Apoplastic antioxidants as decisive elimination factors within the uptake process of nitrogen dioxide into leaf tissues

SUMMARY Uptake of NO2 via stomata and its elimination in the mesophyll are investigated by use of mathematical models. Systems of differential equations describe simultaneous diffusion and reaction of the chemical species taken into account. The common hypothesis, postulating the disproportionation reaction of NO2 being the predominant path for the transformation of NO2 into the cellular nitrate and nitrite pools, could be false because of its failure to reproduce the measured sorption characteristics. If however the reduction of the pro-oxidative NO2 by apoplastic ascorbate is taken into account the calculated uptake rates and the effects of changes in immission concentration and vegetational characteristics fit well within corresponding experimental results. The onset of acute injury in case of a fall in apoplastic ascorbate concentration below a critical level is postulated.