Transgenic tobacco plants overexpressing glyoxalase enzymes resist an increase in methylglyoxal and maintain higher reduced glutathione levels under salinity stress

Abstract

The mechanism behind enhanced salt tolerance conferred by the overexpression of glyoxalase pathway enzymes was studied in transgenic vis-à-vis wild-type (WT) plants. We have recently documented that salinity stress induces higher level accumulation of methylglyoxal (MG), a potent cytotoxin and primary substrate for glyoxalase pathway, in various plant species [Yadav, S.K., Singla-Pareek, S.L., Ray, M., Reddy, M.K. and Sopory, S.K. (2005) MG levels in plants under salinity stress are dependent on glyoxalase I and glutathione. Biochem. Biophys. Res. Commun. 337,[61][62][63][64][65][66][67]. The transgenic tobacco plants overexpressing glyoxalase pathway enzymes, resist an increase in the level of MG that increased to over 70% in WT plants under salinity stress. These plants showed enhanced basal activity of various glutathione related antioxidative enzymes that increased further upon salinity stress. These plants suffered minimal salinity stress induced oxidative damage measured in terms of the lipid peroxidation. The reduced glutathione (GSH) content was high in these transgenic plants and also maintained a higher reduced to oxidized glutathione (GSH:GSSG) ratio under salinity. Manipulation of glutathione ratio by exogenous application of GSSG retarded the growth of non-transgenic plants whereas transgenic plants sustained their growth. These results suggest that resisting an increase in MG together with maintaining higher reduced glutathione levels can be efficiently achieved by the overexpression of glyoxalase pathway enzymes towards developing salinity stress tolerant plants.

Proline and Glycinebetaine Ameliorated NaCl Stress via Scavenging of Hydrogen Peroxide and Methylglyoxal but Not Superoxide or Nitric Oxide in Tobacco Cultured Cells

“…21,23) In the present study, both short-term and long-term NaCl treatment induced MG accumulation in BY-2 cells (Fig. 4A and B).…”

“…Four-d-old non-stressed cells were incubated with 50, 100, or 200 mM NaCl in the presence and the absence of 20 mM proline or betaine for 3 h on a rotary shaker at 100 rpm at 25 C in the dark. The MG content was measured by the method of Yadav et al, 23) with modifications. An aliquot of cells (0.5 g fresh weight) was homogenized in 2 ml of PBS.…”

“…[12][13][14][18][19][20] In plant cells, salinity also leads to the accumulation of methylglyoxal (MG), a cytotoxic compound that can react with and modify other molecules, including DNA and proteins. [21][22][23] Because of the highly cytotoxic and reactive properties of H 2 O 2 , O 2 À , NO, and MG, their concentrations must be kept under strict control. Plants possess antioxidant defense and glyoxalase systems to protect their cells against the damaging effects of H 2 O 2 , O 2 À , and MG. 13,19,22,23) Proline, besides functioning as an osmoprotectant, suppresses production of free radicals 1,6,11) and reactive oxygen species (ROS).…”

“…[21][22][23] Because of the highly cytotoxic and reactive properties of H 2 O 2 , O 2 À , NO, and MG, their concentrations must be kept under strict control. Plants possess antioxidant defense and glyoxalase systems to protect their cells against the damaging effects of H 2 O 2 , O 2 À , and MG. 13,19,22,23) Proline, besides functioning as an osmoprotectant, suppresses production of free radicals 1,6,11) and reactive oxygen species (ROS). 24,25) Our recent study indicated that both exogenous proline and betaine decrease H 2 O 2 accumulation induced by NaCl 12) and cadmium.…”

Up-regulation of antioxidant and glyoxalase systems by exogenous glycinebetaine and proline in mung bean confer tolerance to cadmium stress

“…The presence and characterization of both Gly I and II has been reported in many plants and the genes encoding these enzymes have been cloned and found to be regulated under various environmental conditions (Yadav et al 2005a, b;Veena et al 1999;Singla-Pareek et al 2006Fujita 2009, 2010). Overexpression of the glyoxalase pathway in transgenic tobacco and rice plants has been found to prevent an increase of ROS and MG under stress conditions by maintaining glutathione homeostasis and antioxidant enzyme levels (Yadav et al 2005b;Singla-Pareek et al 2006.…”