ABSTRACT
Photosynthesis is a physico-biochemical process that traps the solar energy and carbon from the atmosphere and reduces it to fulfill the energy needs of most of the organisms existing on earth. This process may be regarded as the main driving force to evolve various forms of life on earth. But this vital process is greatly affected by the increased concentration of heavy metals in the environment. Although, heavy metals such as Cu, Zn, Mn, Fe, Mo, Ni, and Co, serve as micronutrient for various physiological and growth promoting activities such as photosynthesis, protein synthesis, fat metabolism and acts as cofactors in many enzyme activities. Heavy metal exposure in increased concentration greatly influenced the photosynthetic process either directly or indirectly. Various experimental studies revealed the adverse effect of heavy metal on anatomical features of the plants involved in photosynthesis such as deformed chloroplast, poorly developed leaves, and abnormal stomata structure. Heavy metals also impose an adverse effect on the biochemistry of photosynthesis such as photosystem I (PSI) and photosystem II (PSII). Photosystem II, an oxygen evolving process of photosynthesis, is responsible for the maintenance of aerobic life on earth. It is noticeable that PSII is more sensitive to heavy metal in comparison to PSI. Most of the heavy metal studies revealed that the oxygen evolving system that plays a crucial role in generating electrons and hydrogen ions to maintain electrochemical gradient for generation of assimilatory power becomes the target site for the binding of various heavy metals. Heavy metals interfere with various enzymatic activities 150involved in dark phase synthetic process of photosynthesis such as ALA synthase (precursor of tetrapyrrole), RuBPcase and PEP-carboxylase. Heavy metal ions alter the functioning of photosynthetic enzymes by interacting with the SH groups.
