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Mori, H. Nagoya University

Apical Dominance is controlled by Interaction between Cytokinin biosynthesis/degradation and Auxin in Stem. Mori, H. Nagoya University. 3days after decapitation. intact. Apical Dominance. outgrowth. cytokinin. auxin. axillary bud. dormant. decapitation. PCNA. CycD3. ;1. cdc2.

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Mori, H. Nagoya University

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  1. Apical Dominance is controlled by Interaction between Cytokinin biosynthesis/degradation and Auxin in Stem. Mori, H. Nagoya University

  2. 3days after decapitation intact

  3. Apical Dominance outgrowth cytokinin auxin axillary bud dormant decapitation

  4. PCNA CycD3 ;1 cdc2 histoneH4 CycB1 ;2 EtBr 0 2 4 6 8 10 12 14 16 18 20 22 24 Time after decapitation (hours) Northern Blot Analyses of Cell Cycle Related Genes

  5. 2cm 6cm 4cm 1cm

  6. Expresson of PCNA mRNA

  7. auxin axillary bud dormant decapitation outgrowth cytokinin ・Auxin derived from terminal bud is transported basipetally. ・When auxin applied to the cut stump after decapitation, Auxin can repress axillary bud outgrowth. ・When auxin directly applied to axillary bud after decapitation, Auxin cannot repress axillary bud outgrowth.

  8. Auxin is basipetallytransported in stem. IAA axillary bud Scale leaf at 2nd node

  9. The basipetal transport of auxin is essential for dormancy of axillary bud. Auxin acts at node or in stem, not in axillary bud.

  10. The basipetal transport of IAA is essentialfor axillary buds dormancy IAA 3 hr intact decapitated IAA 1cm 0 hr 1 hr auxin transport rate: 1cm/hr

  11. Subtracted cDNA clones 0hr-3hr Ps-IAA4/5, IAA7, Aux28, Aux22, GH3, F-box, cullin, auxin efflux carrier protein(PIN1 ), RD29B, LEA4, zeaxanthin epoxidase 3hr-0hr IAA-Ala hydrolase, GA2 oxidase, HMG-CoA synthase, squalene synthase, Isopentenyltransferase (IPT )

  12. Current model of cytokinin metabolism in higher plants LOG LOG LOG LOG (revised)

  13. 1cm 2nd node

  14. Expression of PsIPTs at the 2nd Node after Decapitation PsIPT1 PsIPT2 rRNA 0 0.5 1 2 3 4 5 6 9 12 15 18 24 time after decapitation (hr)

  15. excise the segments 3hr after decapitation IPT is expressed 1cm incubate in MES buffer with or without IAA Is IPT expression repressed? incubate in MES buffer with or without IAA excise the segments from intact seedlings Is IPT expressed? IPT is NOT expressed

  16. PsIPTs Expression was Repressed by IAA 10-5 M IAA IAA Free PsIPT1 PsIPT2 rRNA 0 1 2 3 4 5 0 1 2 3 4 5 incubation time (hr)

  17. excise the segments after 3hr decapitation IPT is expressed 1cm incubate in MES buffer with or without IAA Is IPT expression repressed? incubate in MES buffer with or without IAA excise the segments from intact seedlings Is IPT expressed? IPT is NOT expressed

  18. PsIPTs Expression was Induced in IAA Free Buffer 10-5 M IAA IAA Free PsIPT1 PsIPT2 rRNA 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 incubation time (hr) incubation time (hr)

  19. excise the segments after 3hr decapitation IPT is expressed 1cm 10-5 M IAA incubate in MES buffer with or without IAA Repress IPT expression? 0 1 2 3 4 5 incubate in MES buffer with or without IAA excise the segments from intact seedlings IPT express? Not IPT expression 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 IAA Free 0 1 2 3 4 5 IAA Free 10-5 M IAA

  20. PsIPTs Expression was Repressed by IAA Transported Basipetally in the Stem IAA Lanoline paste w or w/o IAA after decapitation ＋ PsIPT1 1cm 3hr PsIPT2 Is IPT expression repressed? PsPIN1

  21. pPsIPT2::GUS in Arabidopsis

  22. pPsIPT2::GUS (2,4-D treated for 1 week)

  23. pPsIPT2::GUS (2,4-D free for 3 days)

  24. IAA Free 10-5M IAA 0 0 1 1 2 2 3 3 4 4 5 5 incubation time (hr) GUS Transcripts Deceased by Auxin in Transformants harboring pPsIPT2::GUS

  25. Cytokinin Levels in the Stems and Axillary Buds after Decapitation

  26. Cytokinin Levels in the Excised Segments treated with/without IAA -IAA 0h 3h 300 300 6h 0h 3h 6h 200 200 100 100 0 0 iPMP iPA iP t-ZMP t-ZR t-zeatin iPMP iPA iP t-ZMP t-ZR t-zeatin +IAA (p mol/ gFW) (p mol/ gFW) ± 1%(w/v) IAA treatment excised the segments put on the agar plate

  27. Conclusion One role of auxin in apical dominance is to repress the PsIPTs expression; local cytokinin biosynthesis in the nodal stem is negatively regulated by auxin through the control of IPT expression. Cytokinin, which is thought to be derived from the roots so far, is locally biosynthesized in the stem rather than in the roots after decapitation.

  28. PsIPTs Expression was Repressed by Basipetally Transported IAA in the Stem IAA ＋ PsIPT1 1% (w/v) IAA after decapitation 1cm 3hr PsIPT2 Is IPT expression repressed? PsPIN1

  29. 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 1 2 4 3 Effect of IAA Applied to the Stump on PsPIN1 Expression PsPIN1 actin (cm) 0 1 2 4 (hours) IAA

  30. Can IAA from Axillary Buds induce PsPIN1? IAA Biosynthesis decapitated intact IAA IAA 3hr 9hr 0hr

  31. 4 8 10 12 0 2 4 6 8 10 12 0 2 6 IAA IAA × Lower Stem Upper Stem PsPIN1 actin Time after decapitation ( hours )

  32. Expression of PsIPTs at the 2nd Node after Decapitation PsIPT1 PsIPT2 rRNA 0 0.5 1 2 3 4 5 6 9 12 15 18 24 time after decapitation (hr)

  33. upper stem node lower stem (p mol/gFW)

  34. Cytokinin oxidase cDNAs were isolated from the stem 12 hr after decapitation. PsCKX1： was constantly expressed in stem before and after decapitation, was not induced by auxin. PsCKX2： was increased in stem after decapitation was induced by auxin.

  35. 120 80 decapitation Relative amounts of mRNA TIBA treatment 40 0 0 20 30 10 Expression of PsCKX2 in Pea Stem Time after treatment (hr)

  36. +NAA -NAA PsCKX2 Expression in Excised Pea stem by Auxin (x 103) 40 30 Relative amounts of mRNA 20 10 0 0 10 20 Time after treatment (hr)

  37. 120 80 40 - NAA 0 PsCKX2 Expression in Pea stem Relative amounts of mRNA 0 10 20 Time after treatment (hr)

  38. +NAA -NAA PsCKX2 Expression in Excised Pea stem by Auxin (x 103) 40 30 Relative amounts of mRNA 20 10 0 0 10 20 Time after treatment (hr)

  39. upper stem node lower stem (p mol/gFW)

  40. Expression of PsCKX2, PsPIN1, PsIPT2 in stem 120 PsCKX2 80 PsPIN1 Relative amounts of mRNA PsIPT2 40 0 0 10 20 30 Time after decapitation (hr)

  41. Model of Interaction Between Auxin and Cytokinin in Apical Dominance

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