Effect of postharvest treatment of calcium and auxin on cell wall composition and expression of cell wall-modifying genes in the Chilean strawberry (Fragaria chiloensis) fruit

The effect of postharvest dips of CaCl2 and/or naphthalene acetic acid (NAA) on quality parameters, cell wall composition and expression of cell wall-modifying genes of Fragaria chiloensis fruits were evaluated. After treatments, the fruit was cold stored and samples were evaluated at 0 d, 5 d and after 8 d, plus 2 d at room temperature. No differences in firmness, acidity, and soluble solids content (SSC) were detected after cold storage between treatments. However, significant lower SSC levels were found in CaCl2- and NAA-treated fruits during cold storage, suggesting that these compounds could alter the normal breakdown of cell wall polysaccharides during postharvest. In this regard, CaCl2-treated fruit showed high contents of ionically-bound pectins and NAA-treated fruit exhibited low expression levels of endoglucanase gene (EG1) during cold storage. After cold storage, CaCl2, in combination with NAA, produced a reduction in the transcriptional level of polygalacturonase (PG1), pectate lyase (PL) and EG1 genes. In contrast, an increase in the expression levels of pectin methylesterase (PE1) and xyloglucan endotransglycosylase/hydrolase (XTH1) genes was observed after cold storage in CaCl2- and NAA-treated fruits, respectively. In conclusion, calcium and auxin could individually alter fruit ripening preventing the normal degradation of cell wall during cold storage, while the combination of calcium and NAA reduce significantly the transcript level of important cell wall degrading genes after cold storage, albeit no differences in firmness were recorded.