Diffusions/Reaktionsmodell Für S02 Am Blattpfad

The concentration of S(IV) in leaf cells is determined by a steady-state equilibrium. The input term is given by diffusion of SO2, solution of SO2 in cell wall liquids and the dissociation-equilibrium of [SO2·H2O] [S03 2-] [HSO3 -]. The output term describes the metabolisation (elimination) of S(IV). Under physiological conditions and with open stomata (i.e. resistance « 104sec·m-1) the velocity of elimination is neglegible compared with the velocity of the input. In this case the S(IV)-concentration in leaf cells is determined almost exclusively by the input term. Under these circumstances the S(IV) concentration inside the cell (c5) is about 105 times the S02 concentration in the environment (c1). For the same reason changes in vmax of the elimination reaction over a range of 102 (0.000054–0.0054) don’t change the S(IV) level significantly (differences < 0.1%). Only during the night when the stomata are closed (resistance: 1.3x104 sec·m-1) the input velocity decreases sufficiently to show a visible effect of elimination reactions on the steady-state equilibrium.