Light-induced changes in the quenching of 9-amino-acridine fluorescence by photosynthetic membranes due to atmospheric pollutants and their products

Abstract

The normal changes in light-induced quenching of 9-amino-acridine fluorescence by detached thylakoid membranes obtained from lysed oat chloroplasts were compared with those in the presence of various concentrations of added ozone, sulphite, sulphate, nitrite and/or nitrate in order to determine if the ability of the photosynthetic membranes to create and maintain effective proton gradients were affected by the likely products of atmospheric pollution within plastids. No disturbances of thylakoid properties due to sulphate occurred below 2 m m whilst only concentrations of nitrate, sulphite or nitrite greater than 1 m m appeared to significantly affect the redistribution of the 9-amino-acridine probe in the light. Pulses of ozone, by contrast, were highly effective in creating significant reductions in light-induced quenching of 9-amino-acridine fluorescence even at very low dosages (50 nmoles). This damage to the effectiveness of thylakoids to generate proton gradients by ozone was enhanced by light and a secondary dark-dependent partial repair mechanism was detected. Experiments with mixed pollutants or their products revealed no ‘more than additive’ interactions between ozone plus sulphite or nitrite but the mixture of sulphite plus nitrite was a highly detrimental combination with synergistic effects detected at concentrations as low as 0·1 m m of each. These results would explain in large part the known sensitivity of photosynthetic reactions to ozone and to SO 2 plus NO 2 fumigations.