CHANGES IN THYLAKOID PROTEIN-PATTERNS AND ANTIOXIDANT LEVELS IN 2 WHEAT CULTIVARS WITH DIFFERENT SENSITIVITY TO SULFUR-DIOXIDE

Plants of two wheat cultivars (Triticum aestivum L., cultivars 'Mec' a nd 'Chiarano'), each with a different sensitivity to sulfur dioxide (S O2), were exposed continuously to 2, 23, 64 and 96 nl l(-1) SO2 for 4 months. To investigate whether the higher resistance to SO2 of Chiaran o was due to increased activities of detoxification systems, some anti oxidant enzymatic and non-enzymatic systems were analyzed. Moreover, t o test whether the different responses of the two cultivars to SO2 wer e related to different changes at thylakoid level, we analyzed the thy lakoid polypeptide patterns by two-dimensional electrophoresis. Two-di mensional gels of thylakoid membranes revealed a more pronounced gener alized decrease of spot optical density in the more SO2-sensitive Mec; following SO2 fumigation, changes were observed in the area with mole cular masses 26-29 kDa and isoelectric point (pI) 5-6 and molecular ma sses 24-27 kDa and pI 5.7-5.8. A significant decrease in optical densi ty of a spot with a molecular mass of 32 kDa and pI 5.4, reported to b e D1 protein of the photosystem II reaction centre, was observed in th e leaves of both cultivars fumigated with 96 nl l(-1) SO2. Catalase ac tivity was unaffected by SO2 exposure. Following SO2 fumigation, super oxide dismutase activity decreased in Chiarano, but remained unchanged in Mec. Both cultivars were found to increase guaiacol and ascorbic p eroxidase activities as a response to SO2. The redox status of ascorbi c acid was similar in both cultivars and was unaffected by SO2. Howeve r, the content of ascorbic acid was higher in the more tolerant Chiara no than in Mec at all SO2 concentrations. The data reported here confi rmed the different sensitivities to SO2 of the two cultivars, as demon strated by thylakoid protein analysis, and suggest that this differenc e depends on a differential ability to maintain elevated levels of asc orbic acid rather than on increasing detoxifying enzyme activities. (C ) 1997 Elsevier Science B.V.