Cell wall modifications and ethylene-induced tolerance to non-chilling peel pitting in citrus fruit

Low temperatures inhibit the pectin degradation of 'Docteur Jules Guyot' pear (Pyrus communis L.)

The most remarkable characteristic of European pears is extremely perishable and difficult to store after postharvest softening. Low-temperature storage is one of the most commonly used methods to prolong the shelf life of European pears. However, the regulatory mechanism of the low-temperature delay of the softening of European pears is still unclear. In this study, the fruit firmness, pectin polysaccharide content, pectin-degrading enzyme activity, and pectin degradation gene expression of 'Docteur Jules Guyot' pears under low temperature (LT) and room temperature (RT) were analyzed. It was found that water-soluble pectin (WSP) was significantly negatively correlated with fruit flesh firmness, and the activities of several pectin-degrading enzymes were inhibited under LT storage conditions. In addition, it was also found that the gene expression patterns of PcPME2, PcPME3, PcPG1, PcPG2, PcPL, PcGAL1, PcGAL2, PcGAL4, and PcARF1 were inhibited by LT. The C-repeat binding factors PcCBF1 and PcCBF2 were also inhibited by long-term LT storage. Correlation analysis showed that the expression of PcCBFs was positively correlated with pectin-degradation enzyme genes, and we found that the promoters of many pectin-degradation enzyme genes contain the CRT/DRE motif, which CBF can directly bind. Therefore, it is speculated that long-term low-temperature conditions inhibit pectin degradation through PcCBFs.

Ozone-induced kiwifruit ripening delay is mediated by ethylene biosynthesis inhibition and cell wall dismantling regulation

Ozone treatments are used to preserve quality during cold storage of commercially important fruits due to its ethylene oxidizing capacity and its antimicrobial attributes. To address whether or not ozone also modulates ripening by directly affecting fruit physiology, kiwifruit (Actinidia deliciosa cv. 'Hayward') were stored in very low ethylene atmosphere at 0°C (95% RH) in air (control) or in the presence of ozone (0.3μLL(-1)) for 2 or 4 months and subsequently ripened at 20°C (90% RH) for up to 8d. Ozone-treated kiwifruit showed a significant delay of ripening during maintenance at 20°C, accompanied by a marked decrease in ethylene biosynthesis due to inhibited AdACS1 and AdACO1 expression and reduced ACC synthase (ACS) and ACC oxidase (ACO) enzyme activity. Furthermore, ozone-treated fruit exhibited a marked reduction in flesh softening and cell wall disassembly. This effect was associated with reduced cell wall swelling and pectin and neutral sugar solubilization and was correlated with the inhibition of cell wall degrading enzymes activity, such as polygalacturonase (PG) and endo-1,4-β-glucanase/1,4-β-glucosidase (EGase/glu). Conclusively, the present study indicated that ozone may exert major residual effects in fruit ripening physiology and suggested that ethylene biosynthesis and cell walls turnover are specifically targeted by ozone.