Biochemical defence mechanisms of plants to increased levels of ozone and other atmospheric pollutants

Some of the atmospheric gases at their supra optimum level become pollutant s and evoke various types of 'visible' and 'hidden' plant responses which u ltimately lead to reduced plant growth and productivity. The biochemical me chanism of the action of the pollutants is better understood now than it wa s about a decade ago. Participation of some of the signal molecules such as of H2O2 and salicylic acid is also known. It is believed that the generati on of oxy-free radicals is the principal biochemical event in responses of plants to any kind of environmental stress. Plants respond through increase d activities and levels of antioxidant enzymes and metabolites, so that the oxy-free radicals are removed and minimum damage is done. Attempts have be en made to modify the plant's responses to pollutant gases, through alterat ion in the levels of enzymes and metabolites involved in free radical scave nging. While earlier attempts were largely limited to agronomic practices o r in some cases to breeding programmes, attempts are now being made to prod uce transgenics and mutants with increased tolerance to the pollutants.