VARIATION IN GLUTATHIONE AND ASCORBIC ACID CONTENT AMONG SELECTED CULTIVARS OF Phaseolus vulgaris PRIOR TO AND AFTER EXPOSURE TO OZONE

Measurements of reduced glutathione (GSH) and ascorbic acid (AA) concentrations in the primary leaves of four bean cultivars, two ozone-sensitive (S) and two ozone-insensitive (I), have revealed that GSH concentrations were not significantly different in all four cultivars prior to the exposure to ozone (0.28–0.32 ppm for 8 h); however, after ozone exposure GSH concentrations were significantly lower in the two sensitive cultivars, PHR and 0669, while in the two insensitive tolerants, FH and Nep-2, the drop in GSH concentrations was slight. The assay of glutathione reductase (GR), the enzyme which catalyzed the reduction of oxidized glutathione (GSSG) to its reduced form, namely GSH, indicated that its specific activity in the two insensitive cultivars was almost twice as high as in the two sensitive cultivars. The drop in AA concentration after 8 h of fumigation was moderate (although significant) in all four cultivars, whereas the concentrations of AA in all four cultivars prior to ozone fumigation were not significantly different. From the data it is suggested that differences in GR-specific activity, probably due to different isozymes, could be the reason for insensitivity or sensitivity to ozone among bean cultivars.Key words: Ozone, Phaseolus, glutathione, ascorbic acid, glutathione reductase