Morphological, physiological and biochemical responses of plants to nickel stress: A review

Nickel (Ni), is the 22nd abundant element in the earth crust, being an essential mineral nutrient found in natural soils in trace concentrations. The elevated levels of Ni pollution in the environment are due to industrial and agricultural activities. It is vitally important to understand both, the functional characteristics and toxic effects of Ni in plants. The quantity of Ni required for normal growth and development of plants is very low. However, Ni has been identified as a component of various enzymes in plants and has decisive metabolism for certain enzyme activities, like maintaining proper cellular redox state and various other biochemical, physiological and growth responses. The higher concentration of Ni is associated with serpentine soils, manifestation in plant chlorosis and inhibits root and shoot growth. Excess of Ni inhibits a large number of enzymes and interferes with several aspects of plant biochemistry, including photosynthesis, pigment synthesis, and membrane integrity. This article is based on the overview of available data of past two decades that in core, itencompasses the ill morphological, physiological and biochemical effects of Ni stress on plants.   Key words: Nickel stress, growth, yield, antioxidative system, gas exchange, photosynthetic pigments.