Tolerance of Plants to Air Pollutants

Abstract

Air pollutants cause various types of damage to plants: the retardation of growth, the promotion of ageing, the abscission of leaves and withering. Air pollutants are absorbed by plants mainly through the stomata of their leaves. The absorbed pollutants produce toxic substances in plants: SO2 produces SO₃^2-, NO₂ produces NO₂^- and all pollutants produce active oxygen species, such as O2-, H₂O₂ and ¹O₂, as secondary toxic substances to some extent. These substances destroy or inactivate various cellular components like proteins and lipids and cause damage to plants. On the other hand, plants have metabolic pathways to scavenge these toxic substances and can avoid damage when the amount of absorbed air pollutant is low.
The degree of damage to plants caused by air pollutants depends on the degree of stomatal opening and the potentials to produce and to scavenge toxic substances in plants. Plants also show dynamic responses to air pollutants: stomata tend to close when plants get contact with air pollutants and various activities to scavenge toxic substances in plants increase with the contact of plants with low concentrations of pollutants. The activities of active-oxygen-scavenging enzymes, superoxide dismutase and catalase, were shown to increase with SO₂ and activities of other such enzymes, ascorbate peroxidase and glutathione reductase increased with O₃. By contrast, the activity of nitrate reductase which produces toxic NO₂^- was shown to decrease with NO₂.
Genetic engineering technique is being used to change the tolerance of plants to air pollutants, based on these findings.