Project 3 - Photosynthetic carbon metabolism in an Arabidopsis mutant deficient in a major chloroplast envelope transporter

During photosynthesis organic carbon is exported from the chloroplast principally in the from of triose-phosphates which provide the substrate for sucrose formation in the cytosol. This export occurs through a specialised triose-phosphate/phosphate translocator which is capable of catalysing the strict one-for-one counter-exchange of triose-P, 3-phosphoglycerate and inorganic phosphate (Pi) across the chloroplast envelope. Recently we have identified a "knockout" mutant in arabidopsis in which the expression of the unique gene encoding this transporter has been abolished. Despite this change the mutant plant apparently grows normally under low light conditions.

The aim of this project is to investigate the effect of this gene disruption on photosynthetic carbon partitioning. The work is likely to involve: the use of enzymic assays to determine the levels of metabolic intermediates and the signal metabolite fructose 2,6-bisphosphate in illuminated leaves throughout the photoperiod, and analysis of the distribution of radioactivity in the major classes of metabolites following photosynthesis in 14CO2 to determine the partitioning of photoassimilates. Further pulse-chase experiments would be performed to investigate the major route for export of carbon from chloroplasts in the light. Details of the approaches and techniques to be used can be found in our previous publications (Scott, P., Lange, A.J., Pilkis, S.J. and Kruger, N.J. (1995) Carbon metabolism in leaves of transgenic tobacco (Nicotiana tabacum L.) containing elevated fructose 2,6-bisphosphate levels. Plant J. 7, 101-109 and Scott, P., Lange, A.J. and Kruger, N.J. (2000) Photosynthetic carbon metabolism in leaves of transgenic tobacco (Nicotiana tabacum L.) containing decreased amounts of fructose 2,6-bisphosphate. Planta 211, 864-873). The work is aimed at explaining how carbon metabolism compensates for the disruption of a major pathway allowing photosynthesis to continue at optimal wildtype rates. It is unlikely that the whole of such an analysis would be completed within the framework of a single undergraduate project!

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