Lead (Pb)-induced biochemical and ultrastructural changes in wheat (Triticum aestivum) roots

The focus of the present study was to explore lead (Pb)-induced metabolic alterations vis-A -vis ultrastructural changes in wheat roots to establish Pb toxicity syndrome at a structural level. Pb (50-500 mu M) enhanced malondialdehyde (an indicator of lipid peroxidation) and hydrogen peroxide content, and electrolyte leakage, thereby suggesting reactive oxygen species-induced disruption of membrane integrity and oxidative stress in wheat roots. The activities of superoxide dismutases and catalases enhanced upon Pb exposure, whereas those of ascorbate and guaiacol peroxidases declined. Pb-induced metabolic disruption was manifested in significant alterations in wheat root ultrastructure as analyzed by transmission electron microscopy. Pb caused thinning of cell wall (at 50 mu M), formation of amoeboid protrusions and folds and intercellular spaces, and appearance of lesions and nicks/breaks (at a parts per thousand yen250 mu M Pb). Pb was deposited along the cell walls as dark precipitates. At a parts per thousand currency sign250 mu M Pb, the number of mitochondria increased significantly, whereas structural damage in terms of change of shape and disintegration was observed at a parts per thousand yen 250 mu M Pb. Pb reduced the size of nucleoli and induced puff formation (at 250 mu M), resulting in complete disintegration/disappearance of nucleolus at 500 mu M. The study concludes that Pb inhibited wheat root growth involving an ROS-mediated oxidative damage vis-A -vis the ultrastructural alterations in cell membrane and disruption of mitochondrial and nuclear integrity.