Factors that affect leaf extracellular ascorbic acid content and redox status

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.

Assessing the effects of ambient ozone in China on snap bean genotypes by using ethylenediurea (EDU)

“…AsA is a key metabolite in antioxidant system that protects plant from ROS, acting as a chemical scavenger and/or as a substrate of extracellular enzymes such as the ascorbate peroxidase (APX), therefore affecting propagation of initial ozone signal (Burkey et al, 2006;Dizengremel et al, 2013;Feng et al, 2010b). Differences in AsA content have been related to differences in ozone sensitivity (Burkey et al, 2003;Feng et al, 2010b). In our study, higher total AsA in NX816 could partly explain the higher ozone tolerance of this genotype, but no significant responses to EDU were observed.…”

Targets for Crop Biotechnology in a Future High-CO2 and High-O3 World

“…Ascorbate is one of the major antioxidants thought to govern O 3 tolerance in plants, and total ascorbate content has been correlated with O 3 tolerance in a wide range of species (for review, see Conklin and Barth, 2004). Localization of ascorbate or other antioxidants to the apoplastic space, where interception and detoxification occurs, appears to be important in protection from O 3 damage, as is recycling of ascorbate back to the reduced ''anti-oxidant'' state (Burkey et al, 2003;Conklin and Barth, 2004 Components of the O 3 sensing and signaling pathways seem to be good potential targets for biotechnological manipulation to improve crop productivity. For instance, ethylene-insensitive mutants of Arabidopsis (Arabidopsis thaliana) and birch (Betula spp.)…”

Diurnal variation of apoplastic ascorbate in winter wheat leaves in relation to ozone detoxification

“…The apoplastic ascorbate accounts for up to 5% of the whole leaf ascorbate pools (Noctor and Foyer, 1998) and appeared to be sufficient to detoxify a significant portion of O 3 under environmentally relevant conditions (Chameides, 1989;Lyons et al, 1999;Plochl et al, 2000;Frei et al, 2010). Also, most evidence has shown a close positive correlation between O 3 tolerance and apoplastic ascorbate contents in different plants (Burkey et al, 2003(Burkey et al, , 2006Feng et al, 2010;Frei et al, 2010;Zheng et al, 2000) with an exception in Trifolium repens (D'Haese et al, 2005). Therefore, the ascorbate especially in the apoplast has been used to represent the capacity of O 3 detoxification (Heath, 2008).…”