Quantitation of Toxic Steroidal Glycoalkaloids and Newly Identified Saponins in Post-Harvest Light-Stressed Potato (Solanum tuberosum L.) Varieties.

Although domesticated potatoes contain a large variety of steroidal glycoalkaloids (SGAs) and saponins, in the past, many research projects mainly focused on the two major SGAs, α-solanine and α-chaconine. This study investigates the quantitative changes, induced by post-harvest LED light exposure, of six SGAs and four saponins in 12 potato cultivars at three different time points (1, 7, and 16 days), by using ultra-performance liquid chromatography tandem mass spectrometry. Altogether, SGA contents of 3.0-17.1 mg/100 g fresh weight (FW) could be observed in the analyzed tubers with potato varieties highly exceeding the newly discussed safety limit of 10 mg/100 g. The overall contents of 0.1-5.4 mg/100 g FW of the so far barely studied saponins, like protoneodioscin or barogenin-solatrioside, highly differed between the assayed potato cultivars. Furthermore, cultivar-specific regulations of SGAs and saponins could be observed due to light exposure.

Steroidal Saponins─New Sources to Develop Potato (Solanum tuberosum L.) Genotypes Resistant against Certain Phytophthora infestans Strains.

Plant pathogens such as Phytophthora infestans that caused the Irish Potato Famine continue to threaten local and global food security. Genetic and chemical plant protection measures are often overcome by adaptation of pathogen population structures. Therefore, there is a constant demand for new, consumer- and environment-friendly plant protection strategies. Metabolic alterations induced by P. infestans in the foliage and tubers of six different potato cultivars were investigated. Using a combination of untargeted metabolomics, isolation techniques, and structure elucidation by MS and 1D/2D-NMR experiments, five steroidal glycoalkaloids, five oxylipins, and four steroidal saponins were identified. As the steroidal saponins showed antioomycete but no hemolytic activity, they may thus be considered as probably safe target substances for enrichment in breeding programs for disease resistance and as chemical lead structures for the production of nature-derived synthetic antioomycetes.

Biosynthesis of α-solanine and α-chaconine in potato leaves (Solanum tuberosum L.) - A 13CO2 study.

α-Solanine and α-chaconine are the major glycoalkaloids (SGAs) in potatoes, but up to now the biosynthesis of these saponins is not fully understood. In planta13CO2 labeling experiments monitored by nuclear magnetic resonance spectroscopy (NMR) and high-resolution mass spectrometry (HRMS) unraveled the SGA biosynthetic pathways from CO2 photosynthates via early precursors to the SGAs. After a pulse of ~ 700 ppm 13CO2 for four hours, followed by a chase period for seven days, specific 13C-distributions were detected in SGAs from the leaves of the labeled plant. NMR analysis determined the positional 13C-enrichments in α-solanine and α-chaconine characterized by 13C2-pairs in their aglycones. These patterns were in perfect agreement with a mevalonate-dependent biosynthesis of the isopentenyl diphosphate and dimethylallyl diphosphate precursors. The 13C-distributions also suggested cyclization of the 2,3-oxidosqualene precursor into the solanidine aglycone backbone involving a non-stereoselective hydroxylation step of the sterol a mixture of 25S-/25R-epimers of the SGAs.