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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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Accumulation pattern of cytokinins in rice roots and shoots in response to nitrate and 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 culture media containing 1 mM NH4Cl, 1 mM KNO3 or 1 mM KCl. After the time indicated, roots and shoots were separately harvested in triplicate, and the cytokinin contents were quantified. The value in each block indicates the concentration (mean values) as pmol g−1 FW. The relative accumulation level of each compound compared with the accumulation in the KCl treatment is color-coded. BQ, below the quantification limit. *P < 0.05; **P < 0.01 (Student’s t-test, comparison with the KCl treatment). The complete data set is presented in Supplementary Tables S1 and S2.
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pct127-F1: Accumulation pattern of cytokinins in rice roots and shoots in response to nitrate and 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 culture media containing 1 mM NH4Cl, 1 mM KNO3 or 1 mM KCl. After the time indicated, roots and shoots were separately harvested in triplicate, and the cytokinin contents were quantified. The value in each block indicates the concentration (mean values) as pmol g−1 FW. The relative accumulation level of each compound compared with the accumulation in the KCl treatment is color-coded. BQ, below the quantification limit. *P < 0.05; **P < 0.01 (Student’s t-test, comparison with the KCl treatment). The complete data set is presented in Supplementary Tables S1 and S2.

Mentions: To examine whether nitrogen nutrition affects cytokinin metabolism in rice, cytokinins and their conjugates were quantified in rice seedlings after supplement of nitrate or ammonium. In roots and shoots, iP riboside 5′-phosphates (iPRPs) and tZ riboside 5′-phosphates (tZRPs), early products of de novo cytokinin synthesis, accumulated following exposure to both nitrogen sources (Fig. 1; Supplementary Tables S1, S2). Similar patterns were observed in the nucleosides and active-form nucleobases, iP riboside (iPR), iP and tZ riboside (tZR), whereas tZ was below the quantification limit at all times. The accumulation of transcripts of cytokinin-responsive type-A response regulator genes was also increased in roots (Supplementary Fig. S1). On the other hand, there was no apparent increase in cZ, cZ riboside (cZR) and cZR 5′-phosphates (cZRPs). These results suggested that exposure to inorganic nitrogen sources activated the de novo synthesis of tZ- and iP-type cytokinins in rice.Fig. 1


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)

Accumulation pattern of cytokinins in rice roots and shoots in response to nitrate and 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 culture media containing 1 mM NH4Cl, 1 mM KNO3 or 1 mM KCl. After the time indicated, roots and shoots were separately harvested in triplicate, and the cytokinin contents were quantified. The value in each block indicates the concentration (mean values) as pmol g−1 FW. The relative accumulation level of each compound compared with the accumulation in the KCl treatment is color-coded. BQ, below the quantification limit. *P < 0.05; **P < 0.01 (Student’s t-test, comparison with the KCl treatment). The complete data set is presented in Supplementary Tables S1 and S2.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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

pct127-F1: Accumulation pattern of cytokinins in rice roots and shoots in response to nitrate and 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 culture media containing 1 mM NH4Cl, 1 mM KNO3 or 1 mM KCl. After the time indicated, roots and shoots were separately harvested in triplicate, and the cytokinin contents were quantified. The value in each block indicates the concentration (mean values) as pmol g−1 FW. The relative accumulation level of each compound compared with the accumulation in the KCl treatment is color-coded. BQ, below the quantification limit. *P < 0.05; **P < 0.01 (Student’s t-test, comparison with the KCl treatment). The complete data set is presented in Supplementary Tables S1 and S2.
Mentions: To examine whether nitrogen nutrition affects cytokinin metabolism in rice, cytokinins and their conjugates were quantified in rice seedlings after supplement of nitrate or ammonium. In roots and shoots, iP riboside 5′-phosphates (iPRPs) and tZ riboside 5′-phosphates (tZRPs), early products of de novo cytokinin synthesis, accumulated following exposure to both nitrogen sources (Fig. 1; Supplementary Tables S1, S2). Similar patterns were observed in the nucleosides and active-form nucleobases, iP riboside (iPR), iP and tZ riboside (tZR), whereas tZ was below the quantification limit at all times. The accumulation of transcripts of cytokinin-responsive type-A response regulator genes was also increased in roots (Supplementary Fig. S1). On the other hand, there was no apparent increase in cZ, cZ riboside (cZR) and cZR 5′-phosphates (cZRPs). These results suggested that exposure to inorganic nitrogen sources activated the de novo synthesis of tZ- and iP-type cytokinins in rice.Fig. 1

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