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BIOENERGETICS AND PHOTOSYNTHESIS

A Redox-Mediated Modulation of Stem Bolting in Transgenic Nicotiana sylvestris Differentially Expressing the External Mitochondrial NADPH Dehydrogenase^1,[W],[OA]

Department of Cell and Organism Biology, Lund University, SE–22362 Lund, Sweden (Y.-J.L., S.V.W., I.L., A.M.M., F.E.B.N., S.W., A.G.R.); Max-Planck-Institut für Molekulare Pflanzenphysiologie, 14476 Potsdam-Golm, Germany (A.N.-N., A.R.F.); and Syngenta Seeds AB, SE–26123 Landskrona, Sweden (K.M.F.)

Cytosolic NADPH can be directly oxidized by a calcium-dependent NADPH dehydrogenase, NDB1, present in the plant mitochondrial electron transport chain. However, little is known regarding the impact of modified cytosolic NADPH reduction levels on growth and metabolism. Nicotiana sylvestris plants overexpressing potato (Solanum tuberosum) NDB1 displayed early bolting, whereas sense suppression of the same gene led to delayed bolting, with consequential changes in flowering time. The phenotype was dependent on light irradiance but not linked to any change in biomass accumulation. Whereas the leaf NADPH/NADP⁺ ratio was unaffected, the stem NADPH/NADP⁺ ratio was altered following the genetic modification and strongly correlated with the bolting phenotype. Metabolic profiling of the stem showed that the NADP(H) change affected relatively few, albeit central, metabolites, including 2-oxoglutarate, glutamate, ascorbate, sugars, and hexose-phosphates. Consistent with the phenotype, the modified NDB1 level also affected the expression of putative floral meristem identity genes of the SQUAMOSA and LEAFY types. Further evidence for involvement of the NADPH redox in stem development was seen in the distinct decrease in the stem apex NADPH/NADP⁺ ratio during bolting. Additionally, the potato NDB1 protein was specifically detected in mitochondria, and a survey of its abundance in major organs revealed that the highest levels are found in green stems. These results thus strongly suggest that NDB1 in the mitochondrial electron transport chain can, by modifying cell redox levels, specifically affect developmental processes.

² Present address: Institute of Crop Sciences, Chinese Academy of Agricultural Sciences, Beijing 100081, China.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Allan G. Rasmusson (allan.rasmusson{at}cob.lu.se).

^[W] The online version of this article contains Web-only data.

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www.plantphysiol.org/cgi/doi/10.1104/pp.109.136242

^* Corresponding author; e-mail allan.rasmusson{at}cob.lu.se.

Received January 26, 2009; accepted May 4, 2009; published May 8, 2009.

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