Mori, H. Nagoya University
description
Transcript of 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
auxin
axillary buddormant
decapitation
Apical Dominance
cytokinin
outgrowth
G2 check point replication cell size environment
G1 check point cell size environment
Quiescence (G0)Terminal Differentiation
CellCycle
S
G2
M
G1
cyclinD1, 2
cyclinD3
PCNA cyclinB
histoneH4
G1 S G2 M
cdc2
mR
NA
cdc2
CycD3;1
CycB1 ;2
histoneH4
PCNA
0 2 4 86 10 12 14 16 18 20 22 24Time after decapitation (hours)
EtBr
Northern Blot Analyses of Cell Cycle Related Genes
1cm 2cm4cm
6cm
Time after decapitation (hr)
0 2 4 6
Rela
tive A
cit
ivit
y
0
1 cm
2 cm
4 cm
6 cm
2000
Expresson of PCNA mRNA
axillary buddormant decapitation
auxin
cytokinin
outgrowth
・ 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.
Auxin is basipetally transported in stem.
IAAaxillary bud
Scale leaf at 2nd node
The basipetal transport of auxin is essential for dormancy of axillary bud.
Auxin acts at node or in stem, not in axillary bud.
The basipetal transport of IAA is essentialfor axillary buds dormancy
intact
IAA
0 hr
decapitated
IAA
1cm
1 hr 3 hr
auxin transport rate: 1cm/hr
Subtracted cDNA clones
0hr-3hr
3hr-0hr
Ps-IAA4/5, IAA7, Aux28, Aux22, GH3, F-box, cullin, auxin efflux carrier protein(PIN1 ),RD29B, LEA4, zeaxanthin epoxidase
IAA-Ala hydrolase, GA2 oxidase,HMG-CoA synthase, squalene synthase,Isopentenyltransferase (IPT )
Current model of cytokinin metabolism in higher plants
LOG
(revised)
LOG LOG LOG
1cm2nd node
0.5 4321 5 6 9 15 18 24120
PsIPT1
PsIPT2
rRNA
time after decapitation (hr)
Expression of PsIPTs at the 2nd Node after Decapitation
excise the segmentsfrom intact seedlingsIPT is NOT expressed
incubate in MES bufferwith or without IAA
Is IPT expressed?
excise the segments3hr after decapitation
IPT is expressed
incubate in MES bufferwith or without IAA
Is IPT expression repressed ?
1cm
1 2 3 4 50
IAA Free
1 2 3 4 50
10-5 M IAA
PsIPT1
PsIPT2
rRNA
incubation time (hr)
PsIPTs Expression was Repressed by IAA
excise the segmentsfrom intact seedlingsIPT is NOT expressed
incubate in MES bufferwith or without IAA
Is IPT expressed?
excise the segmentsafter 3hr decapitation
IPT is expressed
incubate in MES bufferwith or without IAA
Is IPT expression repressed?
1cm
PsIPTs Expression was Induced in IAA Free Buffer
IAA Free 10-5 M IAA
0 1 65432
incubation time (hr)incubation time (hr)
0 1 65432 987
PsIPT1
PsIPT2
rRNA
excise the segmentsfrom intact seedlingsNot IPT expression
incubate in MES bufferwith or without IAA
IPT express?
excise the segmentsafter 3hr decapitation
IPT is expressed
incubate in MES bufferwith or without IAA
Repress IPT expression?
1cm
1 2 3 4 50
IAA Free
1 2 3 4 50
10-5 M IAA
IAA Free 10-5 M IAA
0 1 654320 1 65432 987
PsIPTs Expression was Repressed by IAA Transported Basipetally in the Stem
PsIPT1
PsIPT2
PsPIN1
+IAA
Lanoline paste w or w/o IAA after decapitation
3hr
Is IPT expression repressed?
1cm
pPsIPT2::GUS in Arabidopsis
pPsIPT2::GUS (2,4-D treated for 1 week)
pPsIPT2::GUS (2,4-D free for 3 days)
IAA Free 10-5M IAA
10 2 3 4 5 10 2 3 4 5
incubation time (hr)
GUS Transcripts Deceased by Auxinin Transformants harboring pPsIPT2::GUS
Cytokinin Levels in the Stems and Axillary Buds after Decapitation
Cytokinin Levels in the Excised Segments treated with/without IAA
0
100
200
300
iPMP iPA iP t-ZMP t-ZR t-zeatin
0h3h6h
-IAA
(p m
ol/
gF
W)
0
100
200
300
iPMP iPA iP t-ZMP t-ZR t-zeatin
0h3h6h
(p m
ol/
gF
W)
+IAA
excised the segmentsput on the agar plate
± 1%(w/v) IAA treatment
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.
PsIPTs Expression was Repressed by Basipetally Transported IAA in the Stem
PsIPT1
PsIPT2
PsPIN1
+IAA
1% (w/v) IAAafter decapitation
3hr
Is IPT expression repressed?
1cm
Effect of IAA Applied to the Stump on PsPIN1 Expression
PsPIN1
actin
0 1 2 (hours)4
(cm)1 2 3 4 1 2 3 4 1 2 3 41 2 3 4
1 2 3 4IAA
Can IAA from Axillary Buds induce PsPIN1?
intact
0hr 9hr
decapitated
3hr
IAA
IAA
IAA Biosynthesis
Time after decapitation ( hours )
PsPIN1
actin
0 2 4 6 8 10 12 0 2 4 6 8 10 12
IAA
×
Upper Stem
IAA
Lower Stem
0.5 4321 5 6 9 15 18 24120
PsIPT1
PsIPT2
rRNA
time after decapitation (hr)
Expression of PsIPTs at the 2nd Node after Decapitation
IAA
81.7CK
2.9
IAA
44.0CK
9.1
IAA
19.3CK
135.5
IAA 20.8
CK105.
5
IAA
60.5CK
3.6
IAA
35.4CK
175.2
IAA175.
3CK
47.6
IAA
79.5CK
1.9
IAA
50.5CK
6.3
IAA
27.7CK
76.6
IAA
33.6CK
158.0
IAA
34.6
CK
94.8
IAA
39.9CK
50.7
IAA
55.2
CK
23.8
IAA 72.2
CK 7.8
0 1 3 12 18 24 36 48
(p mol/gFW)
node
upperstem
lowerstem
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.
Cytokinin oxidase cDNAs were isolated from the stem 12 hr after decapitation.
Time after treatment (hr)0 10 20 300
40
80
120
decapitation
TIBA treatment
Rel
ativ
e am
ou
nts
of
mR
NA
Expression of PsCKX2 in Pea Stem
Time after treatment (hr)0 10 20
0
10
30
40
(x 103)
20
Rel
ativ
e am
ou
nts
of
mR
NA
+NAA
-NAA
PsCKX2 Expression in Excised Pea stem by Auxin
Time after treatment (hr)0 10 20
- NAA40
0
80
120
PsCKX2 Expression in Pea stem
Rel
ativ
e am
ou
nts
of
mR
NA
Time after treatment (hr)0 10 20
0
10
30
40
(x 103)
20
Rel
ativ
e am
ou
nts
of
mR
NA
+NAA
-NAA
PsCKX2 Expression in Excised Pea stem by Auxin
IAA
81.7CK
2.9
IAA
44.0CK
9.1
IAA
19.3CK
135.5
IAA 20.8
CK105.
5
IAA
60.5CK
3.6
IAA
35.4CK
175.2
IAA175.
3CK
47.6
IAA
79.5CK
1.9
IAA
50.5CK
6.3
IAA
27.7CK
76.6
IAA
33.6CK
158.0
IAA
34.6
CK
94.8
IAA
39.9CK
50.7
IAA
55.2
CK
23.8
IAA 72.2
CK 7.8
0 1 3 12 18 24 36 48
(p mol/gFW)
node
upperstem
lowerstem
Time after decapitation (hr)
0 10 20 300
40
80
120
PsCKX2
PsPIN1
PsIPT2
Rel
ativ
e am
ou
nts
of
mR
NA
Expression of PsCKX2, PsPIN1, PsIPT2 in stem
Model of Interaction Between Auxin and Cytokinin in Apical Dominance
Effect of Striolactone GR24 on outgrowth of axillary bud after decapitation
GR24 control
Apical dominance
Nagoya University
・ Mina TANAKA
・ Sae SATO-SHIMIZU
・ Aiko ISHIWATA
・ Yuka MADOKA
RIKEN
・ Mikiko KOJIMA
・ Hitoshi SAKAKIBARA