Abstract
Large amounts of caffeic acid esters accumulate in the vacuole of sweet potato cells in suspension culture. Their precursor, p-coumaroyl-Glc also accumulates in the vacuole. These findings suggest the possibility of vacuole to be a site for their esters biosynthesis. We previously showed that 3-hydroxylation of p-coumaroyl-Glc was catalyzed by polyphenol oxidase (PPO), whereas plant PPO is a chloroplast-localized enzyme, but not vacuole. In the present study, we examined the translocation of plastids into the vacuoles during biosynthesis of caffeic acid esters. 1) Forty-kD PPO occurred from plastid-localized 60-kD PPO by vacuolar protease. 2) Many structures speculated to be cytoplasmic components were observed in the vacuoles by electron microscopy. 3) Many MDC-staining structures are also observed in the cells, mainly in the vacuoles. These observations indicate that PPO-containing plastids are translocated into the vacuole during the biosynthesis of caffeic acid esters in sweet potato cells.
