Chapter 8 - Effect of heavy metals on growth, physiological and biochemical responses of plants

Abstract

Plants being sessile confronts a variety of biotic and abiotic environmental adversities. Heavy metals (HMs) stress is a significant abiotic constraint to agricultural production around the world. Sources of HMs in environment include natural as well as anthropogenic activities such as sewage sludge, municipal and industrial waste, phosphate fertilizers, and mining activities. Aluminum, cadmium, copper, chromium, mercury, manganese, lead, and zinc are among the major toxic heavy metals. Additionally, some metalloids namely arsenic and antimony are also considered as toxic. Albeit, some HMs are essential micronutrients and are involved in many metabolic processes in plants. However, their excess can cause detrimental effects on plant growth, metabolism, and yield. Heavy metals cause deterioration of chlorophyll pigments, chloroplast ultrastructure, and disorganization of mitochondria. Heavy metals adversely impact physiology and morphology of seeds obstructing germination process and early seedling growth in plants. Excess HM also cause disturbance in plant water relations. Heavy metals impair essential physiological processes entailing photosynthesis, water relations, and chlorophyll fluorescence. Heavy metals compete with other essential nutrients and hinder their uptake in plants, thereby limiting crop growth and yield. Heavy metals stress cause excessive production of reactive oxygen species (ROS), which impair key cellular components such as nucleic acid, proteins, cellular membranes in plants. Consequently, it results in the higher accumulation of oxidative stress indicator such as malondialdehyde as well as increased activities of ROS detoxifying enzymes.