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Factors that affect leaf extracellular ascorbic acid content and redox status

Authors

  • Kent O. Burkey,

    1. United States Department of Agriculture-Agriculture Research Service, Box 7631, North Carolina State University, Raleigh, North Carolina 27695-7631, USA
    2. Department of Crop Science, North Carolina State University
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  • Gwendolyn Eason,

    1. Department of Plant Pathology, North Carolina State University
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  • Edwin L. Fiscus

    1. United States Department of Agriculture-Agriculture Research Service, Box 7631, North Carolina State University, Raleigh, North Carolina 27695-7631, USA
    2. Department of Crop Science, North Carolina State University
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*Corresponding author, e-mail: koburkey@unity.ncsu.edu

Abstract

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.

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