Figure 1.

Diagrammatic representation showing the various sources of heavy metals and plant responses to heavy metal stress mediated toxicity. The initial stress response includes inhibition of seed germination and seedling growth. As part of initial defence plants utilize various morphological barriers and detoxification of heavy metals via metal ion binding and chelations. At the physiological and biochemical levels, the stress response is subsequetly reflected with decreased photosynthetic and respiration rates because of the changes in the ultrastructure of membrane in chloroplast and mitochondria, compromised pigment production, hormonal and nutrient imbalance, inhibition of DNA replication, gene expression and cell division, finally resulting in plant growth inhibition.