**3.4 Heavy metal toxicity**

Heavy metals adversely affect plant's physiological, morphological, biochemical and molecular activities. After root uptake, heavy metals *viz*., Pb, Cu, Hg, etc. translocate inside the plant through xylem in response of transpiration pool and affect nutrient distribution, photosynthesis, enzyme activities, Cu/ Zn-SOD, ethylene receptors etc. and consequently, decrease molecular oxygen and synthesize reactive oxygen species (ROS) (oxidative stress) [22]. Formation of ROS damages the cell further.
