Simulating ozone detoxification in the leaf apoplast through the direct reaction with ascorbate

Abstract

This paper presents a mathematical model which enables the semi-quantification of ozone (O3) detoxification, based upon the direct reaction of the pollutant with ascorbate (ASC) located in the aqueous matrix associated with the cell wall (i.e. the apoplast). The model describes the uptake of ozone into the leaf and its direct reaction with ASC, taking into consideration the regeneration of dehydroascorbic acid in the cytosol, the rate of replenishment of cell wall ASC and the distribution of ASC between sub-cellular compartments based upon the permeability of biomembranes to the neutral species, ascorbic acid and the pH of various sub-cellular compartments. The importance of various physico-chemical characteristics (e.g. stomatal conductance, mesophyll cell wall thickness and tortuosity, chloroplast volume, apoplast pH, ASC:O3 reaction stoichiometry) in mediating the flux of ozone to the plasmalemma is analysed. Model simulations, supported by experimental observations, suggest that the ASC concentration in the leaf apoplast is high enough to scavenge a significant proportion of the O3 taken up into the leaf interior, under environmentally relevant conditions. However, there is considerable variation between taxa in the potential degree of protection afforded by apoplastic ASC, emphasizing the need for an improved understanding of the reaction chemistry of O3 in the cell wall.

A Novel Gene, OZONE-RESPONSIVE APOPLASTIC PROTEIN1, Enhances Cell Death in Ozone Stress in Rice

“…The induction of gene expression in ozone stress was significantly lower in the tolerant SL41 than in cv Nipponbare (Frei et al, 2010). From a physiological point of view, apoplastic ascorbate (AsA) has been shown to form the first line of defense against the ozone entering the plants through the stomata (Luwe et al, 1993;Plöchl et al, 2000;Feng et al, 2010), which supports the link between the annotation of the candidate gene and ozone stress tolerance. In line with this concept, a previous study demonstrated that an AO-overexpressing tobacco (Nicotiana tabacum) plant negatively affected tolerance to ozone due to altered apoplastic reduced AsA content and AsA redox status (Sanmartin et al, 2003).…”

Ozone exposure- and flux-based response relationships with photosynthesis, leaf morphology and biomass in two poplar clones

“…Species with low LMA are more reactive to environmental stimuli and also more sensitive to stress compared with species with high LMA, which are more stress tolerant (Bussotti, 2008). As leaves with lower LMA tend to have greater internal air spaces for diffusion to occur, more cell surface area is exposed to ozone and reactive oxygen species (ROS) internally, and most likely there is also a lower ability to produce anti-oxidants due to fewer cells and thinner cell walls (Plochl et al, 2000). In addition, a higher g s implies a higher flux of ozone to the intercellular space, and g s of clone 546 was higher than that of clone 107 under the same treatment and period.…”

Components of apoplastic ascorbate use in Betula pendula leaves exposed to CO2 and O3 enrichment

“…Rautenkrantz et al (1994) exposed purified barley protoplasts to various ASC concentrations and observed a saturation type uptake kinetics. From these data, Plöchl et al (2000) calculated a maximum uptake rate of 0.013 nmol m −2 plasmalemma s −1 . Foyer & Lelandais (1996) reported a maximum value of 0.34 nmol m −2 plasmalemma s −1 for isolated pea protoplasts.…”