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

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 ricMT 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 ricMT expression, and after Cd-induced ricMT expression. Rice suspension cells of sense- and antisense- ricMT transgenic lines were obtained by an Agrobacterium -mediated transformation. Overexpression of ricMT 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 MT -mediated tolerance of Cu and Cd toxicity in rice.