The Effect of Elevated Concentrations of Fructose 2,6-Bisphosphate on Carbon Metabolism during Deacidification in the Crassulacean Acid Metabolism Plant Kalanchöe daigremontiana

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Abstract
In C3 plants, the metabolite fructose 2,6-bisphosphate (Fru 2,6-P2) has an important role in the regulation of carbon partitioning during photosynthesis. To investigate the impact of Fru 2,6-P2 on carbon metabolism during Crassulacean acid metabolism (CAM), we have developed an Agrobacterium tumefaciens-mediated transformation system in order to alter genetically the obligate CAM plant Kalanchöe daigremontiana. To our knowledge, this is the first report to use genetic manipulation of a CAM species to increase our understanding of this important form of plant metabolism. Transgenic plants were generated containing a modified rat liver 6-phosphofructo-2-kinase gene. In the plants analyzed the activity of 6-phosphofructo-2-kinase ranged from 175% to 198% of that observed in wild-type plants, resulting in Fru 2,6-P2 concentrations that were 228% to 350% of wild-type plants after 2 h of illumination. A range of metabolic measurements were made on these transgenic plants to investigate the possible roles of Fru 2,6-P2 during Suc, starch, and malic acid metabolism across the deacidification period of CAM. The results suggest that Fru 2,6-P2 plays a major role in regulating partitioning between Suc and starch synthesis during photosynthesis. However, alterations in Fru 2,6-P2 levels had little effect on malate mobilization during CAM fluxes.