Journal of the Kalash Science, Volume-2, Number-1, 2014 : 75-82 75 Plants defensive response against Cadmium toxicity stress: A review Prasann Kumar 1 , Neha Gogia 2 and Bhavika Tiwari 3 1 Department of Plant Physiology, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, 221005, India. 2 Genetic Engineering of Bacteria laboratory, Division of Bacteriology and Mycology, Indian Veterinary Research Institute, Izatnagar, 243122, India. 3 Department of Genetics and Plant breeding, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi, 221005, India. 1 Email : nehag0609@gmail.com Accepted: 13 April 2014 Abstract Cadmium (Cd), a heavy metal toxic to humans, animals and plants is a widespread pollutant with a long biological half-life. Cd is readily taken up by plant and leads to toxic symptoms. Cd damages the photosynthetic apparatus, lower chlorophyll, alters growth regulators contents followed by growth reduction. Plants exposed to cadmium are also more likely subjected to leaves pigment reduction. It has been found that the application of Polyamines (Put and Spd) on plant leaves not only maintains the leaf pigment but also enhances the rate of photosynthesis. Besides this, polyamines play a defensive role by being anti-oxidative agents and have often been seen accumulated in the plant organs in order to protect them against several stressful conditions. Salicylicate, SA is an endogenous growth regulator of phenolic in nature, which participates in the regulation of physiological processes in plants. These include effects on ion uptake, membrane permeability, etc. It in addition, interacts with other signaling pathways including those regulated by jasmonic acid and ethylene. The level of ABA in plants increases upon their exposure to environmental stress, such as drought, high temperature, low temperature, salinity and flooding. It appears that ABA is also a general endogenous inducer of tolerance to environmental stresses. Key words: Cadmium, Heavy metals, Polyamines, Toxicity. Introduction Cadmium (Cd) is a divalent heavy metal cation and is one of the most toxic heavy metals. It is supplied to soil, air and water mainly by effluent from industries, mining burning, leakage waste, by fertilization with phosphate and sewage sludge. Cd is readily taken up by plants, leading to toxic symptoms such as peroxidation of lipids, decreasing the glutamic acid, protein, potassium ion level and chlorophyll content, damaging cell’s photosynthetic machinery, inhibiting stomatal opening, increasing aspartic acid concentration and growth reduction. Abscisic acid (ABA), Nitric oxide (NO) and Reactive Oxygen Species (ROS) are mostly known for their response against a variety of stresses. However, polyamines (Put, Spm, Spd) have also been found to be linked both with ABA and NO. They initiate the production of nitric oxide, modulate stomatal closure (Alcazar et al. 2010) and are known for generation of Hydrogen Peroxide (H 2 O 2 ) during the catabolic reactions. Transgenic plants such as tobacco, Arabidopsis and sweet potato incorporated with SPDS gene have shown tolerance towards a variety of stresses. Besides the role of polyamines in plant several metabolic reactions, plant growth and development viz. organ development, fruit ripening, gene regulation, ageing and heavy metal toxicity (esp. Cd), they have also proved themselves to maintain the homeostatic environment in plant cells (Rodriguez Kessler et al. 2006). Due to their extensive applications or stress responses, they have been promoted from plant regulators to secondary messengers (Liu et al. 2007).