capacity, was not sufficient to prevent the development of CIp in the premature fruit. The concentration of punicalagin was the same for premature and mature skin at harvest and during storage, and therefore not associated with CIp development in the premature fruit skin. Furthermore, the expression of antioxidant-related genes CATALASE 2 ( CAT2) , SUPEROXIDE DISMUTASE ( SOD), and GLUTATHIONE REDUCTASE 2 ( GR2) was similar for both premature and mature fruit skin. Poor pigmentation of the premature fruit skin and chilling-induced downregulation of key anthocyanin-biosynthesis genes were associated with CIp development. High total phenol concentration combined with high expression of the gene encoding POLYPHENOL OXIDASE ( PPO ) was also associated with CIp; however, a high expression ratio of PHENYLALANINE AMMONIA-LYASE ( PAL) to PPO may be associated with reduced CIp disorder. The results presented suggest future possibilities for controlling the CIp phenomenon.