2细胞分裂素 Cytokinins

细胞分裂素类cytokinins.PPT,6.3 细胞分裂素类 cytokinins 6.3.1 发现 (Related to tussue culture) 1942年,Overbeek 发现椰子乳刺激曼 陀萝胚的生长,并刺激离...

细胞分裂素 Cytokinins

• Discovery of Cytokinins
  • 1950s
    • Folke Skoog’s research group identified a synthetic cytokinin, kinetin
  • Cytokinin was discovered through efforts to identify compounds that increase the growth of plant cells in culture.
• Types and Structure of Cytokinins
  • Major cytokinins
    • Cytokinins are N6-substituted adeninerelated compounds. Trans-zeatin and isopentenyl-adenine are the most active and abundant CKs
    • 类异戊二烯类CKs
    • 芳香环形式CKs
    • 结合态CKs
• Biosynthesis of cytokinins
  • Biosynthetic pathway of CK in Arabidopsis
    • iPMP-dependent
    • iPMP-independent
  • Production of active CKs
• Metabolism of cytokinins
  • Cytokinin can be inactivated by conjugation or degradation
    • The CKX genes are important regulators of active cytokinin levels
  • CKX overexpression enhances root growth and decreases shoot growth
• Transport of Cytokinins
  • Two non-specific cytokinin transport proteins have been identified
    • PUP preferentially moves the free base, and ENT moves the riboside, but neither is specific for CKs and their biological functions are not well characterized. ABCG14 moves iP- and tZtype CKs.
• Perception and signaling
  • Cytokinin signaling is mediated by a twocomponent-like system
  • The Arabidopsis cytokinin response pathway
    • Pathway
      • CKs are perceived by hybrid histidine kinases
        • CK binding initiates a phosphorelay that ultimately activates type-B ARR (Response Regulator) transcription factors
          • CK signaling is negatively regulated by type-A and type-C ARRs
    • Arabidopsis has three CK receptors, AHK2, 3 and 4
    • Arabidopsis CK receptors have partially redundant activities in vivo
    • Type A ARRs are negative regulators of CK signaling
• Physiological Function
  • Cytokinins contribute to developmental patterning and meristem functions
    • CK promotes cell division and stem cell fate at the shoot apical meristem
    • CK inhibits root meristem size and cell division and promotes cell differentiation at the root apical meristem
  • Cytokinin is required for normal growth of SAM
  • Cytokinin suppresses growth of roots
  • CKs regulate root vascular development
  • Regulation of leaf senescence by CKs
    • Plants that express IPTunder the regulation of a senescence-induced promoter (SAG) have significantly delayed leaf senescence
  • CKs contribute to nutrient uptake and allocation
  • CKs are necessary and (sometimes) sufficient for root nodule development