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Increasing food crisis in the present days has become a crucial point of concern throughout the world for mankind due to the pollution. Special occurrence of a molecule hegemonize its different characteristic and behavior thus the triatomic molecule ozone shields the life form on earth from UV-Ray while present in stratosphere but shows its deleterious effect for humans, plants and animal while present in troposphere. There is general scientific consensus that ground-level ozone (O3) levels have been rising markedly on large geographical scale and due to its phytotoxicity, it has been acknowledged as one of the most hazardous and noxious air pollutant with a higher degree of negative influence on global agriculture and trends predict that levels are projected to increase even more.
Ambient O3 levels affect plant life by obtaining foliar injury, altering primary and secondary metabolisms and hydraulic status, and promoting leaf senescence, which may decline the reproductive performances of essential crop plants. The economic loss for 23 horticultural and agricultural crops from O3 exposure was estimated to be approximately $6.7 billion for the year 2000 in Europe. Wang and Mauzerall (2004) anticipated economic losses of up to 9 % for four important cereal crops (viz., wheat, rice, maize and soybean) grown in China, South Korea and Japan.
Ozone is noxious to plants as it produces reactive oxygen species (ROS) after entering to the sub-stomatal cavity through stomata which play a fundamental role in determining the flux of O3 into the apoplastic region of the leaves causing a oxidative stress to the plant cell thus altering the plant cell ultrastructure and physiological as well as metabolical processes. Plants while exposed to ozone observed reduction in stomatal conductance but the internal mechanism is not that well understood although the presence of ozone is reported to alter the abscisic acid signaling or generate active oxygen species burst directly in guard cell. Extracellular H2O2 accumulation is one of the most remarkable responses which leads to develop visible foliar lesions as a consequence phosynthesis decline and NAD(P) dependent oxidase get activated resulting into more ROS accumulation. Most potent Reactive Oxygen Species the hydroxyl radicles act rapidly with proteins, lipids and DNA causing cell damage. The O3 readily damages the thylakoid membrane i.e. photosynthetic machinery leading to the loss in the activity of RuBisCO. Ozonolysis caused by ROS alter cellular functions, premature senescence and the regulation of specific genes.
Miller et al. observed premature senescence in 12 senescence-related genes of Arabidopsis thaliana (ecotype Lansberg erecta) induced by O3 thus altering many associated genes related early senescence. Ozone stress generates an array of enzymatic and non-enzymatic antioxidant molecules which help plant to combat against ROS. Magnitude of ozone response highly depends on the severity, frequency and longevity of exposure and sensitivity of that plant act against ozone.
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