Heavy metal toxicity: Effect on plant growth and metal uptake by wheat, and on free living azotobacter

A pot study was conducted to investigate the toxic effects of certain heavy metals on the plant growth and grain yield of wheat (Triticum aestivum L.). The results revealed that heavy metals brought about significant reductions in both parameters, Cd being the most toxic metal followed by Cu, Ni, Zn, Pb and Cr. Moreover, the presence of Cd in the soil resulted in the maximum inhibition (84.9%) in the number of free living Azotobacter chroococcum cells over the control. The phytotoxicity was apparently due to the susceptibility of the free living Azotobacter chroococcum cells to the toxic doses of heavy metals. Protein content decreased from 19.0-71.4% in metal exposed plants at metal concentrations equivalent to those found in polluted soil. Metal uptake by grains was directly related to the applied heavy metal with greater concentrations of metals found in cases where metals were added separately rather than in combinations. The toxic effects on the plant growth, nitrogen content in plant parts, and protein content in grains, exerted by two metals in combination were not additive, but rather only as severe as for the most toxic metal alone.