Proline-mediated activation of glyoxalase II improve methylglyoxal detoxification in Oryza sativa L. under chromium injury: Clarification via vector analysis of enzymatic activities and gene expression.

Environmental factors affect plants in several ways including the excessive accumulation of methylglyoxal (MG), resulting in dysfunctions of many biological processes. Exogenous proline (Pro) application is one of the successful strategies to increase plant tolerance against various environmental stresses, including chromium (Cr). This study highlights the alleviation role of exogenous Pro on MG detoxification in rice plants induced by Cr(Vl) through modifying the expression of glyoxalase I (Gly I)- and glyoxalase II (Gly II)-related genes. The MG content in rice roots was significantly reduced by Pro application under Cr(VI) stress, however, there was little effect on the MG content in shoots. In this connection, the vector analysis was used to compare the involvement of Gly l and Gly II on MG detoxification in 'Cr(VI)' and 'Pro+Cr(VI)' treatments. Results exhibited that vector strength in rice roots increased with an increase in Cr concentrations, while there was a negligible difference in the shoots. The comparative analysis demonstrated that the vector strengths in roots under 'Pro+Cr(VI)' treatments were higher than 'Cr(VI)' treatments, suggesting that Pro improved Gly II activity more efficiently to reduce MG content in roots. Calculation of the gene expression variation factors (GEFs) indicated a positive effect of Pro application on the expression of Gly I and Gly ll-related genes, wherein a stronger impact was in roots than the shoots. Together, the vector analysis and gene expression data reveal that exogenous Pro chiefly improved Gly ll activity in rice roots which subsequently enhanced MG detoxification under Cr(VI) stress.