Nicotianamine, a plant-derived chelator of metals, is produced by the trimerization of S-adenosylmethionine catalyzed by nicotianamine synthase. We established transgenic Arabidopsis and tobacco plants that constitutively overexpress the barley nicotianamine synthase gene. Nicotianamine synthase overexpression resulted in increased biosynthesis of nicotianamine in transgenic plants, which conferred enhanced tolerance of high levels of metals, particularly nickel, to plants. Promoter activities of four nicotianamine synthase genes in Arabidopsis were all increased in response to excess nickel, suggesting that nicotianamine plays an important role in the detoxification of nickel in plants. Furthermore, transgenic tobacco plants with a high level of nicotianamine grew well in a nickel-enriched serpentine soil without developing any symptoms of nickel toxicity. Our results indicate that nicotianamine plays a critical role in metal detoxification, and this can be a powerful tool for use in phytoremediation.
During the screening for the inhibitors of protein kinase C (PKC), we found that a streptomycete produced an inhibitor in our bleb-forming assay (Osada et al, J. Antibiotics 41 : 925, 1988). The inhibitor was isolated and identified as sangivamycin (4-amino-5-carboxamide-7-(D-ribofuranosyl)pyrrolo[2,3-d]pyrimidine). Biological activity of sangivamycin was compared with that of other 7-deazaadenosine group antibiotics, tubercidin and toyocamycin. Sangivamycin showed a strong inhibitory activity against bleb-formation of K562 cells and PKC. On the other hand, tubercidin and toyocamycin had only weak activities in both assays. This paper deals with a new biological activity of sangivamycin, that of an inhibitor of protein kinases, especially PKC.
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