APOPLASTIC ANTIOXIDANTS AS DECISIVE ELIMINATION FACTORS WITHIN THE UPTAKE PROCESS OF NITROGEN-DIOXIDE INTO LEAF TISSUES

Uptake of NO2 via stomata and its elimination in the mesophyll are inv estigated by use of mathematical models. Systems of differential equat ions describe simultaneous diffusion and reaction of the chemical spec ies taken into account. The common hypothesis, postulating the disprop ortionation reaction of NO2 being the predominant path for the transfo rmation of NO2 into the cellular nitrate and nitrite pools, could be f alse because of its failure to reproduce the measured sorption charact eristics. If however the reduction of the pro-oxidative NO2 by apoplas tic ascorbate is taken into account the calculated uptake rates and th e effects of changes in immission concentration and vegetational chara cteristics fit well within corresponding experimental results. The ons et of acute injury in case of a fall in apoplastic ascorbate concentra tion below a critical level is postulated.