title: Inter-relationships between light and respiration in the control of ascorbic acid synthesis and accumulation in Arabidopsis thaliana leaves.
abstract: The effects of growth irradiance and respiration on ascorbic acid (AA) synthesis and accumulation were studied in the leaves of wild-type and transformed Arabidopsis thaliana with modified amounts of the mitochondrial alternative oxidase (AOX) protein. Plants were grown under low (LL; 50 micromol photons m(-2) s(-1)), intermediate (IL; 100 micromol photons m(-2) s(-1)), or high (HL; 250 micromol photons m(-2) s(-1)) light. Increasing growth irradiance progressively elevated leaf AA content and hence the values of dark-induced disappearance of leaf AA, which were 11, 55, and 89 nmol AA lost g(-1) fresh weight h(-1), from LL-, IL-, and HL-grown leaves, respectively. When HL leaves were supplied with L-galactone-1,4-lactone (L-GalL; the precursor of AA), they accumulated twice as much AA and had double the maximal L-galactone-1,4-lactone dehydrogenase (L-GalLDH) activities of LL leaves. Growth under HL enhanced dehydroascorbate reductase and monodehydroascorbate reductase activities. Leaf respiration rates were highest in the HL leaves, which also had higher amounts of cytochrome c and cytochrome c oxidase (CCO) activities, as well as enhanced capacity of the AOX and CCO electron transport pathways. Leaves of the AOX-overexpressing lines accumulated more AA than wild-type or antisense leaves, particularly at HL. Intact mitochondria from AOX-overexpressing lines had higher AA synthesis capacities than those from the wild-type or antisense lines even though they had similar L-GalLDH activities. AOX antisense lines had more cytochrome c protein than wild-type or AOX-overexpressing lines. It is concluded that regardless of limitations on L-GalL synthesis by regulation of early steps in the AA synthesis pathway, the regulation of L-GalLDH activity via the interaction of light and respiratory controls is a crucial determinant of the overall ability of leaves to produce and accumulate AA.
authors.affiliation: Plant Physiology Institute (INFIVE), Schools of Agronomy and of Natural Sciences, National University of La Plata, La Plata, Argentina.
authors.forename: Carlos G
authors.initials: CG
authors.lastname: Bartoli
authors.forename: Jianping
authors.initials: J
authors.lastname: Yu
authors.forename: Facundo
authors.initials: F
authors.lastname: Gómez
authors.forename: Laura
authors.initials: L
authors.lastname: Fernández
authors.forename: Lee
authors.initials: L
authors.lastname: McIntosh
authors.forename: Christine H
authors.initials: CH
authors.lastname: Foyer
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology / Q000378:metabolism*; D001205:Ascorbic Acid / Q000096:biosynthesis* / Q000378:metabolism; D019069:Cell Respiration / Q000502:physiology; D003576:Electron Transport Complex IV / Q000502:physiology; D008027:Light; D024101:Mitochondrial Proteins; D010088:Oxidoreductases / Q000235:genetics / Q000502:physiology; D018515:Plant Leaves / Q000201:enzymology / Q000378:metabolism*; D010940:Plant Proteins; D030821:Plants, Genetically Modified / Q000378:metabolism; D000099188:Alternative Oxidase
chemical_list: D000975:Antioxidants; D001205:Ascorbic Acid; D003576:Electron Transport Complex IV; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D000099188:Alternative Oxidase