Inhibition of raffinose family oligosaccharides and galactosyl pinitols breakdown delays germination of winter vetch (Vicia villosa Roth.) seeds

Abstract

Beside RFOs, which are commonly present in legume seeds, seeds of some species contain galactosyl pinitols (GPs). These carbohydrates, like RFOs, have been hypothesized to constitute an important energy and carbon skeletal source during germination. To test this hypothesis we have applied a specific α-galactosidase inhibitor (1-deoxygalactonojirimycin, DGJ) to germinating winter vetch (Vicia villosa Roth.) seeds, containing more galactosyl pinitols than RFOs. The breakdown of RFOs but not that of GPs was completely blocked in both embryonic axes and cotyledons tissues, during the first 18 h of imbibition in DGJ. The inhibitor only decreased the rate of GPs degradation. The inhibitory effect of DGJ on GPs degradation was partially alleviated by addition of sucrose or galactose to DGJ solutions. After three days of germination in water, RFOs and GPs disappeared in axial tissues of seeds imbibed in water, galactose or sucrose. Eighteen-hour imbibition of seeds in DGJ drastically reduced germination, by ca 50%, during the first three days. The inhibitory effect of DGJ decreased during the next seven days of germination. The presence of galactose or sucrose in imbibition solution initially stimulated seed germination, but later this effect was not statistically significant. Our study provides clear evidence that galactosyl pinitols play an important role in early winter vetch seeds germination. Additionally, we suggest that galactosyl pinitols can replace RFOs as reserve material necessary for early germination.