AIR POLLUTANT STRESS CHANGES THE STEADY-STATE TRANSCRIPT LEVELS OF 3 PHOTOSYNTHESIS GENES

Six-week-old tobacco plants (Nicotiana tabacum L., cv. SR-1) were fumigated with different, but defined and realistic combinations of NO2, automobile exhaust and ozone for two days. To determine the effect of an additional environmental stress during exposure, plants were either wounded mechanically or treated with salicylic acid to simulate pathogen attack, he steady-state mRNA levels of genes encoding the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcS), chlorophyll a/b-binding protein (cab) and a 10 kDa protein of the water-evolving complex of photosystem II (ST-LS1) were probed in Northern analysis. Our results clearly show a decline of the mRNA levels for all three photosynthesis genes tinder automobile exhaust and/or ozone fumigation. Wounding and also elicitor treatment enhance this effect. In contrast, exposure to NO2 either increased the transcription level of all three genes, or counteracted the negative effect of automobile exhaust and ozone on their expression. At this time no major changes in the concentrations of the corresponding proteins could be detected by Western blot analyses. These results are discussed in the present paper.