Ozone Concentration in Leaf Intercellular Air Spaces Is Close to Zero

Abstract

Transpiration and ozone uptake rates were measured simultaneously in sunflower leaves at different stomatal openings and various ozone concentrations. Ozone uptake rates were proportional to the ozone concentration up to 1500 nanoliters per liter. The leaf gas phase diffusion resistance (stomatal plus boundary layer) to water vapor was calculated and converted to the resistance to ozone multiplying it by the theoretical ratio of diffusion coefficients for water vapor and ozone in air (1.67). The ozone concentration in intercellular air spaces calculated from the ozone uptake rate and diffusion resistance to ozone scattered around zero. The ozone concentration in intercellular air spaces was measured directly by supplying ozone to the leaf from one side and measuring the equilibrium concentration above the other side, and it was found to be zero. The total leaf resistance to ozone was proportional to the gas phase resistance to water vapor with a coefficient of 1.68. It is concluded that ozone enters the leaf by diffusion through the stomata, and is rapidly decomposed in cell walls and plasmalemma. diffusion resistance of the whole gaseous pathway from cell surfaces to ambient air:where E2 is the transpiration rate (minus cuticular transpiration); rg, the diffusion resistance in the leaf gaseous phase to water vapor; wi, the water vapor concentration at evaporating cell surfaces; and wa, that in the ambient air. CO2 is a heavier gas (M = 44) than water vapor (M = 18); therefore, CO2 moves more slowly than water vapor through the same diffusion pathway and at the same concentration difference. The ratio of the diffusion coefficients of H20 and CO2 in the leaf gaseous pathway was measured to be 1.62 (9).We could not find a value of the diffusion constant for 03 in air, DZ, in the literature. However, diffusion constants for various gas mixtures may be calculated using the molecular parameters of component gases (1) 0.43 X (T)00) X Abbreviations: E, transpiration rate; wa, wi, water vapor concentration in ambient air (a) and on evaporating cell surfaces (i); r8, rg, leaf gas phase diffusion resistance to water vapor (w) and to ozone (z); M, molecular weight; DW, Dz, diffusion constant for water vapor (w) and for ozone (z); T, temperature, Tk, critical temperature; Vk, critical volume; P, atmospheric pressure; Za, zi, ozone concentration in ambient air (a) and in the leaf intercellular air space (i); Q, ozone uptake rate; v, gas flow rate; S, leaf area; gz, total leaf conductance for ozone; rz, total leaf resistance to ozone; gge ggz, leaf gas phase diffusion conductance for water vapor (w) and for ozone (z).

Determinants of stomatal sluggishness in ozone-exposed deciduous tree species

“…This method assumes the O 3 concentration inside leaves to be close to zero (Laisk et al, 1989;Omasa et al, 2002). Stomatal conductance to O 3 can be then derived from g s and ambient O 3 concentrations multiplied by 0.613, i.e., the ratio of diffusivities between O 3 and water vapor (Wieser et al, 2002).…”

Concentration- and flux-based ozone dose–response relationships for five poplar clones grown in North China

“…It is empirically assumed that the O 3 concentration inside the intracellular spaces of the leaf was approximately zero (Laisk et al, 1989). Hence, Eq.…”

Impacts of ozone on Plantago major: apoplastic and symplastic antioxidant status

“…Once inside the leaf, the aqueous phase of the cell wall (the apoplast) constitutes a near-perfect sink for the pollutant (Laisk et al, 1989). There is evidence that various reactive oxygen species (ROS) are formed following the reaction of O $ with constituents of the apoplast implying that these ROS govern the phytotoxicity of the pollutant (Grimes et al, 1983 ;Mehlhorn et al, 1990 ;Kanofsky & Sima, 1991, 1995Runeckles & Vaartnou, 1997).…”