The relationship between ozone insensitivity, lipid-soluble antioxidants, and superoxide dismutase in Phaseolus vulgaris

Ozone insensitivity was assessed by three methods (visual rating, leakage of amino acids, and leakage of total electrolytes from leaf discs), and related to the levels of lipid-soluble antioxidants and superoxide dismutase activity in the primary leaves of different ages and of different cultivars of Phaseolus vulgaris L. The most sensitive indicator of ozone injury was visual rating. The increased variability associated with measurements of amino acid or total electrolyte leakage masked differences among cultivars which could be detected by visual rating. The correlations among the three measures of injury were high. Ozone tolerance of the primary leaf decreased between 8 and 18 days after planting and varied significantly among the 10 cultivars tested. Similarly, significant differences in lipid-soluble antioxidant content and superoxide dismutase activity were measured, but a correlation with ozone insensitivity was not established. Exposure to 20 pphm ozone for 24 h induced higher quantities of lipid-soluble antioxidant in the susceptible cv. Seafarer but not in the tolerant cv. Goldcrop. Superoxide dismutase increased similarly in both cultivars. The physiological mechanism of ozone insensitivity in the primary leaves of these cultivars of P. vulgaris was not shown to involve increased levels of lipid-soluble antioxidants or superoxide dismutase.