9420054 Seemann The concentration of carbon dioxide in the earth's atmosphere is projected to double by the middle to end of the 21st century. This change will have substantial effects on natural and agricultural ecosystems, primarily because of the effect of carbon dioxide on photosynthesis, the major biological process in the global carbon cycle. In many plant species, long-term growth at elevated atmospheric carbon dioxide results in the substantial change in both absolute photosynthetic capacity and the protein composition of the photosynthetic apparatus. However, the molecular mechanism(s) by which external carbon dioxide concentration acts at the level of gene expression, are largely unknown. The overall objective of this research is to link carbon dioxide effects on photosynthetic physiological processes (e.g. leaf gas exchange) and biochemical processes (e.g. rubisco protein level and regulation of activity) to changes in both rubisco gene expression and specific carbohydrate levels in order to identify molecular mechanisms which control the response of plants to elevated carbon dioxide. Arabidopsis thaliana (wild-type and existing mutants) will be used as the model plant system. Specific objectives are: (1) Determine the effect of atmospheric carbon dioxide concentration during different developmental stages on rubisco large subunit (rbcL) and small subunit (rbcS) gene expression, rubisco holoenzyme level, activation state, RuBP pool size and the response of photosynthesis to intercellular carbon dioxide partial pressure (Ci) in Arabidopsis thaliana grown at and switched between a number of carbon dioxide concentrations (subambient, ambient, twice ambient, saturating). (2) Identify the cellular signal(s) that function(s) in the signal transduction pathway between atmospheric carbon dioxide concentration and rubisco gene expression by utilizing (1) mutants of Arabidopsis thaliana with altered source or sink activities (altered leaf carbohydra te metabolism, no seed production, altered root:shoot ratio, delayed flowereing time) in studies of carbon dioxide effects on rubisco gene expression and photosynthesis, and; (2) transient expression studies of carbohydrate effects on rbcS promoter-GUS constructs.
