Submitted to: Physiologia Plantarum
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2000
Publication Date: 10/1/2000
Citation: Burkey, K.O., Wei, C., Eason, G., Ghosh, P., Fenner, G.P. 2000. Antioxidant metabolites levels in ozone-sensitive and tolerant genotypes of snap beans. Physiologia Plantarum. 110(2):195-200 Interpretive Summary: Tropospheric ozone is a major air pollutant that has adverse effects on the growth and yield of agricultural crops. The development of ozone tolerant plants is one approach to alleviate this problem. Improvement of ozone tolerance requires knowledge of the critical points in plant metabolism that can be manipulated to provide greater protection against ozone stress without sacrificing yield or other desirable characteristics. Antioxidant compounds in leaf tissue have the potential to prevent or minimize ozone injury by neutralizing ozone and ozone-generated activated oxygen species. In this study, leaves from ozone-sensitive and ozone-tolerant snap bean genotypes were analyzed for ascorbic acid (vitamin C), glutathione and alpha-tocopherol (vitamin E) to determine if high levels of these antioxidant metabolites were associated with increased ozone tolerance. Leaf ascorbic acid was the only variable identified as a potential factor in ozone tolerance. Tolerant genotypes contained more ascorbic acid than sensitive lines, but the differences were not always statistically significant. Overall ozone sensitive and tolerant plants were not clearly distinguished by differences in leaf antioxidant content. The evidence suggested that screening for ozone tolerance based on antioxidant content is not a reliable approach.
Technical Abstract: Ozone-sensitive and tolerant genotypes of snap bean (Phaseolus vulgaris L.) were compared for differences in leaf ascorbic acid (vitamin C), glutathione and alpha-tocopherol (vitamin E) content to determine if antioxidant levels were related to ozone tolerance. Seven genotypes were grown in pots under field conditions during the months of June and July. Open top chambers were used to establish either a charcoal filtered (CF) air control (36 nmol mol-1 ozone) or a treatment where CF air was supplemented with ozone from 08:00 to 20:00 h with a daily 12 h mean of 77 nmol mol-1. Fully expanded leaves were analyzed for ascorbic acid, chlorophyll, glutathione, guaiacol peroxidase (EC 22.214.171.124) and alpha-tocopherol. Leaf ascorbic acid was the only variable identified as a potential factor in ozone tolerance. Tolerant genotypes contained more ascorbic acid than sensitive lines, but the differences were not always statistically significant. Genetic differences in glutathione and alpha- tocopherol were also observed, but no relationship with ozone tolerance was found. Guaiacol peroxidase activity and leaf alpha-tocopherol content increased in all genotypes following a one week ozone exposure, indicative of a general ozone stress response. Ozone had little effect on the other variables tested. Overall, ozone sensitive and tolerant plants were not clearly distinguished by differences in leaf antioxidant content. Screening for ozone tolerance based on antioxidant content is not a reliable approach.