Comparison of effects of air pollutants (SO2, O 3, NO 2) on intact leaves by measurements of chlorophyll fluorescence and P700 absorbance changes.

The immediate effects of short exposures to high concentrations of different air pollutants (20 min SO2, 2 h O3, and 4 h NO2, 5 ppm each) on chlorophyll fluorescence and P700 absorbance changes at 830 nm of intact spinach leaves were investigated. Three different types of fluorescence measurements were used: Fluorescence rise kinetics in saturating light, fast fluorescence induction kinetics (Kautsky-effect), and slow induction kinetics with repetitive application of saturation pulses (saturation pulse method).The results show that the various air pollutants caused rather different damage in the photosynthetic apparatus of the leaves: 1. SO 2: The main effect is due to the acidifying action, weakening the PS II donor side (suppression of I1-I2-P phase in fluorescence) and inhibiting Calvin cycle activation (no relaxation of membrane energization). 2. O 3: Ozone has apparently no specific point of attack due to its high reactivity. It obviously reacts with all cell membranes, but primarily with the plasma membrane which it first passes on the way into the leaf. 3. NO 2: NO2 produces HNO3 and HNO2, when dissolved in the leaf water. The nitrite reductase, however, is highly effective, so that (in the light) nearly all nitrite is reduced. By the reduction of nitrite to ammonia, OH(-) is produced preventing net acidification. Obviously, the electron transport rates, which are possible with nitrite as acceptor are very high, being comparable to those observed with the well-known Hill reagent methylviologen, as revealed by P700 measurements in saturating light. Such high reactivities with NO2 (-) must prevent assimilatory electron flow.