Polygalacturonase Levels Influence Electrolyte Efflux in Tomato Fruit

Abstract

Tomato fruit transformed with the PG-antisense gene have been shown to exhibit persistent structural competence and extended shelf-life compared with normal, PG-containing lines. In this study, PG-antisense and nontransformed, wild-type fruit were examined for electrolyte efflux trends during ripening and following extended storage at the full-ripe stage. Pericarp disks from PG-antisense fruit showed minimal differences in net electrolyte efflux compared with the normal, wild-type fruit at the mature-green through ripe stages of development. Following extended storage (14 days) of ripe fruit, or in response to storage at chilling (1°C) temperatures, significantly higher (25%–33%) values for proportional electrolyte efflux were observed for wild-type fruit. Additionally, ripe wild-type fruit following extended storage or in response to chilling injury exhibited increased (15%–20%) total soluble electrolytes, particularly in tissues subjected to freeze-thaw versus thermal-disruption. Although PG-antisense fruit do exhibit increases in net electrolyte efflux during ripening, the enhanced efflux and electrolyte generation from wild-type ripe fruit during extended storage was due, in part, to the release of polyelectrolytes originating from pectin hydrolysis. These data may explain the divergence in postharvest performance and structural integrity of PG-antisense and normal, wild-type fruit during post-ripe storage and also suggest that modification of the apoplastic environment resulting from developmental increases in electrolyte efflux can enhance the catalytic activity of PG in vivo.