Sugar metabolism, chip color, invertase activity, and gene expression during long-term cold storage of potato (Solanum tuberosum) tubers from wild-type and vacuolar invertase silencing lines of Katahdin

Abstract

BackgroundStoring potato tubers at low temperatures minimizes sprouting and disease but can cause an accumulation of reducing sugars in a process called cold-induced sweetening. Tubers with increased amounts of reducing sugars produce dark-colored, bitter-tasting fried products with elevated amounts of acrylamide, a possible carcinogen. Vacuolar invertase (VInv), which converts sucrose produced by starch breakdown to glucose and fructose, is the key determinant of reducing sugar accumulation during cold-induced sweetening. In this study, wild-type tubers and tubers in which VInv expression was reduced by RNA interference were used to investigate time- and temperature-dependent changes in sugar contents, chip color, and expression of VInv and other genes involved in starch metabolism in tubers during long-term cold storage.ResultsVInv activities and tuber reducing sugar contents were much lower, and tuber sucrose contents were much higher, in transgenic than in wild-type tubers stored at 3-9°C for up to eight months. Large differences in VInv mRNA accumulation were not observed at later times in storage, especially at temperatures below 9°C, so differences in invertase activity were likely established early in the storage period and maintained by stability of the invertase protein. Sugar contents, chip color, and expression of several of the studied genes, including AGPase and GBSS, were affected by storage temperature in both wild-type and transgenic tubers. Though transcript accumulation for other sugar-metabolism genes was affected by storage temperature and duration, it was essentially unaffected by invertase silencing and altered sugar contents. Differences in stem- and bud-end sugar contents in wild-type and transgenic tubers suggested different compartmentalization of sucrose at the two ends of stored tubers.ConclusionsVInv silencing significantly reduced cold-induced sweetening in stored potato tubers, likely by means of differential VInv expression early in storage. Transgenic tubers retained sensitivity to storage temperature, and accumulated greater amounts of sucrose, glucose and fructose at 3°C than at 7-9°C. At each storage temperature, suppression of VInv expression and large differences in tuber sugar contents had no effect on expression of AGPase and GBSS, genes involved in starch metabolism, suggesting that transcription of these genes is not regulated by tuber sugar content.

Silencing of vacuolar invertase and asparagine synthetase genes and its impact on acrylamide formation of fried potato products

“…Thus, an acrylamide mitigation strategy focused on developing potato cultivars with low reducing sugars will likely be the most effective approach for minimizing the acrylamide-forming potential of French fry processing potatoes. However, it is less clear whether this variety development strategy also applies to chipping potatoes as these already have very low tuber reducing sugar contents, and VInv expression during postharvest storage may differ substantially from that in Russet Burbank (Wiberley-Bradford et al, 2014). Wild potato germplasm with extremely high level of CIS resistance is available (Hamernik et al, 2009).…”

UV-C treatment on physiological response of potato (Solanum tuberosum L.) during low temperature storage

“…CIS has been widely studied in potato tubers (Foukaraki et al 2016;Mehdi et al 2013;Wiberley-Bradford et al 2016), and it has been reported that CIS occurs due to an imbalance between the metabolism of starch and sugar (Ezekiel et al 2010). The degradation pathway from starch to hexoses is complex, and several enzymes are involved in this progress, including sucrose synthase (SuSy), sucrose phosphate synthase (SPS), ADP-glucose pyrophosphorylase small subunit (AGPase), granulebound starch synthase (GBSS) (Wiberley-Bradford et al 2014). Researchers proposed that the sucrose enters into the vacuole, where it can be cleaved to glucose and fructose, which was catalyzed by acid invertase (INV) (Sowokinos 2001).…”

Inhibition of Acrylamide Formation by Vanadium Salt in French Fries and Potato Chips

“…Generally, during cold induced storage, sucrose is converted to glucose and fructose by the vacuolar enzyme acid invertase (VInv) [31]. Therefore, harvesting time and storage condition greatly influence the levels of these reducing sugars.…”