Plant Response towards Cadmium Toxicity: An Overview

Cadmium (Cd) is a naturally occurring element of relatively poor abundance (64 th amongst elements). It is one of the most common metal contaminant in ground water, soil and sediments due to its wide industrial application, hence posing a serious environmental concern. It exits in the soil solution primarily as Cd 2+ but also as Cd-chelates. Cadmium usually shares natural geologic association with Zn and Hg. Due to its strong mobility and high phytoavailability in soil, Cd is readily taken up by plant roots. Cd is taken up along with other essential elements such as Calcium and Zinc through transporters. Once inside the plant, it affects several cellular processes, plant growth and metabolic pathways. It interferes with nutritional uptake and impairs the process of photosynthesis, transpiration and respiration. Cd causes oxidative stress in plants either by blocking essential functional groups in bio-molecules or by altering the antioxidant defense system. It adversely affects the enzymatic machinery associated with sugar and nitrogen metabolism. Various Cd-hyperaccumulators have been explored and exploited in view of their phytoremediating properties. The present review summarizes an overview regarding the Cd availability in environment, Cd-induced toxic symptoms in plants, effect on germination, photosynthesis, biochemical and physiological alterations and Cd-hyperaccumulation.