An overview on the role of methylglyoxal and glyoxalases in plants.

Methylglyoxal (MG) is a highly reactive cytotoxic alpha-oxoaldehyde compound and is formed endogenously via different enzymatic and non-enzymatic reactions. In plants MG is detoxified mainly via the glyoxalase system that is comprised of two enzymes, glyoxalase I and glyoxalase II. Glyoxalase I converts MG to S-D-lactoylglutathione by utilizing glutathione, while glyoxalase II converts S-D-lactoylglutathione to D-lactic acid, and during this reaction glutathione is regenerated. The presence and characterization of both glyoxalase I and II has been reported in many plants and the genes encoding these have been cloned and found to be regulated under various environmental conditions. In plants, MG has been found to be present during normal growth conditions and it accumulates to higher levels under various environmental stresses. Abiotic and heavy metal stresses induce reactive oxygen species (ROS) and MG. Overexpression of the glyoxalase pathway in transgenic tobacco and rice plants has been found to check an increase of ROS and MG under stress conditions by maintaining glutathione homeostasis and antioxidant enzyme levels. There is also evidence that in addition to glyoxalase, other pathways, such as the aldose reductase pathway, may also be involved in MG detoxification in plants. To unravel the role of MG and the glyoxalase pathway in signal transduction during environmental stress conditions in plants is a topic of future research interest. In this paper we review work on plant glyoxalases especially with respect to their role under abiotic stresses.