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

Lesław B Lahuta,Marcin Horbowicz,Ewa Gojło,Ryszard J Górecki,Joanna Goszczyńska

doi:10.5586/asbp.2005.037

Lesław B Lahuta, Marcin Horbowicz + Show 3 more

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https://doi.org/10.5586/asbp.2005.037

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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 (Vicia hirsuta [L.] S.F. Gray). Immature seeds during 6-day incubation with D-chiro-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-chiro-inositol, and subsequent slow desiccation process caused accumulation of free cyclitol only, without biosynthesis of its galactosides. Feeding D-chiro-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-chiro-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.

Highlights

Raffinose family oligosaccharides (RFOs) comprises: raffinose, stachyose, and verbascose, containing 1, 2 and 3 galactosyl moieties in a molecule, respectively
Accumulation of raffinose family oligosaccharides (RFOs) and galactosyl cyclitols in vetch seeds matured on plants At the initial development stages of tiny vetch seeds, sucrose (Fig. 2A), myo-inositol and D-pinitol (Fig. 2B) were quantitatively main carbohydrates, and at 8 day after flowering (DAF) their concentrations were 35, 16 and 8 mg g-1 DW, respectively
Accumulation of raffinose family oligosaccharides (RFOs) and galactosyl pinitols began at 14-16 DAF and continued to seed maturity (Fig. 2C, D)

Summary

Introduction

Raffinose family oligosaccharides (RFOs) comprises: raffinose, stachyose, and verbascose, containing 1, 2 and 3 galactosyl moieties in a molecule, respectively. Beside RFOs, seeds of many species contain a-galactosides of myo-inositol, D-pinitol, D-chiro-inositol, D-ononitol and Abbreviations: RFOs raffinose family oligosaccharides; Gal-C a-galactosides of cyclitols; GolS galactinol synthase; FB1S fagopyritol B1 synthase; RS raffinose synthase; STS stachyose synthase; fagopyritols a-galactosides of D-chiro-inositol; GPA galactopinitol A; GPB galactopinitol B; DGPA di-galactopinitol A (ciceritol); TGPA tri-galactopinitol A; DAF day after flowering; FW fresh weight; DW dry weight. D-bornesitol (Yasui et al 1987; Horbowicz and Obendorf 1994; Peterbauer and Richter 1998; Lahuta et al 2001; Obendorf et al 2005).

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