Seed desiccation tolerance and storability: Dependence on flatulence-producing oligosaccharides and cyclitols-review and survey

Stachyose, raffinose and related flatulence-producing oligosaccharides (alpha-galactosyl derivatives of sucrose) are associated with desiccation tolerance and storability of seed germplasm. Orthodox seeds of species with a sucrose-to-oligosaccharide ratio of < 1.0 have storability half-viability periods > 10 years while those > 1.0 have a storability halfviability period < 10 years. Seeds vary in their composition of oligosaccharides and some accumulate alpha-galactosyl derivatives of cyclitols. Known and proposed pathways for biosynthesis of soluble oligosaccharides, cyclitols and galactosyl derivatives of cyclitols are presented. Axes, cotyledons, embryos or seeds of 19 species in 7 families, (all orthodox seeds) were analysed for sucrose, galactosyl derivatives of sucrose, cyclitols and galactosyl derivatives of cyclitols by high resolution gas chromatography. Sucrose and myo-inositol are universally present and galactinol is present in seeds accumulating stachyose series oligosaccharides. Seeds of some species of Leguminosae accumulate mostly stachyose series oligosaccharides, whereas seeds of other species accumulate varying levels of galactosyl derivatives of cyclitols in addition. Castor bean (Euphorbiaceae) seeds accumulate galactinol and buckwheat (Polygonaceae) embryos accumulate galacto-chiro-inositol instead of the stachyose series oligosaccharides. The mass ratio of sucrose: non-sucrose is related to storability and is applicable to seeds accumulating cyclitol derivatives. Galactinol and galacto-chiro-inositol are proposed to function in the same role as raffinose and stachyose in facilitating desiccation tolerance and storability.