Electrical Stimulation as a Potential Technique for Enlarging Table Grape Berry Size by Enhancing Cell Division

Enlarging table grape berry size enhances commercial value. The texture and feel of large berries broken down in the mouth are important considerations for consumer purchase in East Asia. We report herein that electrical stimulation enlarges table grape berry size by enhancing cell division. Two field-grown grapevines cultivated in Yamanashi Prefecture, Japan, Shine Muscat and Pione, were exposed to electrical stimulation in two growing seasons using a solar panel from budbreak to harvest. Soluble solids content and total acid content in berries exposed to electrical stimulation were similar to those in untreated grapevines (control), whereas grapevines exposed to electrical stimulation had enlarged berry size irrespective of cultivar. Microscopic analysis of berry skins demonstrated that cell number per unit area of skin epidermis in grapevines exposed to electrical stimulation was higher than that of the control, suggesting that electrical stimulation enlarged berry size by enhancing cell division, but not cell elongation. This suggestion was supported by gene expression profiling of grape cultured cells exposed to electrical stimulation. Electrical stimulation upregulated the transcription of kinesin-like protein KIN-5C and nuclear pore complex protein NUP88, which regulate the cell cycle and cytokinesis, respectively, but not expansins, which play a role in plant cell elongation. One of the merits of exposing grapevine to electrical stimulation is that the electrical stimulation may reduce labor hours and load compared with other techniques, such as irrigation and girdling for berry enlargement. These findings could help in the development of a novel and innovative viticultural technique to enhance the commercial value of table grapes.