Instrumental Approach to the Determination of Ozone Phytotoxicity

Abstract

Ozone (O3) phytotoxicity is a serious concern all over the globe. O3 can cause both biochemical and physiological changes to plants that could lead to reduction in growth and yield. Its effect on agricultural crops is usually detected as foliar injury. Although foliar injury has frequently served as physiological basis for monitoring performance of agricultural crops and assessing air quality, its visibility depends on period of exposure, concentration of ozone, and environmental conditions. The present study focused on the determination of biochemical indicators of ozone phytotoxicity including Rubisco (biochemical indicator for carbon assimilation), photo-pigments [carotenoids and chlorophyll (a & b)], and chlorophyll photochemical efficiency on a judiciously selected plant-Nicotiana tabacum (Tobacco), variety: Little Havanna. An enclosed computer controlled growth chamber was used for cultivation of the experimental plant groups (ozone exposed and control). Spectrophotometric measurements of the biochemical indicators were carried out to evaluate the exposure-response behaviour of the plant. Our results showed a significant (P< 0.05) decrease of the biochemical indicators that is reproducible even when foliar injury is not detected. Besides, experiments also showed that chlorophyll a is more sensitive to ozone than chlorophyll b. The instrumental readings were supported by a reduction in total organic nitrogen and starch content and ultimate decrease in growth rate and root: shoot ratio. While significant variations in the intensities of foliar injury can be detected among plants within a group, a reproducible exposure-response data were obtained from instrumental measurements. Such measurements can also serve as basis for the development of implantable sensors for in-situ monitoring of ozone pollution in sensitive crops.