Cytokinins are central regulators of cambial activity

  • Miho Matsumoto-Kitano
    Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan;
  • Takami Kusumoto
    Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan;
  • Petr Tarkowski
    Department of Biochemistry, Faculty of Science, Palacky University, Slechtitelu 11, Olomouc 78371, Czech Republic; and
  • Kaori Kinoshita-Tsujimura
    Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan;
  • Kateřina Václavíková
    Department of Biochemistry, Faculty of Science, Palacky University, Slechtitelu 11, Olomouc 78371, Czech Republic; and
  • Kaori Miyawaki
    Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan;
  • Tatsuo Kakimoto
    Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan;

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説明

<jats:p> The roots and stems of dicotyledonous plants thicken by the cell proliferation in the cambium. Cambial proliferation changes in response to environmental factors; however, the molecular mechanisms that regulate cambial activity are largely unknown. The quadruple <jats:italic>Arabidopsis thaliana</jats:italic> mutant <jats:italic>atipt1;3;5;7</jats:italic> , in which 4 genes encoding cytokinin biosynthetic isopentenyltransferases are disrupted by T-DNA insertion, was unable to form cambium and showed reduced thickening of the root and stem. The <jats:italic>atipt3</jats:italic> single mutant, which has moderately decreased levels of cytokinins, exhibited decreased root thickening without any other recognizable morphological changes. Addition of exogenously supplied cytokinins to <jats:italic>atipt1;3;5;7</jats:italic> reactivated the cambium in a dose-dependent manner. When an <jats:italic>atipt1;3;5;7</jats:italic> shoot scion was grafted onto WT root stock, both the root and shoot grew normally and <jats:italic>trans</jats:italic> -zeatin-type ( <jats:italic>t</jats:italic> Z-type) cytokinins in the shoot were restored to WT levels, but isopentenyladenine-type cytokinins in the shoot remained unchanged. Conversely, when a WT shoot was grafted onto an <jats:italic>atipt1;3;5;7</jats:italic> root, both the root and shoot grew normally and isopentenyladenine-type cytokinins in the root were restored to WT levels, but <jats:italic>t</jats:italic> Z-type cytokinins were only partially restored. Collectively, it can be concluded that cytokinins are important regulators of cambium development and that production of cytokinins in either the root or shoot is sufficient for normal development of both the root and shoot. </jats:p>

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