Normal growth of transgenic tobacco plants in the absence of cytosolic pyruvate kinase

The coding sequence of the cytosolic isozyme of potato tuber pyruvate kinase (PK) was attached to the transit peptide of the small subunit of pea ribulose-1,5-bisphosphate carboxylase oxygenase and placed under the control of the cauliflower mosaic virus 35S promoter. This construct was transformed into Nicotiana tabacum. Unexpectedly, two primary transformants were recovered in which PK activity in leaves was greatly reduced. The reduction in PK activity appeared to result from the complete absence of the cytosolic form of the enzyme (PK_c). In addition, no PK_c could be detected on western blots of leaf extracts. Metabolite analyses indicated that the levels of phosphoenolpyruvate are substantially higher in PK_c-deficient leaves than in wild-type leaves, consistent with a block in glycolysis at the step catalyzed by PK. PK_c deficiency in the leaves does not appear to adversely affect plant growth. Analysis of progeny indicates that PK_c deficiency is a heritable trait. The leaves of PK_c-deficient transformants have normal rates of photosynthetic O₂ evolution and respiratory O₂ consumption, indicating that these plants are using alternative pathways to bypass PK.