Heavy metal stress and crop productivity

Abstract

Heavy metal contamination of the environment through anthropogenic activities and/or natural processes is a widespread and serious problem. Heavy metals occur in various forms in soil, which differ greatly with respect to their solubility/ bioavailability. The geochemical behavior of heavy metals in soil, their uptake by plants, and effect on crop productivity is affected by various physicochemical properties of soil. Heavy metals mainly accumulate in root cells, due to their blockage by Casparian strips or due to trapping by the cell walls of roots. Excessive heavy metal accumulation in plant tissue impairs either directly or indirectly several biochemical, physiological, and morphological functions in plants and in turns interferes with crop productivity. Heavy metals reduce crop productivity by inducing deleterious effects to various physiological processes in plants including: seed germination, accumulation and remobilization of seed reserves during germination, plant growth, and photosynthesis. At the cellular level, heavy metal toxicity reduces crop productivity by producing reactive oxygen species, disturbing the redox balance and causing oxidative stress. Under heavy metal stress, plants have numerous defense mechanisms to manage heavy metal toxicity and to maintain their productivity, which include reduced heavy metal uptake by plants, sequestration into vacuoles, binding by phytochelatins, and activation of various antioxidants. This chapter presents the effect of heavy metals on physiological reactions in the plants’ crop productivity.