@article{burkey_eason_fiscus_2003, title={Factors that affect leaf extracellular ascorbic acid content and redox status}, volume={117}, ISSN={["1399-3054"]}, DOI={10.1034/j.1399-3054.2003.1170106.x}, abstractNote={Leaf ascorbic acid content and redox status were compared in ozone‐tolerant (Provider) and ozone‐sensitive (S156) genotypes of snap bean (Phaseolus vulgaris L.). Plants were grown in pots for 24 days under charcoal‐filtered air (CF) conditions in open‐top field chambers and then maintained as CF controls (29 nmol mol−1 ozone) or exposed to elevated ozone (71 nmol mol−1 ozone). Following a 10‐day treatment, mature leaves of the same age were harvested early in the morning (06:00–08:00 h) or in the afternoon (13:00–15:00 h) for analysis of ascorbic acid (AA) and dehydroascorbic acid (DHA). Vacuum infiltration methods were used to separate leaf AA into apoplast and symplast fractions. The total ascorbate content [AA + DHA] of leaf tissue averaged 28% higher in Provider relative to S156, and Provider exhibited a greater capacity to maintain [AA + DHA] content under ozone stress. Apoplast [AA + DHA] content was 2‐fold higher in tolerant Provider (360 nmol g−1 FW maximum) relative to sensitive S156 (160 nmol g−1 FW maximum) regardless of sampling period or treatment, supporting the hypothesis that extracellular AA is a factor in ozone tolerance. Apoplast [AA + DHA] levels were significantly higher in the afternoon than early morning for both genotypes, evidence for short‐term regulation of extracellular ascorbate content. Total leaf ascorbate was primarily reduced with AA/[AA + DHA] ratios of 0.81–0.90. In contrast, apoplast AA/[AA + DHA] ratios were 0.01–0.60 and depended on genotype and ozone treatment. Provider exhibited a greater capacity to maintain extracellular AA/[AA + DHA] ratios under ozone stress, suggesting that ozone tolerance is associated with apoplast ascorbate redox status.}, number={1}, journal={PHYSIOLOGIA PLANTARUM}, author={Burkey, KO and Eason, G and Fiscus, EL}, year={2003}, month={Jan}, pages={51–57} }
 @article{heagle_miller_burkey_eason_pursley_2002, title={Growth and yield responses of snap bean to mixtures of carbon dioxide and ozone}, volume={31}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2002.2008}, abstractNote={ABSTRACTElevated CO2 concentrations expected in the 21st century can stimulate plant growth and yield, whereas tropospheric O3 suppresses plant growth and yield in many areas of the world. Recent experiments showed that elevated CO2 often protects plants from O3 stress, but this has not been tested for many important crop species including snap bean (Phaseolus vulgaris L.). The objective of this study was to determine if elevated CO2 protects snap bean from O3 stress. An O3–tolerant cultivar (Tenderette) and an O3–sensitive selection (S156) were exposed from shortly after emergence to maturity to mixtures of CO2 and O3 in open‐top field chambers. The two CO2 treatments were ambient and ambient with CO2 added for 24 h d−1 resulting in seasonal 12 h d−1 (0800–2000 h EST) mean concentrations of 366 and 697 μL L−1, respectively. The two O3 treatments were charcoal‐filtered air and nonfiltered air with O3 added for 12 h d−1 to achieve seasonal 12 h d−1 (0800–2000 h EST) mean concentrations of 23 and 72 nL L−1, respectively. Elevated CO2 significantly stimulated growth and pod weight of Tenderette and S156, whereas elevated O3 significantly suppressed growth and pod weight of S156 but not of Tenderette. The suppressive effect of elevated O3 on pod dry weight of S156 was approximately 75% at ambient CO2 and approximately 60% at elevated CO2 (harvests combined). This amount of protection from O3 stress afforded by elevated CO2 was much less than reported for other crop species. Extreme sensitivity to O3 may be the reason elevated CO2 failed to significantly protect S156 from O3 stress.}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Heagle, AS and Miller, JE and Burkey, KO and Eason, G and Pursley, WA}, year={2002}, pages={2008–2014} }
 @article{burkey_eason_2002, title={Ozone tolerance in snap bean is associated with elevated ascorbic acid in the leaf apoplast}, volume={114}, ISSN={["1399-3054"]}, DOI={10.1034/j.1399-3054.2002.1140308.x}, abstractNote={Ascorbic acid (AA) in the leaf apoplast has the potential to limit ozone injury by participating in reactions that detoxify ozone and reactive oxygen intermediates and thus prevent plasma membrane damage. Genotypes of snap bean (Phaseolus vulgaris L) were compared in controlled environments and in open‐top field chambers to assess the relationship between extracellular AA content and ozone tolerance. Vacuum infiltration methods were employed to separate leaf AA into extracellular and intracellular fractions. For plants grown in controlled environments at low ozone concentration (4 nmol mol−1 ozone), leaf apoplast AA was significantly higher in tolerant genotypes (300–400 nmol g−1 FW) compared with sensitive genotypes (approximately 50 nmol g−1 FW), evidence that ozone tolerance is associated with elevated extracellular AA. For the open top chamber study, plants were grown in pots under charcoal‐filtered air (CF) conditions and then either maintained under CF conditions (29 nmol mol−1 ozone) or exposed to elevated ozone (67 nmol mol−1 ozone). Following an 8‐day treatment period, leaf apoplast AA was in the range of 100–190 nmol g−1 FW for all genotypes, but no relationship was observed between apoplast AA content and ozone tolerance. The contrasting results in the two studies demonstrated a potential limitation in the interpretation of extracellular AA data. Apoplast AA levels presumably reflect the steady‐state condition between supply from the cytoplasm and utilization within the cell wall. The capacity to detoxify ozone in the extracellular space may be underestimated under elevated ozone conditions where the dynamics of AA supply and utilization are not adequately represented by a steady‐state measurement.}, number={3}, journal={PHYSIOLOGIA PLANTARUM}, author={Burkey, KO and Eason, G}, year={2002}, month={Mar}, pages={387–394} }
 @article{burkey_wei_eason_ghosh_fenner_2000, title={Antioxidant metabolite levels in ozone-sensitive and tolerant genotypes of snap bean}, volume={110}, ISSN={["0031-9317"]}, DOI={10.1034/j.1399-3054.2000.110208.x}, abstractNote={Ozone‐sensitive and tolerant genotypes of snap bean (Phaseolus vulgaris L.) were compared for differences in leaf ascorbic acid (vitamin C), glutathione and α‐tocopherol (vitamin E) content to determine whether 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 8:00 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 1.11.1.7) and α‐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 α‐tocopherol were also observed, but no relationship with ozone tolerance was found. Guaiacol peroxidase activity and leaf α‐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. The evidence suggests that screening for ozone tolerance based on antioxidant content is not a reliable approach.}, number={2}, journal={PHYSIOLOGIA PLANTARUM}, author={Burkey, KO and Wei, CM and Eason, G and Ghosh, P and Fenner, GP}, year={2000}, month={Oct}, pages={195–200} }
 @article{reinert_eason_2000, title={Genetic control of O-3 sensitivity in a cross between two cultivars of snap bean}, volume={125}, ISSN={["0003-1062"]}, DOI={10.21273/jashs.125.2.222}, abstractNote={Identification of genetic control of ozone (O3) sensitivity is desirable for selection of plant cultivars which are indicators of O3 stress. A cross was made between two cultivars of snap bean (Phaseolus vulgaris L.), `Oregon 91' (P1) and `Wade Bush' (P2), an O3-sensitive and O3-insensitive cultivar, respectively. Ten genetic populations (generations), `Oregon 91' (P1), `Wade Bush' (P2), F1, F2, backcrosses to both parents, and all reciprocal crosses, were field planted in each of two summers and evaluated for injury to O3. Ozone responses for the reciprocal crosses were not significantly different for any generation, so injury ratings from the reciprocal crosses were combined for each generation to provide six populations (P1, P2, F1, F2, BC1, and BC2) for analysis. When components of genetic variation were estimated from the six generations, additive genetic variance was the most important component in the total genetic variance available, although dominance variance was also a significant component. There was an inconsistency in the magnitude and the direction of the factors contributing to the dominance effects and also a large environmental component making up the phenotypic variance. Estimates of broad-sense heritability and narrow-sense heritability were 60% and 44%, respectively. Results suggest that O3-sensitive and O3-insensitive selections could be screened and evaluated in an ambient O3 environment. Several generations will be necessary, however, to develop `Bush Blue Lake' type selections that vary only in sensitivity to O3.}, number={2}, journal={JOURNAL OF THE AMERICAN SOCIETY FOR HORTICULTURAL SCIENCE}, author={Reinert, RA and Eason, G}, year={2000}, month={Mar}, pages={222–227} }
 @article{eason_reinert_simon_1996, title={Sulfur dioxide-enhanced phytotoxicity of ozone to watermelon}, volume={121}, number={4}, journal={Journal of the American Society for Horticultural Science}, author={Eason, G. and Reinert, R. A. and Simon, J. E.}, year={1996}, pages={716} }
 @article{eason_reinert_1991, title={Responses of closely related Bush Blue Lake snap bean cultivars to increasing concentrations of ozone}, volume={116}, number={3}, journal={Journal of the American Society for Horticultural Science}, author={Eason, G. and Reinert, R. A.}, year={1991}, pages={520} }