Cadmium stress in plants: A critical review of the effects, mechanisms, and tolerance strategies

Cadmium accumulation in crops and the possibility of Cd entering the food chain are serious concerns for public health. This review discusses the deleterious effects of Cd in plants and the tolerance and resistance mechanisms that evolved to help mitigate cadmium toxicity. Cadmium reduces seed germination, early seedling growth, and plant biomass. It causes changes in photosynthesis, relative water content, transpiration rate, stomatal conductance, and electrolyte leakage. Cadmium activates the reactive oxygen species that induce chromosomal aberrations, gene mutations, and DNA damage that affect the cell cycle and cell division. In response, plants have applied several adaptive strategies to overcome and reduce the toxic effects of Cd. The primary detoxification mechanisms are exclusion and accumulation of Cd in specific plant parts. Plants also adapt to Cd toxicity with the help of signaling pathways that regulate survival and growth under Cd stress. Other mechanisms such as synthesis of plants hormones, activation of the antioxidant system and the production of phytochelatins and proline are extremely helpful in plant tolerance to Cd. Furthermore, soil microorganisms play a crucial role toward the Cd tolerance in plants by decreasing metal phytoavailability and increasing morphological and physiological parameters of plant.