Age Dependent Damage and Glutathione Metabolism in Ozone Fumigated Barley: A Leaf Section Approach

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Abstract
First, second, and third leaves of barley (Hordeum vulgare L. cv. Atem) seedlings fumigated with 200 nl 1−1 ozone for 5 d were divided into equal length quarter sections before analysis of glutathione metabolism. Since the first leaf is the oldest and the third leaf is the youngest and since monocotyledonous leaves grow from the base, sections were of a widely differing age. Lipid peroxidation rose moderately in all sections in all leaves. However, severe damage, detected visibly as chlorosis and analytically as loss of soluble protein, occurred only in the oldest tissue. The specific activity of glutathione reductase was slightly elevated in old and middle-aged tissue whilst the specific activity of glutathione-S-transferase rose markedly in old, middle-aged, and young tissue following fumigation. This may reflect the importance of glutathione-S-transferase in the protection of plant cells from oxidative stress products formed in membranes. Fumigation with ozone also caused a loss of total glutathione in the tip sections of all leaves. Explanations for these results, including age dependent protein loss, are discussed.