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

First, second, and third leaves of barley (Hordeum vulgare L.cv. Atem) seedlings fumigated with 200 nl 1^–1 ozone for5 d were divided into equal length quarter sections before analysisof glutathione metabolism. Since the first leaf is the oldestand the third leaf is the youngest and since monocotyledonousleaves grow from the base, sections were of a widely differingage. Lipid peroxidation rose moderately in all sections in all leaves.However, severe damage, detected visibly as chlorosis and analyticallyas loss of soluble protein, occurred only in the oldest tissue. The specific activity of glutathione reductase was slightlyelevated in old and middle-aged tissue whilst the specific activityof glutathione-S-transferase rose markedly in old, middle-aged,and young tissue following fumigation. This may reflect theimportance of glutathione-S-transferase in the protection ofplant cells from oxidative stress products formed in membranes. Fumigation with ozone also caused a loss of total glutathionein the tip sections of all leaves. Explanations for these results, including age dependent proteinloss, are discussed. Key words: Barley, ozone, glutathione, developmental age, glutathione-S-transferase