Comparison of mercury, lead and arsenic with respect to genotoxic effects on plant systems and the development of genetic tolerance

• Published in: Environmental and Experimental Botany 2004-12, Vol.52 (3), p.199-223
• Main Authors: Patra, Manomita, Bhowmik, Niladri, Bandopadhyay, Bulbul, Sharma, Archana
• Format: Article
• Language: English
• Subjects: Adaptation to environment and cultivation conditions; adenosine diphosphate; adenosine triphosphate; Agronomy. Soil science and plant productions; air pollution; Arsenic; Biological and medical sciences; cell membranes; Fundamental and applied biological sciences. Psychology; genetic resistance; Genetics and breeding of economic plants; Genotoxicity; ion transport; Lead; literature reviews; Mercury; phosphates; phytotoxicity; plants; soil pollution; stress tolerance; sulfhydryl groups; Tolerance; uptake mechanisms; Varietal selection. Specialized plant breeding, plant breeding aims; water pollution
• ISSN: 0098-8472; 1873-7307
• DOI: 10.1016/j.envexpbot.2004.02.009

Metals can, when present in excess, or under wrong conditions, and in the wrong places, produce errors in the genetic information system. The present review is limited to three examples of heavy metal genotoxicants, namely arsenic (As), lead (Pb) and mercury (Hg) on plant systems. Exposure to lead is mainly through atmospheric pollutants, to mercury through soil and to arsenic through drinking water. Toxic metal ions enter cells by means of the same uptake processes as essential micronutrient metal ions. The amounts of metal absorbed by a plant depend on the concentrations and speciation of the metal in the soil solution, its movement successively from the bulk soils to the root surface, then into the root and finally into the shoot. Excessive concentrations of metals result in phytotoxicity through: (i) changes in the permeability of the cell membrane; (ii) reactions of sulphydryl (–SH) groups with cations; (iii) affinity for reacting with phosphate groups and active groups of ADP or ATP; and (iv) replacement of essential ions. Mercuric cations have a high affinity for sulphydryl groups and consequently can disturb almost any function where critical or non-protected proteins are involved. A mercury ion may bind to two sites of a protein molecule without deforming the chain, or it may bind two neighbouring chains together or a sufficiently high concentration of mercury may lead to protein precipitation. With organomercurials, the mercury atom still retains a free valency electron so that salts of such compounds form a monovalent ion. The effect of lead depends on the concentration, type of salts and plant species involved. Though effects are more pronounced at higher concentrations and durations, in some cases, lower concentrations might stimulate metabolic processes. The major processes affected are seed germination, seedling growth, photosynthesis, plant water status, mineral nutrition, and enzymatic activities. The phytotoxicity of arsenic is affected considerably by the chemical form in which it occurs in the soil and concentration of the metalloid. Due to its chemical similarity to phosphorus, arsenic participates in many cell reactions. Specific organo-arsenical compounds have been found in some organisms and arsenic has been reported to replace phosphorus in the phosphate groups of DNA. In view of the variety of reactions in plants that involve sulphydryl groups and phosphorus, arsenites and arsenates may interfere with physiological and biochemical