Does the Krebs Cycle Reduce Photosynthesis?
Although the operation and location of the Krebs cycle was demonstrated in plant cells decades ago, many fundamental questions remain concerning how its activity is integrated with other plant processes. For example, controversy exists over whether the Krebs cycle operates in illuminated photosynthetic tissue and if it contributes to the energy requirements for the synthesis of Suc in photosynthetic tissues. In this issue, Carrari et al. (pp. 1322 1335) describe the molecular and genetic analysis of Aco-1, a Lycopersicon pennellii accession that is deficient in aconitase, the Krebs cycle enzyme that catalyzes the reversible interconversion of citrate and isocitrate. As expected, the mutation resulted in lowered expression of the Aco-1 transcript and lowered levels of both cytosolic and mitochondrial aconitase protein and activity. Biochemical analysis of leaves of the Aco-1 accession suggested that they exhibited a restricted flux through the Krebs cycle and reduced levels of Krebs cyc
