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Title: ANTIOXIDANTS IN SUN AND SHADE LEAVES OF SOUR ORANGE TREES (CITRUM AURANTIUM) AFTER LONG-TERM ACCLIMATION TO ELEVATED CO2

Author
item SCHWANZ, PETER - UNIVERSITAT FREIBURG, GM
item Kimball, Bruce
item Idso, Sherwood
item Hendrix, Donald
item POLLE, ANDREA - UNIVERSITAT FREIBURG, GM

Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: In order to determine the consequences of present and future global environmental changes on the security of world food production, efforts are underway to determine the growth and other physiological responses of major food crops to changing environmental factors. These global changes especially include the increasing concentration of atmospheric carbon dioxide (CO2) which is expected to double sometime during the next century. Climate modelers have predicted that the elevated CO2 will cause the earth to warm and that precipitation patterns will change. Elevated CO2 is also known to alter the growth of plants and may affect their production of antioxidants that protect the plants from ozone pollution and other oxidative stresses. Accordingly, measurements were made of concentrations of antioxidants in leaves from sour orange trees that have been grown in elevated CO2 concentrations for 7.5 years using open-top CO2 enrichment chambers. The results showed there were large differences in antioxidant levels between sun- and shade-adapted leaves and that elevated CO2 had little effect on the shade-adapted leaves. In contrast, high CO2 caused levels of one antioxidant, ascorbate, to increase in the sun-adapted leaves which suggests slightly increased tolerance of ozone or other oxidant pollution. Eventually, this wok should led to optimum management strategies and, of course, should ultimately benefit all future food consum

Technical Abstract: Antioxidant systems and the contents of pigments, malondialdehyde, soluble protein, and carbohydrate were investigated in sun- and shade- acclimated leaves of sour orange (Citrus aurantium) trees that had been grown for 7.5 years under ambient and elevated (+300 micro mol mol-1) atmospheric CO2 concentrations. Sun-acclimated leaves contained ginger ascorbate, glutathione, and soluble carbohydrate contents and had higher catalase activities than shade-acclimated leaves. Superoxide dismutase activities were similar in sun- and shade- acclimated leaves,and the activities of the two major isoforms decreased in response to enhanced CO2. In shade-acclimated leaves elevated CO2 caused increases in carbohydrate and ascorbate contents. There was no evidence for enhanced lipid perioxidation as assessed from the determination of the malondialdehyde contents under either conditions. The results are compatible with the concept that ascorbate, in addition to its function as an antioxidant, contributes to the regulation of photosynthetic electron flux, thereby preventing enhanced 02-production in leaves acclimated to high light conditions.