Review Article IJAAER (2016); 2(2): 125-132 Please cite this article as: Raja, S., A.A. Khan and M.N. Cheema. 2016. Plants tolerance mechanism and physiological effects under heavy metals stress. Int. J. Agric. Environ. Res., 2(2): 125-132. PLANTS TOLERANCE MECHANISM AND PHYSIOLOGICAL EFFECTS UNDER HEAVY METALS STRESS SHAMEEM RAJA A* , ASIF ALI KHAN A AND MASOOMA NASEER CHEEMA B a Department of Botany, Govt College Women, University, Faisalabad, Pakistan b Department of Plant Breeding and Genetics, University of Agriculture, Faisalabad, Pakistan Corresponding author E. mail: shameempbg@yahoo.com Abstract Escalating population is the potential cause for the increase in environmental pollution which ultimately affects human health as well as reduction in crops yield. One of the leading pollutants of human activity is the heavy metals. A number of essential i-e Cobalt (Co), Iron (Fe), Maganese (Mn), Molybdenum (Mo), Nickel (Ni), Zinc (Zn), Copper (Cu) as well as non-essential heavy metals i-e Lead (Pb), Cadmium (Cd), Chromium (Cr), Mercury (Hg) exist. Elevated concentration of heavy metals consequences in change of physiological processes such as inhibition of photosynthesis, enzyme activity, plant growth, lower uptake of water and nutrients due to inhibition of root growth etc. FAO have established secure limits of heavy metals for human and crops. Plants have developed tolerance mechanism against high concentration of heavy metals e.g. root exudates, binding with cell wall, expression of stress responsive genes and proteins, chelation of metals through organic acids and translocation into vacuoles or out of the cells. Different remediation techniques such as Farm yard manure (FYM), lime application, phytoremediation, soil dilution with clean soil, deep plugging, transgenic plants can be used as elucidation to this problem. Key Words: Heavy metals, effects, tolerance, remediation INTRODUCTION Different abiotic factors mainly drought, salinity, heavy metals, high and low temperature are responsible for crops yield reduction (Confalonieri, 2009). Heavy metals are important industrially and biologically, but are not degraded by any process (Sharmaa et al., 2007). Human activities lead to heavy metal pollution in soil and underground water. In future one of the alarming threats to crop productivity is the heavy metals stress (Wang et al., 2001, Jamali et al., 2007). Plants are responsible for transferring heavy metals from abiotic to biotic system (Horsfall et al., 2004; Mukesh, 2008). This review focus heavy metals effects on crops, plant response against heavy metals stress, tolerance mechanism and possible solutions related to plant heavy metals toxicity. A number of heavy metals exist, some of them are essential for plant growth at lower concentration (Cu, Zn, Mn, Ni, Fe, Mo, Co, ) (Salt et al., 1998; Parelta et al., 2000). These essential heavy metals are required for normal growth of plants and human beings e.g. in some enzymes, proteins (metallothionin) and cellular structures e.g. chloroplast (Babula et al., 2008; Kennedy and Gonsalves, 1989; Ren et al., 1993), so are essential for photosynthesis and metabolic activities etc. Some heavy metals ( V, Co, W, Cr , As, Hg, Ag, Sb, Cd, Pb, U ) are non-essential and cause toxicity to plant International Journal of Agricultural and Environmental Research FREE AND OPEN ACCESS Available online at www.ijaaer.com ISSN 2414-8245 (Online) ISSN 2518-6116 (Print)