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Nitrogen-dependent regulation of de novo cytokinin biosynthesis in rice: the role of glutamine metabolism as an additional signal.

Kamada-Nobusada T, Makita N, Kojima M, Sakakibara H - Plant Cell Physiol. (2013)

Bottom Line: In this study, we have identified another regulatory system of cytokinin de novo biosynthesis in response to nitrogen status.In rice, OsIPT4, OsIPT5, OsIPT7 and OsIPT8 were up-regulated in response to exogenously applied nitrate and ammonium, with accompanying accumulation of cytokinins.In transgenic lines repressing the expression of OsIPT4, which is the dominant IPT in rice roots, the nitrogen-dependent increase of cytokinin in the xylem sap was significantly reduced, and seedling shoot growth was retarded despite sufficient nitrogen.

View Article: PubMed Central - PubMed

Affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi, Yokohama, 230-0045 Japan.

ABSTRACT
Cytokinin activity in plants is closely related to nitrogen availability, and an Arabidopsis gene for adenosine phosphate-isopentenyltransferase (IPT), IPT3, is regulated by inorganic nitrogen sources in a nitrate-specific manner. In this study, we have identified another regulatory system of cytokinin de novo biosynthesis in response to nitrogen status. In rice, OsIPT4, OsIPT5, OsIPT7 and OsIPT8 were up-regulated in response to exogenously applied nitrate and ammonium, with accompanying accumulation of cytokinins. Pre-treatment of roots with l-methionine sulfoximine, a potent inhibitor of glutamine synthetase, abolished the nitrate- and ammonium-dependent induction of OsIPT4 and OsIPT5, while glutamine application induced their expression. Thus, neither nitrate nor ammonium, but glutamine or a related metabolite, is essential for the induction of these IPT genes in rice. On the other hand, glutamine-dependent induction of IPT3 occurs in Arabidopsis, at least to some extent. In transgenic lines repressing the expression of OsIPT4, which is the dominant IPT in rice roots, the nitrogen-dependent increase of cytokinin in the xylem sap was significantly reduced, and seedling shoot growth was retarded despite sufficient nitrogen. We conclude that plants possess multiple regulation systems for nitrogen-dependent cytokinin biosynthesis to modulate growth in response to nitrogen availability.

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Changes in the concentrations of free amino acids in rice roots after application of ammonium. Rice seedlings were hydroponically grown in tap water for 11 d after sowing and transferred to nitrogen-free culture medium for 3 d. Then, the roots were dipped into the culture medium containing 1 mM KCl (light gray) or 1 mM NH4Cl (dark gray) for 30 min. Roots were harvested in triplicate, and the amino acid contents were analyzed. Bars represent mean values with the SD. The detailed data are provided in Supplementary Table S3.
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pct127-F7: Changes in the concentrations of free amino acids in rice roots after application of ammonium. Rice seedlings were hydroponically grown in tap water for 11 d after sowing and transferred to nitrogen-free culture medium for 3 d. Then, the roots were dipped into the culture medium containing 1 mM KCl (light gray) or 1 mM NH4Cl (dark gray) for 30 min. Roots were harvested in triplicate, and the amino acid contents were analyzed. Bars represent mean values with the SD. The detailed data are provided in Supplementary Table S3.

Mentions: Next, we analyzed the responses of amino acid concentrations in rice roots to inorganic nitrogen sources. Rice seedlings were grown for 2 weeks after germination without a nitrogen source, before ammonium or nitrate were supplemented. Upon exposure to ammonium, glutamine accumulated drastically in the roots within 30 min, and increased further over 2 h (Fig. 7; Supplementary Table S3). On the other hand, concentrations of aspartic and glutamic acids were decreased, and other amino acids showed no significant effects. In the nitrate treatment, a small but increased concentration of glutamine was also observed (Supplementary Table S3). These results were consistent with the positive effects of exogenously applied glutamine on the induction of OsIPT4 and OsIPT5 expression.Fig. 7


Nitrogen-dependent regulation of de novo cytokinin biosynthesis in rice: the role of glutamine metabolism as an additional signal.

Kamada-Nobusada T, Makita N, Kojima M, Sakakibara H - Plant Cell Physiol. (2013)

Changes in the concentrations of free amino acids in rice roots after application of ammonium. Rice seedlings were hydroponically grown in tap water for 11 d after sowing and transferred to nitrogen-free culture medium for 3 d. Then, the roots were dipped into the culture medium containing 1 mM KCl (light gray) or 1 mM NH4Cl (dark gray) for 30 min. Roots were harvested in triplicate, and the amino acid contents were analyzed. Bars represent mean values with the SD. The detailed data are provided in Supplementary Table S3.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3814184&req=5

pct127-F7: Changes in the concentrations of free amino acids in rice roots after application of ammonium. Rice seedlings were hydroponically grown in tap water for 11 d after sowing and transferred to nitrogen-free culture medium for 3 d. Then, the roots were dipped into the culture medium containing 1 mM KCl (light gray) or 1 mM NH4Cl (dark gray) for 30 min. Roots were harvested in triplicate, and the amino acid contents were analyzed. Bars represent mean values with the SD. The detailed data are provided in Supplementary Table S3.
Mentions: Next, we analyzed the responses of amino acid concentrations in rice roots to inorganic nitrogen sources. Rice seedlings were grown for 2 weeks after germination without a nitrogen source, before ammonium or nitrate were supplemented. Upon exposure to ammonium, glutamine accumulated drastically in the roots within 30 min, and increased further over 2 h (Fig. 7; Supplementary Table S3). On the other hand, concentrations of aspartic and glutamic acids were decreased, and other amino acids showed no significant effects. In the nitrate treatment, a small but increased concentration of glutamine was also observed (Supplementary Table S3). These results were consistent with the positive effects of exogenously applied glutamine on the induction of OsIPT4 and OsIPT5 expression.Fig. 7

Bottom Line: In this study, we have identified another regulatory system of cytokinin de novo biosynthesis in response to nitrogen status.In rice, OsIPT4, OsIPT5, OsIPT7 and OsIPT8 were up-regulated in response to exogenously applied nitrate and ammonium, with accompanying accumulation of cytokinins.In transgenic lines repressing the expression of OsIPT4, which is the dominant IPT in rice roots, the nitrogen-dependent increase of cytokinin in the xylem sap was significantly reduced, and seedling shoot growth was retarded despite sufficient nitrogen.

View Article: PubMed Central - PubMed

Affiliation: RIKEN Center for Sustainable Resource Science, Tsurumi, Yokohama, 230-0045 Japan.

ABSTRACT
Cytokinin activity in plants is closely related to nitrogen availability, and an Arabidopsis gene for adenosine phosphate-isopentenyltransferase (IPT), IPT3, is regulated by inorganic nitrogen sources in a nitrate-specific manner. In this study, we have identified another regulatory system of cytokinin de novo biosynthesis in response to nitrogen status. In rice, OsIPT4, OsIPT5, OsIPT7 and OsIPT8 were up-regulated in response to exogenously applied nitrate and ammonium, with accompanying accumulation of cytokinins. Pre-treatment of roots with l-methionine sulfoximine, a potent inhibitor of glutamine synthetase, abolished the nitrate- and ammonium-dependent induction of OsIPT4 and OsIPT5, while glutamine application induced their expression. Thus, neither nitrate nor ammonium, but glutamine or a related metabolite, is essential for the induction of these IPT genes in rice. On the other hand, glutamine-dependent induction of IPT3 occurs in Arabidopsis, at least to some extent. In transgenic lines repressing the expression of OsIPT4, which is the dominant IPT in rice roots, the nitrogen-dependent increase of cytokinin in the xylem sap was significantly reduced, and seedling shoot growth was retarded despite sufficient nitrogen. We conclude that plants possess multiple regulation systems for nitrogen-dependent cytokinin biosynthesis to modulate growth in response to nitrogen availability.

Show MeSH
Related in: MedlinePlus