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Chilling injury (CI) is a major postharvest constraint in the long-term cold storage, transportation, and distribution of japanese plums (Prunus salicina). The aim of the work was to explain the development and severity of CI in japanese plums based on the oxidative stress theory following time course analysis of enzymatic and non-enzymatic antioxidants. Changes in membrane lipid peroxidation and enzymatic and non-enzymatic antioxidative systems in japanese plum cultivar Blackamber were determined at weekly intervals during 5 weeks of cold storage at 0 °C and at 2-day intervals during poststorage simulated shelf conditions (21 ± 1 °C) for 8 days after each week of cold storage. Fruit respiration and ethylene production rates showed typical climacteric patterns after removal from cold storage and these rates were relatively high after 4 and 5 weeks compared with 0 to 3 weeks of storage. The CI symptoms first appeared after 3 weeks of cold storage after fruit had been transferred to simulated shelf conditions. The incidence and severity of CI intensified with increasing storage duration. The extent of lipid peroxidation indicated by concentration of thiobarbituric acid-reactive substances and membrane damage manifested as electrolyte leakage increased with increasing duration of storage and subsequent simulated shelf conditions. Membrane lipid peroxidation exhibited positive correlation with the severity of CI. Activities of primary antioxidant enzymes and the enzymes involved in the ascorbate–glutathione cycle were determined to explain the levels of reduced and oxidized forms of cellular redox buffers, ascorbate and glutathione. In response to chilling stress, antioxidative protection systems operated efficiently during the first 3 weeks of cold storage, but extended storage resulted in loss of ability to ameliorate increasing levels of oxidative stress. In this study, the comprehensive analyses of various metabolites and antioxidative systems explain the series of events involved in development of CI in japanese plums in support of the oxidative stress theory.

Changes in endogenous free polyamines (putrescine, spermidine, spermine) were monitored from fruit set (fruit diameter 4.6 ± 0.5 mm, wt 0.09 ± 0.05 g) until 1 week before the expected harvest time in `Kensington Pride' and `Glen' to examine their role during mango (Mangifera indica L.) fruit development. Polyamines (PAs) in the pericarp tissues (exocarp and mesocarp) were estimated throughout the fruit development period, while estimations from growing ovules were started from 41 days after fruit set (DAFS). During fruit ripening, ethylene production and endogenous free PAs in skin and pulp of `Kensington Pride' mango were also monitored. PA contents of pericarp declined between fruit set and maturity from 788 to 101 nmol·g<sup>-1</sup> fresh weight (FW) in `Kensington Pride' and from 736.6 to 89.6 nmol·g^-1 FW in `Glen' during fruit development. Spermidine (SPD) and spermine (SPM) were higher than putrescine (PUT) during the initial phase of fruit growth. The highest levels of free PAs, especially SPD and SPM, at the initial stages of fruit growth suggest a potential role during the cell division phase and not in subsequent fruit development. Ovule seems to be a rich source of PAs as evident from 2.3- and 2.7-fold higher total PAs than pericarp tissues in `Kensington Pride' and `Glen', respectively. During fruit ripening of `Kensington Pride', total PAs increased in skin and pulp tissues along with the climacteric rise of ethylene, and reached maximum levels (skin 796, pulp 314 nmol·g^-1 FW) on day 4 of ripening. Skin exhibited 55.8% higher mean free PAs than the pulp. PUT dominated both in skin and pulp tissues. The simultaneous increase of ethylene and free PAs during fruit ripening suggests that their biosynthesis may not be competitive, and free PAs may have evolved as a response to increased biosynthesis of ethylene.