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 High Carbon Dioxide Levels Cause Stress in Barley By Sharon DurhamJanuary 23, 2003 Atmospheric carbon dioxide levels have been rising steadily, and this elevated carbon dioxide can cause some plants to grow more rapidly. However, increased carbon dioxide can also have undesirable effects. For example, high carbon dioxide can worsen the adverse effects of high light intensity. Grass crops such as barley and wheat grown in high light will exhibit early aging and oxidative stress. Oxidative stress occurs when too much "active" oxygen accumulates in the plant, breaks down membranes and interferes with normal life processes such as photosynthesis. Exposure of wheat and barley seedlings to elevated carbon dioxide in high light levels for prolonged periods causes a breakdown of the chlorophyll that gives leaves their green color and is essential for photosynthesis. Thus, the leaves develop a bleached appearance. Agricultural Research Service plant physiologists J. Michael Robinson and Richard Sicher conducted studies that indicate the amount of key antioxidants such as vitamin C (ascorbic acid) significantly declines during the first two to three weeks of growth in barley primary leaves when exposed to high levels of carbon dioxide. Antioxidants help plants handle the accumulation of active oxygen, such as hydrogen peroxide and superoxide, which are byproducts of photosynthesis. Robinson and Sicher, with the Environmental Quality Laboratory and the Alternate Crops and Systems Laboratory in Beltsville, Md., think this decline in the ascorbic acid and other antioxidant levels may lead to symptoms of oxidative stress and plant aging. Lower antioxidant levels appear to be insufficient to handle strong oxidants or active oxygen types that are generated in high light levels. Breeders may use these findings in developing cultivars of wheat and barley with stronger antioxidant capacities for survival in high carbon dioxide atmosphere. ARS is the chief scientific research agency of the U.S. Department of Agriculture.


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