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          Institute: MPI für molekulare Pflanzenphysiologie     Collection: Publikationen Pflanzenphysiologie     Display Documents

ID: 224222.0, MPI für molekulare Pflanzenphysiologie / Publikationen Pflanzenphysiologie
Altered activity of the P2 isoform of plastidic glucose 6-phosphate dehydrogenase in tobacco (Nicotiana tabacum cv. Samsun) causes changes in carbohydrate metabolism and response to oxidative stress in leaves
Authors:Debnam, P. M.; Fernie, A. R.; Leisse, A.; Golding, A.; Bowsher, C. G.; Grimshaw, C.; Knight, J. S.; Emes, M. J.
Date of Publication (YYYY-MM-DD):2004-04
Title of Journal:Plant Journal
Journal Abbrev.:Plant J
Issue / Number:1
Start Page:49
End Page:59
Review Status:not specified
Audience:Not Specified
Abstract / Description:Expression of one specific isoform of plastidic glucose 6-phosphate dehydrogenase (G6PDH) was manipulated in transgenic tobacco. Antisense and sense constructs of the endogenous P2 form of G6PDH were used to transform plants under the control of the cauliflower mosaic virus (CaMV) 35S promotor. Recombinant plants with altered expression were taken through to homozygosity by selective screening. Northern analyses revealed substantial changes in the expression of the P2 form of G6PDH, with no apparent impact on the activity of the cytosolic isoenzyme. Analysis of G6PDH activity in chloroplasts showed that despite the large changes in expression of P2-G6PDH, the range of enzyme activity varied only from approximately 50 to 200% of the wild type, reflecting the presence of a second G6PDH chloroplastic isoform (P1). Although none of the transgenic plants showed any visible phenotype, there were marked differences in metabolism of both sense and antisense lines when compared with wild-type/control lines. Sucrose, glucose and fructose contents of leaves were higher in antisense lines, whereas in overexpressing lines, the soluble sugar content was reduced below that of control plants. Even more striking was the observation that contents of glucose 6-phosphate (Glc6P) and 6-phosphogluconate (6PG) changed, such that the ratio of Glc6P:6PG was some 2.5-fold greater in the most severe antisense lines, compared with those with the highest levels of overexpression. Because of the distinctive biochemical properties of P2-G6PDH, we investigated the impact of altered expression on the contents of antioxidants and the response of plants to oxidative stress induced by methyl viologen (MV). Plants with decreased expression of P2-G6PDH showed increased content of reduced glutathione (GSH) compared to other lines. They also possessed elevated contents of ascorbate and exhibited a much higher ratio of reduced:oxidised ascorbate. When exposed to MV, leaf discs of wild-type and overexpressing lines demonstrated increased oxidative damage as measured by lipid peroxidation. Remarkably, leaf discs from plants with decreased P2-G6PDH did not show any change in lipid peroxidation in response to increasing concentrations of up to 15 mum MV. The results are discussed from the perspective of the role of G6PDH in carbohydrate metabolism and oxidative stress. It is suggested that the activity of P2-G6PDH may be crucial in balancing the redox poise in chloroplasts.
Free Keywords:glucose 6-phosphate dehydrogenase
; oxidative pentose phosphate pathway
; carbohydrate
; antioxidants
; chloroplasts
; adp-glucose pyrophosphorylase
; transgenic tobacco
; starch synthesis
; glutathione-reductase
; sensitive method
; potato-tuber
; chloroplasts
; ascorbate
; plants
; protein
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für molekulare Pflanzenphysiologie/Molekulare Physiologie/AG Willmitzer/Fernie
External Affiliations:Univ Guelph, Coll Biol Sci, Gordon St, Guelph, ON N1G 2W1, Canada
Univ Guelph, Coll Biol Sci, Guelph, ON N1G 2W1, Canada
Max Planck Inst Mol Plant Physiol, D-14766 Golm, Germany
Univ Manchester, Sch Biol Sci, Manchester M13 9PT, Lancs, England
Ag Res Wallaceville, Wellington, New Zealand
Identifiers:ISI:000220521800005 [ID No:1]
ISI:000220521800005 [ID No:2]
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