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Plasmalemma protection by the apoplast as assessed from above-zero ozone concentrations in leaf intercellular air spaces

Moldau, Heino, Bichele, Irina
Planta 2002 v.214 no.3 pp. 484-487
apoplast, ozone, Phaseolus vulgaris, air, plasma membrane, stomata
To evaluate reactive absorption of ozone (O₃) in the leaf apoplast, amphistomatous leaves of Phaseolus vulgaris L. were allowed to take up O₃through the stomata on the lower leaf surface at high rates for 3–5 min. Up to 5% of the O₃taken up diffused through the leaf and emerged from the stomata on the upper surface, suggesting above-zero O₃concentrations in the leaf intercellular air space, [O₃]ᵢ. Moreover, measurements revealed that [O₃]ᵢincreased during exposure to the pollutant. Time patterns of O₃fluxes through the gas phase and into the aqueous apoplast indicated that the increase in [O₃]ᵢwas the result of a decrease in the diffusion-reaction conductance of the aqueous apoplast, gₐq. Under an intense O₃pulse, gₐqapproached the value of the pure diffusional conductance within 2.5 min of exposure, suggesting the exhaustion of protective resources in the leaf apoplast. Toward the end of the exposure gₐqtended to increase, suggesting either a recovery in the protective resources in the leaf apoplast and/or the induction of new defences. The possibility of estimating the degree of protection afforded by apoplast constituents and the rate of recovery of these protective systems in intact leaves using brief O₃pulses is discussed.