γ irradiation mediated the inhibitory effect of Ca2+ signals on softening of blueberry fruit during cold storage

Abstract

Postharvest blueberries tend to soften and rot, resulting in serious fruit waste. Gamma (γ) irradiation can delay the softening of blueberries and improve fruit quality. Calcium is a structural component of plant cell wall and membrane, and plays a role as a second messenger in the physiological process of fruit. To explore the mechanism of inhibiting the softening of cold storage blueberry fruit by γ irradiation, ‘Bluecrop’ blueberry fruit were treated by γ irradiation at a dose of 2.5 kGy, and then combined with calcium ion (Ca2+) inhibitors and intracellular calmodulin antagonists. The Ca2+ fluorescence signals, fruit firmness, protopectin and different soluble pectin contents, cellulose and hemicellulose contents, and hydrolase activities were detected. Results showed that irradiation induced Ca2+ release from intracellular calcium store to generate fluorescence signals. Irradiation mediated the Ca2+ signals to exert a positive effect on fruit firmness of blueberries during cold storage, for the degradation of protopectin and chelator-soluble pectin to water-soluble pectin was reduced by inhibiting activities of polygalacturonase and pectin methylesterase. Therefore, γ irradiation-induced Ca2+ signals played an important role in regulation of pectin-involved fruit softening in blueberries during cold storage. This study provides a theoretical basis for the mechanism of Ca2+ signaling in blueberry storage.