Growth and metabolic responses of maize (C₄ species) and rice (C₃ species) genotypes to cadmium toxicity

Toxic metals such as cadmium (Cd) are detrimental for growth of the crops. The differential sensitivity of maize and rice, the two vital cereals, which also belong to C4 and C3 plant types, respectively, to a similar degree of Cd stress is not known that comprised the objective of this study. Maize and rice genotypes were grown hydroponically in the presence of 5 and 10 μM cadmium (Cd) concentrations to examine their relative sensitivity to this metal at growth and metabolic levels. The shoots of maize genotypes accumulated relatively greater cadmium than those of rice while the roots of both the plant types did not differ significantly in cadmium accumulation. The shoots and roots of maize genotypes showed higher growth than rice genotypes under both Cd levels. At similar Cd level, the rice shoots showed greater damage to membranes and chlorophyll than maize shoots. The activities of RUBP carboxylase and phosphoenolpyruvate carboxylase were significantly greater in maize than in rice under Cd stress. Maize genotypes also possessed greater sucrose content and sucrose phosphate synthase activity in their shoots than rice genotypes. The oxidative damage as malondialdehyde and hydrogen peroxide was higher in rice genotypes. The rice genotypes showed greater induction of antioxidants such as superoxide dismutase, catalase, ascorbate peroxidase, glutathione reductase and ascorbic acid than maize genotypes. On the other hand, glutathione, proline, metallothioneins, total thiols content and glutathione-s-transferase activity were significantly higher in maize genotypes under Cd stress suggesting their superior capacity to deal with Cd toxicity. The observations indicated that the maize genotypes representing C4 plant type appear to have greater Cd tolerance than the rice genotypes representing C3 plant type. The findings speculate that C4 plant species may adapt to toxic metals such as Cd in a better way than C3 ones but further study involving several representatives of these plant types need to be carried out to corroborate it