Exogenously applied D-pinitol and D-chiro-inositol modifies the accumulation of α-D-galactosides in developing tiny vetch (Vicia hirsuta [L.] S.F. Gray) seeds

Abstract

In the present study we have investigated the effect of exogenous cyclitols on the accumulation of their galactosides and raffinose family oligosaccharides (RFOs), as well as on some enzymes important for their biosynthesis in seeds of tiny vetch (<em>Vicia hirsuta</em> [L.] S.F. Gray). Immature seeds during 6-day incubation with D-<em>chiro</em>-inositol (naturally does not appear in seeds of tiny vetch) were accumulated cyclitol and its galactosides (fagopyritols: B1 and B2). Short 4-hour incubation with D-<em>chiro</em>-inositol, and subsequent slow desiccation process caused accumulation of free cyclitol only, without biosynthesis of its galactosides. Feeding D-<em>chiro</em>-inositol to pods of tiny vetch induced accumulation of high levels of its galactosides (fagopyritol B1, B2 and B3) in maturing seeds. Similarly, feeding D-pinitol increased accumulation of its mono-, di- and tri-galactosides: GPA, GPB, DGPA and TGPA in tiny vetch seed. Accumulation of both cyclitols and their galactosides drastically reduced accumulation of verbascose. Inhibition of RFOs biosynthesis by elevated levels of free cyclitols suggests some competition between formation of both types of galactosides and similarity of both biosynthetic routes in tiny vetch seeds. Galactinol synthase (GolS) from tiny vetch seeds demonstrated ability to utilize D-<em>chiro</em>-inositol as galactosyl acceptor, instead of myo-inositol. Presence of both cyclitols, as substrates for GolS, caused synthesis of their galactosides: fagopyritol B1 and galactinol. However, formation of galactinol was more efficient than fagopyritol B1. D-chiro-Inositol and D-pinitol at concentrations several-fold higher than myo-inositol had inhibitory effect on GolS. Thus, we suggest that a level of free cyclitols can have an influence on the rate of galactinol biosynthesis and further accumulation of RFOs and galactosyl cyclitols in tiny vetch seeds

Phytic acid and raffinose series oligosaccharides metabolism in developing chickpea seeds

“…This data is supported by the fact that RFOs contents were positively correlated to the contents of inositol and sucrose but not the contents of galactinol (Karner et al 2004). Cyclic alpha-galactosides (Gal-C) along with RFOs are reported to be synthesized in developing seeds by the same route and same set of enzymes (raffinose synthase and stachyose synthase) (Lahuta et al 2005). So all these reports indicate galactinol synthase is probably not the only key enzyme which regulates the partitioning of carbon into RFO pool as previously thought.…”

Seed α-D-Galactosides of Selected Vicia Species and Enzymes Involved in Their Biosynthesis

“…2a-d). Similarly to earlier-investigated V. hirsuta, V. tetrasperma, soybean (Lahuta et al, 2005b(Lahuta et al, , 2005cObendorf et al, 2004;Gomes et al, 2005) and buckwheat (Ma et al, 2005), common vetch seed converted the D-chiro-inositol to galactosides (fagopyritols) much more effectively (Fig. 2d-f) than it converted D-pinitol to the corresponding galactosides ( Fig.…”

“…Indirect evidence for this hypothesis was found in developing seeds of two Vicia species -V. hirsuta (Lahuta et al, 2005b) and V. tetrasperma (Lahuta et al, 2005c) -and in soybean seeds fed with free cyclitols (Obendorf et al, 2004;Gomes et al, 2005). In vetch and soybean seeds, increased levels of D-pinitol and D-chiro-inositol enhanced accumulation of their galactosides and inhibited biosynthesis of RFOs.…”

“…In previous studies we introduced feeding of stem-leaf-pod explants with Dpinitol and D-chiro-inositol as an effective method for evaluating the regulatory role of cyclitols in galactoside biosynthesis in seeds of V. hirsuta (Lahuta et al, 2005b) and V. tetrasperma (Lahuta et al, 2005c). However, the seeds of those two species naturally accumulate D-pinitol and pinitol galactosides.…”

Cyclitols in maturing grains of wheat, triticale and barley

“…In seeds of various Vicia species, higher concentration of D-pinitol than that of myo-inositol throughout seed development and maturation coincides with accumulation of higher amounts of galactosyl pinitols and affects accumulation of RFOs. Feeding stem-pod-leaf explants of V. hirsuta and V. tetrasperma (Lahuta et al 2005b, c) with D-pinitol (naturally occurring in both vetch species) and D-chiro-inositol (not detectable in vetches) increased accumulation of appropriate galactosyl cyclitols and decreased accumulation of verbascose. Similarly, soybean feeding experiments with cyclitols showed competition between cyclitols and sucrose as primary galactose acceptors in RFOs and galactosyl cyclitols biosynthetic pathway (Gomes et al 2004;Obendorf et al 2004).…”