Dicyclohexylcarbodiimide and disodium succinate regulate the pulp softening and breakdown in fresh longan by modulating the metabolism of cell wall polysaccharides

Abstract

Cell wall polysaccharides (CWP) are an important component of cell structure, and its content variation is a primary factor affecting the texture of fresh longan. The influences of dicyclohexylcarbodiimide (DCC) and disodium succinate (DS) treatments on the pulp softening and pulp breakdown, and their relation to CWP metabolism in pulp of longan fruit were explored. Compared with the control longan, DCC-treated fruit showed lower value of pulp firmness, higher index of pulp breakdown, higher expression levels of cell wall disassembly enzymes (CWDEs)-related genes (DlPME1, DlPME3, DlPG1, Dlβ-Gal1, Dlβ-Gal16, DlCx7, DlXET3, DlXET27), and higher activities of CWDEs including pectin methyl esterase (PME), polygalacturonase (PG), β-galactosidase (β-Gal), cellulase (Cx), xyloglucan endotransglycosylase (XET), lower values of cell wall materials, and lower levels of CWP including ionic-soluble pectin, covalent-soluble pectin, cellulose, and hemicellulose. Whereas, the opposite effects were exhibited in DS-treated fruit. The above data indicate that DCC-hastened longan pulp softening and pulp breakdown was due to the up-regulating expressions of CWDEs-related genes, the activating activities of CWDEs, and the accelerating CWP disassembly by DCC treatment. Whereas, DS repressed longan pulp softening and pulp breakdown through down-regulating the expressions of CWDEs-related genes, inhibiting CWDEs activities, and reducing CWP degradation.