Expression of a GALACTINOL SYNTHASE Gene in Tomato Seeds Is Up-Regulated before Maturation Desiccation and Again after Imbibition whenever Radicle Protrusion Is Prevented

Abstract

.)Raffinose family oligosaccharides (RFOs) have been implicated in mitigating the effects of environmental stresses on plants. In seeds, proposed roles for RFOs include protecting cellular integrity during desiccation and/or imbibition, extending longevity in the dehydrated state, and providing substrates for energy generation during germination. A gene encoding galactinol synthase (GOLS), the first committed enzyme in the biosynthesis of RFOs, was cloned from tomato (Lycopersicon esculentum Mill. cv Moneymaker) seeds, and its expression was characterized in tomato seeds and seedlings. GOLS (LeGOLS-1) mRNA accumulated in developing tomato seeds concomitant with maximum dry weight deposition and the acquisition of desiccation tolerance. LeGOLS-1 mRNA was present in mature, desiccated seeds but declined within 8 h of imbibition in wild-type seeds. However, LeGOLS-1 mRNA accumulated again in imbibed seeds prevented from completing germination by dormancy or water deficit. Gibberellin-deficient (gib-1) seeds maintained LeGOLS-1 mRNA amounts after imbibition unless supplied with gibberellin, whereas abscisic acid (ABA) did not prevent the loss of LeGOLS-1 mRNA from wild-type seeds. The presence of LeGOLS-1 mRNA in ABA-deficient (sitiens) tomato seeds indicated that wild-type amounts of ABA are not necessary for its accumulation during seed development. In all cases, LeGOLS-1 mRNA was most prevalent in the radicle tip. LeGOLS-1 mRNA accumulation was induced by dehydration but not by cold in germinating seeds, whereas both stresses induced LeGOLS-1 mRNA accumulation in seedling leaves. The physiological implications of LeGOLS-1 expression patterns in seeds and leaves are discussed in light of the hypothesized role of RFOs in plant stress tolerance.The raffinose family oligosaccharides (RFOs) are soluble galactosyl-Suc carbohydrates that constitute a significant component of phloem-transported sugars in some plants (Haritatos et al., 2000). Their accumulation in plants is associated with stressful environmental conditions such as cold, heat, or dehydration (Santarius, 1973; Santarius and Milde, 1977; Hinesley et al., 1992; Ashworth et al., 1993; Wiemken and Ineichen, 1993; Bachmann et al., 1994; Taji et al., 2002). The potential role of RFOs in stress tolerance has been intensively studied in seeds, particularly with respect to desiccation tolerance and longevity in the dehydrated state. RFOs are abundant in most mature desiccation-tolerant ("orthodox") seeds and are often rare or absent in "recalcitrant" seeds that cannot withstand desiccation (Lin and Huang, 1994; Sun et al., 1994). In seeds of many species, RFO accumulation coincides with the development of desiccation tolerance during seed maturation (Koster and Leopold, 1988; Leprince et al., 1993; Bewley and Black, 1994; Horbowicz and Obendorf, 1994; Black et al., 1996; Brenac et al., 1997a Brenac et al., , 1997b, and RFO content has been positively correlated with seed longevity in storage (Bernal-Lugo and Leopold, 1992; Horbowicz and Obendorf, 1994; Lin ...

Soybean physiology and gene expression during drought

“…GolS is a key enzyme in the production of raffinose-family oligosaccharides; it represents the galactynol from UDP-galactose and myoinositol, which serves as a precursor of galactosyl to form raffinose, stachyose and verbascose. Studies of A. thaliana have shown that the transcription factor DREB up-regulates expression of gols; accumulation of raffinose in plants is associated with tolerance of environmental stresses like cold and dehydration (Downie et al, 2003). However, in our study Gmgols gene expression was down-regulated in both genotypes.…”

Identification and Functional Characterization of the GALACTINOL SYNTHASE (MoGolS1) Gene in Melissa officinalis Plants

“…The transcription level of MoGolS1 gene also increased at moderate level in the leaves treated with cold for 12 h or 1 day. These data supported the findings of Taji et al [2002], who reported strong induction of AtGolS3 transcription when Arabidopsis plants were treated with cold for 10−24 h at 4 o C. Similar result was also reported by Downie et al [2003] mentioning that tomato galactinol synthase (LeGolS1) gene induction in the leaves of seedlings was maximum when treated with cold (5 o C) for 12 h. The transcription level of MoGolS1 gene after 2 days of cold treatment was weak and irregular (Fig. 6A).…”

“…Their accumulation in plants is associated with stressful environmental conditions such as cold, heat, or dehydration [Santarius, 1973;Santarius and Milde, 1977;Hinesley et al, 1992;Ashworth et al, 1993;Wiemken and Ineichen, 1993;Bachmann et al, 1994;Taji et al, 2002] when they presumably assist sucrose in ameliorating plant stress [Zhao et al, 2004]. It is also proposed to play significant roles in protecting cellular integrity during desiccation or dehydration and provides substrates for energy generation during seed germination [Downie et al, 2003].…”

“…Soluble sugars including raffinose family oligosaccharides (RFOs) have been implicated in mitigating the effects of environmental stresses on plants [Downie et al, 2003]. Their accumulation in plants is associated with stressful environmental conditions such as cold, heat, or dehydration [Santarius, 1973;Santarius and Milde, 1977;Hinesley et al, 1992;Ashworth et al, 1993;Wiemken and Ineichen, 1993;Bachmann et al, 1994;Taji et al, 2002] when they presumably assist sucrose in ameliorating plant stress [Zhao et al, 2004].…”

Galactinol and Raffinose Constitute a Novel Function to Protect Plants from Oxidative Damage

“…In knockout RS5 Arabidopsis mutants, the accumulation of raffinose was not observed during chilling stress (Zuther et al, 2004). In leaves of tomato (Solanum lycopersicum) and Arabidop-sis seedlings, the transcript levels of GolS and RS increased under environmental stress, such as cold and desiccation (Downie et al, 2003;Zuther et al, 2004). Arabidopsis contains seven genes that belong to the GolS family.…”