Relationship Between Proline and Hg2+-Induced Oxidative Stress in a Tolerant Rice Mutant

There has been little agreement regarding the mechanism by which proline reduces heavy metal stress. The present work examines the relationship between Hg2+-induced oxidative stress and proline accumulation in rice and explores the possible mechanisms through which proline protects against Hg2+ stress. The effect of proline on alleviation of Hg2+ toxicity was studied by spectrophotography and enzymatic methods. Hg2+ induced oxidative stress in rice by increasing lipid peroxidation. Pretreatment of the rice with 2 mM proline for 12 h profoundly alleviated Hg2+-induced lipid peroxidation and minimized H2O2 accumulation. Proline pretreatment significantly reduced (p < 0.01) the Hg2+ content in rice leaves. A comparison of the effects of proline pretreatment on H2O2 accumulation by Hg2+ and aminotrazole suggested that proline protected cells from Hg2+-induced oxidative stress by scavenging reactive oxygen species. The present work demonstrates a protective effect of proline on Hg2+ toxicity through detoxifying reactive oxygen species, rather than chelating metal ions or maintaining the water balance under Hg2+ stress.