H2O2 Is Involved in the Metallothionein-Mediated Rice Tolerance to Copper and Cadmium Toxicity

Abstract

Cadmium (Cd) and excess copper (Cu) are toxic to plants, causing a wide range of deleterious effects including the formation of reactive oxygen species. Metallothioneins (MTs) may protect plant cells from heavy metal toxicity by chelating heavy metals via cysteine thiol groups. They may also function as antioxidants. The study investigated the relationship of H₂O₂ production and <i>ricMT</i> expression in rice radicles and rice suspension cells under Cu or Cd stress. The results showed that H₂O₂ production in the rice radicles increased before Cu-induced <i>ricMT</i> expression, and after Cd-induced <i>ricMT</i> expression. Rice suspension cells of sense- and antisense-<i>ricMT</i> transgenic lines were obtained by an <i>Agrobacterium</i>-mediated transformation. Overexpression of <i>ricMT</i> significantly decreased the death rate of rice cells, which was accompanied by blocked H₂O₂ accumulation in rice suspension cells subject to Cu and Cd stress. Our findings confirm that H₂O₂ is involved in the <i>MT</i>-mediated tolerance of Cu and Cd toxicity in rice.