PARENT SESSION
Posters P2C Carbon and nitrogen interactions. Abstracts (614-616)

Impact of photosynthesis and respiration on the integration of carbon and nitrogen metabolism. Graham Noctor^*,1, Christelle Dutilleul², Simon Driscoll², Rosine De Paepe¹, Christine Foyer², ¹ Institut de Biotechnologie des Plantes, Orsay, France² Crop Performance and Improvement, Harpenden, Hertfordshire, UK

ABSTRACT- In C3 plants, foliar nitrogen assimilation occurs alongside photorespiration, and involves complex interactions between mitochondria, chloroplasts, peroxisomes, and cytosol in the production and use of amino acids, organic acids, and reductant. Fuller understanding of these interactions is required in order to target components for optimization, and exploitation of the new techniques of metabolomics requires improved insight into factors governing major metabolite contents in leaves. By using a simple modelling approach to estimate photorespiratory rates in wheat and potato leaves photosynthesizing under defined conditions, and rapid-quench techniques to stop metabolism, it is shown that certain amino acids (Gly, Asp, Ala) are strongly influenced by photorespiration, whereas the initial organic product of ammonia assimilation (Gln) is not. The Gly/Ser ratio and Asp contents are good markers for photorespiration, but Gln and the Gln/Glu ratio appear to respond more strongly to imbalances in the relative rates of supply of net ammonia and 2-oxoglutarate synthesis [Novitskaya et al. (2002) Plant Cell Environ 25, 821]. Although uninfluenced by photosynthetic processes in the short-term, minor amino acid contents are highly co-ordinated in leaves, suggesting some form of general control of amino acid synthesis in plants [Noctor et al. (2002) J Exp Bot 53, 939]. Analysis of a Nicotiana sylvestris mutant lacking functional mitochondrial Complex I shows that under non-photorespiratory conditions, photosynthesis is not affected by lack of this NADH dehydrogenase but is significantly decreased in air. This suggests that NADH re-oxidation by the mitochondrial electron transport chain is a necessary process during C3 photosynthesis [Dutilleul et al. (2003) Plant Physiol 131, 264]. Furthermore, metabolite profiling of the mutant shows a strong shift in carbon/nitrogen relationships, with accumulation of N-rich amino acids and modifications in key C metabolites. These and other measurements suggest that Complex I is an NADH sink that is crucial in co-ordinating rates of organic acid production with rates of cytosolic nitrate reduction.

KEY WORDS: General control of amino acid synthesis, Metabolite profiling, Photorespiration, Mitochondrial electron transport mutant