Air Pollutants and Photosynthetic Efficiency of Plants
Absorption and accumulation/integration of air pollutants by leaves induce physiological and biochemical alterations in plants. Photosynthesis is the basic physiological event affected in plants exposed to air pollutants. Reduction in leaf area, closure o
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Air Pollutants and Photosynthetic Efficiency of Plants Bhupinder Dhir
Abstract
Absorption and accumulation/integration of air pollutants by leaves induce physiological and biochemical alterations in plants. Photosynthesis is the basic physiological event affected in plants exposed to air pollutants. Reduction in leaf area, closure of stomata and the damage to the photosynthetic apparatus limit the photosynthetic capacity of plants. High concentrations of sulphur dioxide (SO2), ozone (O3) and nitrogen oxides (NOx) induce stomatal closure limiting the availability of carbon dioxide (CO2) for photosynthesis. Reactive oxygen species (ROS) generated during oxidative stress damage photosynthetic apparatus via alteration in thylakoid structure and function. The photosynthetic electron transport, carboxylation efficiency of RuBisco and chlorophyll biosynthesis are the major processes negatively affecting the photosynthetic efficiency of plants. Keywords
Photosynthesis • Leaf area • Thylakoid structure • Stomatal closure • Reactive oxygen species • Chlorophyll
7.1
Introduction
The combustion of fuels, automobile emissions and industrial operations release toxic gases such as sulphur dioxide (SO2), nitrogen oxides (NOx), carbon dioxide (CO2), carbon monoxide (CO), hydrogen fluoride (HF) and particulates (PM) in
B. Dhir (*) Department of Genetics, University of Delhi South Campus, New Delhi 110021, India e-mail: [email protected]
the atmosphere (Agbaire and Esiefarienrhe 2009). Primary pollutants undergo further reactions such as photolysis to produce secondary pollutants viz. peroxyacetyl nitrate (PAN) in the atmosphere (Agbaire 2009). The presence of polycyclic aromatic hydrocarbons (PAHs) and heavy metals makes the particulate matter (PM) (size ≥100 μm) toxic (Jouraeva et al. 2002; WHO 2006; Yu et al. 2006; Uzu et al. 2010). The increase in the emission of most of the pollutants noted in the last few years with an annual increment of 0.5–2 % has adversely affected the living
© Springer Science+Business Media Singapore 2016 U. Kulshrestha, P. Saxena (eds.), Plant Responses to Air Pollution, DOI 10.1007/978-981-10-1201-3_7
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B. Dhir
72 Alteration in enzyme activity acidic pH
SO2
(HSO3-, H2SO4, HNO3)
NO2
O3
Changes in the metabolic events (photosynthesis)
H2O
ROS production
oxidative stress
reduced leaf area
damage to membranes
reduced chlorophyll
Photosynthetic inhibition
decline in photosynthesis
Fig. 7.1 Modes of action of various pollutants in reducing photosynthesis
organisms all over the world (Ashmore 2005). Predictions suggest the increase in the emission rate by 40–60 % by 2100 (IPPC 2007). The concentrations of gaseous pollutants are much higher in urban air in developing and developed countries (Li 2003; Tiwari et al. 2006). Among all the pollutants, carbon dioxide (CO2) emissions have seen a drastic increase over the decades and are expected to exceed 700 μmol mol−1 by the end of the twenty-first century (IPCC 1997). Exposure to high concentrations of gaseous pollutants such as NO2, SO2,
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