title: NAD malic enzyme and the control of carbohydrate metabolism in potato tubers.
abstract: Potato (Solanum tuberosum) plants were transformed with a cDNA encoding the 59-kD subunit of the potato tuber NAD-dependent malic enzyme (NADME) in the antisense orientation. Measurements of the maximum catalytic activity of NADME in tubers revealed a range of reductions in the activity of this enzyme down to 40% of wild-type activity. There were no detrimental effects on plant growth or tuber yield. Biochemical analyses of developing tubers indicated that a reduction in NADME activity had no detectable effects on flux through the tricarboxylic acid cycle. However, there was an effect on glycolytic metabolism with significant increases in the concentration of 3-phosphoglycerate and phosphoenolpyruvate. These results suggest that alterations in the levels of intermediates toward the end of the glycolytic pathway may allow respiratory flux to continue at wild-type rates despite the reduction in NADME. There was also a statistically significant negative correlation between NADME activity and tuber starch content, with tubers containing reduced NADME having an increased starch content. The effect on plastid metabolism may result from the observed glycolytic perturbations.
authors.affiliation: Department of Plant Sciences, University of Oxford, South Parks Road, Oxford OX1 3RB, United Kingdom.
authors.forename: H L
authors.initials: HL
authors.lastname: Jenner
authors.forename: B M
authors.initials: BM
authors.lastname: Winning
authors.forename: A H
authors.initials: AH
authors.lastname: Millar
authors.forename: K L
authors.initials: KL
authors.lastname: Tomlinson
authors.forename: C J
authors.initials: CJ
authors.lastname: Leaver
authors.forename: S A
authors.initials: SA
authors.lastname: Hill
mesh_terms: D050260:Carbohydrate Metabolism; D002244:Carbon / Q000378:metabolism; D002384:Catalysis; D019069:Cell Respiration; D002952:Citric Acid Cycle; D005988:Glyceric Acids / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D010728:Phosphoenolpyruvate / Q000378:metabolism; D011198:Solanum tuberosum / Q000201:enzymology*; D013213:Starch / Q000378:metabolism
chemical_list: D005988:Glyceric Acids; D010728:Phosphoenolpyruvate; D002244:Carbon; C005156:3-phosphoglycerate; D013213:Starch; D008291:Malate Dehydrogenase; C046446:malate dehydrogenase-(oxaloacetate-decarboxylating) (NAD+)