Abstract
Galactinol synthase (GolS), an enzyme synthesizing galactinol from myo-inositol and UDP-galactose, catalyzes the first step of the biosynthetic pathway of the raffinose family oligosaccharides (RFOs). A putative function of accumulated RFOs, galactinol and myo-inositol is compatible solute, but clear in vivo functions are uncertain. Six GolS genes were isolated from black poplar (Populus nigra ) leaves. We characterized expression patterns of the GolS genes in response to either drought, salinity, cold stress or abscisic acid (ABA) and found the distinct GolS gene of which transcript level remarkably increased in response to drought- and salt-stress (PnGolS2 ). The amounts of leaf raffinose, galactinol and myo-inositol were significantly larger in the poplar transformants overexpressing PnGolS2 (OXGolS) than those in non-transformants (NT). Leaf transpiration rate was significantly lower in the OXGolS plants than that in the NT due to the reduced stomatal conductance in the OXGolS. Leaf osmolality was unaffected by the overexpression of PnGolS2 while the leaf water potential showed more negative values in the OXGolS plants than that in the NT plants. These results suggest that overexpressing the drought and salt-responsive GolS gene, PnGolS2, reduces hydraulic conductance in black poplar.
