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 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 to the bolting phenotype. Metabolic profiling of the stem displayed 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 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 present in green stems. The results thus strongly suggest that NDB1 in the mitochondrial electron transport chain can, by modifying cell redox levels, specifically affect developmental processes.