ABSTRACT
Due to increasing mining activities, improper industrial effluent disposal and use of fossil fuels, heavy metal (HM) pollution has become a serious ecological issue. Metal accessibility is influenced by factors like soil pH, moisture and metal-ions concentration. Higher HM concentrations trigger symptoms including chlorosis, necrosis and ionic imbalance, which ultimately decline plant growth and productivity. Besides this, HM toxicity leads to imbalances in redox metabolism that cause oxidative harm by producing reactive oxygen species. The key steps to alleviate HM toxicity in plants are adsorption of HMs on the root surface, accumulation/compartmentalization in the vacuole and activation of antioxidative systems. Moreover, plant species synthesize organic compounds, such as sugars, amino acids, glycine betaine and polyamines, in response to HM stress to facilitate osmotolerance. Recently, genetic engineering to transform plants for metal uptake and sequestration has opened up new paths for improving plant proficiency against environmental stresses. Different genes participating in the biosynthesis of organic solutes have been identified from various sources. Transgenic plants with these ectopic/endogenous genes have been fruitfully used to synthesize compatible solutes which ultimately improve metal tolerance, thereby leading to agricultural sustainability. This chapter gives updated information about the effects of HM toxicity on plants and the role of organic solutes in stress alleviation.
