Time-course of Rubisco oxidation in beans (Phaseolus vulgaris L.) subjected to a long-term ozone stress

We investigated the time-course of Rubisco small subunit (Rubisco-SSU) oxidation in leaves of bean plants grown under elevated O-3. Five ambiences were tested in open-top chambers (OTCs): non-filtered air (NF), NF+20, +40, +60 and +80 ppb O-3. An unchambered atmosphere was also available. Four samplings were performed between 8 and 30 days after emergence. The dynamics of oxidation was studied with reference to leaf type (primary or trifoliate), leaf age and exposure duration. The oxidation was measured using an ELISA quantification of carbonyls present on amino acid side chains of Rubisco-SSU. Ozone was able to induce carbonyl derivative formation in both primary and trifoliate leaves. This oxidation process was always accompanied with visible foliar damage. As regards primary leaves, the oxidation varied with ozone dose and leaf age. A convenient ozone dose expressed as accumulated exposure over a threshold of 40 ppb (AOT40) is able to induce oxidation in mature leaves but not in very young leaves. Once near-full leaf span was reached, the carbonyl content had a good correlation with the ozone dose. In trifoliate leaves, ozone-induced oxidation of Rubisco-SSU was consistently lower and much less organized. Twenty-two days after emergence, a synthetic cumulative oxidation index computed per plant was linearly increased when plotted against AOT40. Finally, the time course of oxidation was discussed with special reference to the development pattern of leaf. (C) 2003 Elsevier Ireland Ltd. All rights reserved.