Physiological Effects of Cadmium on Plants: A review

Abstract

Heavy metals are important environmental pollutants and their toxicity is a problem of increasing significance for ecological, evolutionary, nutritional, and environmental reasons. Cadmium contaminated soil ecosystems pose serious threats on the morphological and physiological attributes of the plants. The exudation of secondary metabolites from roots is an effective mechanism adopted by plants to react and modify their environment. Extraction of cadmium and acclimatization in plants depends upon the potential of the plant species and their rhizospheric environment that enables to restrict cadmium entry roots through immobilization or promotes cadmium chelation with ionic species in rhizosphere that influence its solubilization and mobilization. Cadmium inhibits several physiological processes in plants, including seed germination and seedling growth, photosynthesis, antioxidation and affects plant growth and development. Cadmium toxicity in higher plants as well as in the soil - plant system has increased considerably; recently there are many gaps in our knowledge about the basic mechanisms that control cadmium movement and its accumulation in plants. Mechanism of Cadmium uptake by root, translocation, and its deposition within plants; needs more research; furthermore, forms of Cadmium in various staple plant foods need to be identified. We should elaborate to learning about the biochemistry of metal homeostasis factors, physical interaction of transporters, chelators and chaperones. A genetic approach as contrasting to physiological/ biochemical investigations may help understanding the mechanism of metal tolerance. Cadmium is perhaps the metal that has attracted the most attention in soil science and plant nutrition due to its potential toxicity to humans, and its relative mobility in the soil – plant system. Toxic symptoms of cadmium in plants such as, alterations in photosynthesis, stomatal regulation, enzymatic activities, water relation, mineral uptake, protein metabolism, membrane functioning. Summarizing, cadmium absorption and transport in plants, the effects of cadmium on plant growth and development, adaptation mechanisms of plants to cope with cadmium.