Essentiality of nickel in plants: a role in plant stresses

Abstract

The element Ni is considered an essential plant micronutrient because it acts as an activator of the enzyme urease. Recent studies have shown that Ni may activate an isoform of glyoxalase I, which performs an important step in the degradation of methylglyoxal (MG), a potent cytotoxic compound naturally produced by cellular metabolism. Reduced glutathione (GSH) is consumed and regenerated in the process of detoxification of MG, which is produced during stress (stress-induced production). We examine the role of Ni in the relationship between the MG cycle and GSH homeostasis and suggest that Ni may have a key participation in plant antioxidant metabolism, especially in stressful situations.

Keywords: glutathione reductase; glyoxalase; methylglyoxal; nickel; oxidative stress.

Figure 1

Under normal physiological conditions, methylglyoxal (MG) is formed in plants during glycolysis and photosynthesis from dihydroxyacetone phosphate, which is catalyzed by triose phosphate isomerase to form glyceraldehyde 3-phosphate (Richard, 1993). The intermediate enediolate-P is formed in this reaction, which, after losing a phosphoryl group by beta-elimination, forms enol, which in turn is converted into MG. The reactions between the intermediate enediol and MG are non-enzymatic (blue arrows). The MG formed is eliminated by the sequential actions of glyoxalase I and II, in which the consumption and regeneration of reduced glutathione occurs.

Figure 2

Biosynthesis of GSH. Glu, glutamine; Cys, cysteine; Gly, glycine; γ-ECS, gamma-EC synthase; GSH-S, glutathione synthetase; GR, glutathione reductase.