title: Constitutively expressed DHAR and MDHAR influence fruit, but not foliar ascorbate levels in tomato.
abstract: Vitamin C (L-ascorbate, AsA) is an essential nutrient required in key metabolic functions in humans and must be obtained from the diet, mainly from fruits and vegetables. Given its importance in human health and plant physiology we sought to examine the role of the ascorbate recycling enzymes monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) in tomato (Solanum lycopersicum), an economically important fruit crop. Cytosolic-targeted tomato genes Mdhar and Dhar were cloned and over-expressed under a constitutive promoter in tomato var. Micro-Tom. Lines with increased protein levels and enzymatic activity were identified and examined. Mature green and red ripe fruit from DHAR over-expressing lines had a 1.6 fold increase in AsA content in plants grown under relatively low light conditions (150 μmol m(-2) s(-1)). Conversely, MDHAR over-expressers had significantly reduced AsA levels in mature green fruits by 0.7 fold. Neither over-expressing line had altered levels of AsA in foliar tissues. These results underscore a complex regulation of the AsA pool size in tomato.
authors.affiliation: PIPRA, Department of Plant Sciences, University of California, Davis, CA 95616, USA.
authors.forename: Victor M
authors.initials: VM
authors.lastname: Haroldsen
authors.forename: Cecilia L
authors.initials: CL
authors.lastname: Chi-Ham
authors.forename: Shashank
authors.initials: S
authors.lastname: Kulkarni
authors.forename: Argelia
authors.initials: A
authors.lastname: Lorence
authors.forename: Alan B
authors.initials: AB
authors.lastname: Bennett
mesh_terms: D016960:Agrobacterium tumefaciens; D001205:Ascorbic Acid / Q000378:metabolism; D015153:Blotting, Western; D003001:Cloning, Molecular; D018274:Electroporation; D004789:Enzyme Activation; D057075:Enzyme Assays; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005638:Fruit / Q000235:genetics / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005822:Genetic Vectors / Q000235:genetics / Q000378:metabolism; D008027:Light; D018551:Solanum lycopersicum / Q000235:genetics* / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D010860:Pigments, Biological / Q000378:metabolism; D018515:Plant Leaves / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D054817:Pollination; D011401:Promoter Regions, Genetic
chemical_list: D010860:Pigments, Biological; D010088:Oxidoreductases; D009247:NADH, NADPH Oxidoreductases; C023927:monodehydroascorbate reductase (NADH); C020666:glutathione dehydrogenase (ascorbate); D001205:Ascorbic Acid