Phenolics: Accumulation and Role in Plants Grown Under Heavy Metal Stress

Abstract

Heavy metals such as Fe, Mn, Cu, Ni, Co, Cd, Zn, Hg and As have long been gathering in soils as a result of variety of anthropogenic activities particularly after the setup of industrial sector. Plants exposed to high levels of these heavy metals undergo number of changes in their physiology and metabolism. The most typical and visible manifestation of heavy metal toxicity includes reduced plant growth, leaf chlorosis, leaf necrosis, turgor loss, instant drop in seed germination rate and a defunct photosynthetic apparatus, which is frequently associated with progressive senescence processes or ensuing plant death. In plants, heavy metal stress also increases the generation of free radicals and many other detrimental species. To defend themselves against heavy metal stress, plants employ a various avoidant or tolerant mechanisms. One such mechanism that provides plants with a defensive strategy to deal with severe heavy metal toxicity is the synthesis of phenolics, which are secondary natural metabolites originating biogenetically from either the shikimate/phenylpropanoid pathway or acetate/malonate pathway. The present review lays focus on the structure, synthesis, accumulation and role of phenolics in ameliorating the detrimental effects of heavy metals in plants.