Abstract

We examined the effects of moderately elevated ozone at an open-air field on protein expression patterns in the leaves of two Finnish hybrid aspen (Populus tremula L. x Populus tremuloides Michx.) clones with different O3 sensitivities. The soil-grown plants were exposed for three growing seasons to O3 1.3 to 1.4 times the ambient concentration (approximately 35 ppb), mirroring increases expected in the near future. Contrary to our expectations, O3 treatment had no major effects on the protein patterns of the two hybrid aspen clones. Altogether, 447 protein spots were reproducibly detected in the SYPRO Ruby -stained gels. The intensity of nine of these spots was significantly affected by O3; six and three were up- and down-regulated, respectively. In both clones, chronic long-term O3 stress up-regulated WRKY transcription factor and a Myb protein and transposon protein. The clones showed contrasting responses in RuBisCO large subunit fragment, thioredoxin (TRX) intermediate and glyceraldehyde phosphate dehydrogenase (GPDH). In the more tolerant clone 55, RuBisCO large subunit fragment and TRX were down-regulated and GPDH up-regulated, while in the more sensitive clone RuBisCO large subunit fragment and TRX were up-regulated and GPDH down-regulated. Although our study found rather small changes in hybrid aspen proteome, it showed the significance of long-term O3 exposure on growing trees. This study would prove useful to scale up O3 responses on mature trees at the ecosystem level.

Keywords: Aspen, FACE, ozone, proteomics.