ABSTRACT
Heavy metals (HMs) are naturally present in the terrestrial and aquatic environments. Heavy metal toxicity is one of the major abiotic stresses in plants. The level of heavy metal toxicity depends on several factors including the dose, route of exposure and chemical state. A HM is not toxic per se, it is only toxic when its concentration in the plant exceeds a certain threshold. Though copper is an essential metal for normal plant growth and development, it is also potentially toxic at supra-optimal concentration. The negative influence of heavy metals on the growth and activities of soil microorganisms also indirectly affects the growth of plants. After sensing the HM, the plant cell activates specific genes to neutralize the stress stimuli. Even gene expression patterns may change in response to toxic elements. Some heavy metals play an important role in plants cells as micronutrients, while others have stimulating and provoking effects on plants even in trace concentrations.
