- Interconversions of different forms of vitamin B6 in tobacco plants
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There are six different vitamin B6 (VB6) forms, pyridoxal (PL), pyridoxamine (PM), pyridoxine (PN), pyridoxal 5′-phosphate (PLP), pyridoxamine 5′-phosphate (PMP), and pyridoxine 5′-phosphate (PNP), of which PLP is the active form. Although plants are a major source of VB6 in the human diet, and VB6 plays an important role in plants, the mechanisms underlying the interconversions of different VB 6 forms are not well understood. In this study, in vitro tobacco plants were grown on Murashige and Skoog (MS) basal media supplemented with 100 mg/L of PM, PL or PN and the abundance of the different B6 vitamers in leaf tissue was quantified by high performance liquid chromatography (HPLC). The total amount of VB6 was about 3.9 μg/g fresh weight of which PL, PM, PN, PLP and PMP accounted for 23%, 14%, 37%, 20% and 6%, respectively. Tobacco plants contained a trace amount of PNP. Supplementation of the culture medium with any of the non-phosphorylated vitamers resulted in an increase in total VB6 by about 10-fold, but had very little impact on the concentrations of the endogenous phosphorylated vitamers. Administration of either PM or PN increased their endogenous levels more than the levels of any other endogenous B6 vitamers. PL supplementation increased the levels of plant PN and PM significantly, but not that of PL, suggesting that efficient conversion pathways from PL to PN and PM are present in tobacco. Additionally, maintenance of a stable level of PLP in the plant is not well-correlated to changes in levels of non-phosphorylated forms.
- Huang, Shuohao,Zeng, Haibin,Zhang, Jianyun,Wei, Shu,Huang, Longquan
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- Cloning of the pyridoxine 5′-phosphate phosphatase gene (pdxP) and vitamin B6 production in pdxP recombinant Sinorhizobium meliloti
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A novel gene (pdxP) encoding a pyridoxine 5′-phosphate (PNP) phosphatase involved in the last step of pyridoxine biosynthesis was cloned from Sinorhizobium meliloti IFO 14782 on the basis of the peptide sequences of the natural enzyme. The pdxP gene is an open reading frame (708 bp) encoding 235 amino acid residues with a calculated molecular weight of 26,466. From its deduced amino acid sequence, it was predicted that the enzyme belongs to the haloacid dehalogenase superfamily. Transformants of Escherichia coli and S. meliloti by pdxP gene expression plasmids showed stimulated PNP phosphatase activities. When pdxP was over-expressed together with the PNP synthase gene (pdxJ) in S. meliloti, the recombinant strain produced 149 mg/l of pyridoxine, 46% and 16% higher than the host strain and the pdxJ recombinant of S. meliloti respectively.
- Nagahashi, Yoshie,Tazoe, Masaaki,Hoshino, Tatsuo
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