Effects of Elevated CO(2) on Levels of Primary Metabolites and Transcripts of Genes Encoding Respiratory Enzymes and Their Diurnal Patterns in Arabidopsis thaliana: Possible Relationships with Respiratory Rates

Elevated CO(2) affects plant growth and photosynthesis, which results in changes in plant respiration. However, the mechanisms underlying the responses of plant respiration to elevated CO(2) are poorly understood. In this study, we measured diurnal changes in the transcript levels of genes encoding respiratory enzymes, the maximal activities of the enzymes and primary metabolite levels in shoots of Arabidopsis thaliana grown under moderate or elevated CO(2) conditions (390 or 780 parts per million by volume CO(2), respectively). We examined the relationships between these changes and respiratory rates. Under elevated CO(2), the transcript levels of several genes encoding respiratory enzymes increased at the end of the light period, but these increases did not result in changes in the maximal activities of the corresponding enzymes. The levels of some primary metabolites such as starch and sugar phosphates increased under elevated CO(2), particularly at the end of the light period. The O(2) uptake rate at the end of the dark period was higher under elevated CO(2) than under moderate CO(2), but higher under moderate CO(2) than under elevated CO(2) at the end of the light period. These results indicate that the changes in O(2) uptake rates are not directly related to changes in maximal enzyme activities and primary metabolite levels. Instead, elevated CO(2) may affect anabolic processes that consume respiratory ATP, thereby affecting O(2) uptake rates.