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Hormones: Gibberellic acids (GA)
Bakanae: crazy seedling (rice)
Gibberella fujikuroi (GA3) rare in plants
Increased plant height
Reduced seed set and yield
Gibberellic acids
(GA) structures
Hormones: Gibberellic acids (GA)
Plant height regulators ……and more
Gregor and his
peas….. (1866)
GA1 is relevant for cell elongation
GA20 regulates germination
Gibberellic acids: effects on plants
Growth of inflorescence: elongation of internodes
Seed germination: induction of -amylaseBreaking dormancy
Gibberellic acids: effects on plants
Degradation of GA1 through GA 2-oxidase
35S GA 2-oxidase
Gibberellic acids: effects on plants
GA1 inhibitor AMO reverses GA effect
GA1 stimulates elongation in spinach
GA effects on plants
Fruit growth and ripening
GA effects on plants
Tuber formation
Short days: less GA1
Long days: more GA1
Auxin
Gibberellins
Auxin promotes GA biosynthesis (Synergy of phytohormones)
How does GA work?
Represses genes needed for growth
GA signal migrates into the nucleus and inactivates repressors RGA/GAI
GA signalingintermediate
Signaling protein
Hormones
Communication among cells, tissues and organs
Cytokinin:
What is it?
Where and how is it made?
What effect is due to cytokinin?
How does it work?
Cytokinin and tissue culture
Crop breeding and tissue culture selection
Together with auxin regeneration of callus tissue
IAA (mg/l)
Kinetin (mg/l)
0 0.005 0.20.03 1 3
0.01
0.2
1
Cytokinin effects:
Cytokinin biosynthesis in the root
also: young tissues, embryos, meristems
Transport through xylem to shoot and leaves
catabolized through cytokinin oxidase
Isopentenyl-adenine(basic cytokinine structure)
Cytokinin effects: senescence
Green island formation on fall leaves
Delay and reversal of senescence
Overproduction of cytokinin biosynthesis genes:delayed senescence
Cytokinin effects: pathogens
Witches broom: leafy galls on trees
Rhodococcus fascians Agrobacterium tumefasciens: crown gall
Identifying a receptor: cre1
wild-type
cre1
Identifying a receptor family:ahk2, ahk3, cre1
Cytokinin signal is transduced to its
response genes in the nucleus
Cytokinin signalCytoplasm
Signal transduction of cytokinin goes through protein kinases
Signal transduction through two-component signal transducers
Ethylene: it’s a gas!!
C C
H
H
H
H
Biologically active at less than 0.1ppm
Transported as ACC
Synthesized in ripening fruit and senescing tissues
Induced by auxin, draught, wounding, cold, stress,fruit ripening, senescence, pathogen attack
Ethylene: it’s a gas!!
Biologically active at less than 0.1ppm
Transported as ACC
Synthesized in ripening fruit and senescing tissues
Induced by auxin, draught, wounding, cold, stress,fruit ripening, senescence, pathogen attack
1864 illuminating gas powered street lights defoliate trees1901 Neljubov identifies ethylene as phytohormone1917 Doubt identifies ethylene as defoliant1934 ethylene biosynthesis in plants detected1935 ethylene is the “ripening hormone”
Auxin prevents abscission
However: unphysiological auxin concentrations have herbicide effects (agent orange)
Antisense-Inhibition of ACC-Oxidase stops flower senescence
Ethylene the defoliant….
…and fruit ripening hormone
Ethylene: triple response
Triple response:- thickening of hypocotyl, radial growth- eduction of cell elongation in hypocotyl and root- exaggerated curvature of apical hook, reduced geotropism
Understanding the hormone:
Searching for ethylene mutants
etr1
ctr1
Ethylene resistant
Constitutive tripleresponse
Air
Ethylene
Understanding the hormone:Searching for ethylene mutants
(ETO1)
Air
Ethylene
eto1
Ethylene overproducer
Wild-type
- Ethylene overproducer show same phenotype as ctr1
- ctr1 not reversible by inhibitors of ethylene biosynthesis
- eto phenotype is reversed by ethylene synthesis inhibitors
ETO1 has de-regulated ethylene biosynthesis
Understanding the hormone:Searching for ethylene mutants
(ETR1)
Ethylene resistant
Air Ethylene
Air Ethylene
Wild-typeEtr1
etr1 Etr (ethylene resistant)Ein (ethylene insensitive)
Ethylene receptors
Understanding the hormone:Searching for ethylene mutants
(CTR1)
ctr1
Constitutive tripleresponse
air
Wild-typectr1
air ethyleneethylene
Recessive loss-of-function ctr1 mutations:- Constitutive activation of ethylene response- Ethylene induced genes are always “on”- Constitutive triple response
CTR1 leads to inhibition of ethylene response in absense of ethylene
Genetic epistasis
Phenotype of first gene is masked by phenotype of a second gene
ETR1, EIN4, ETR2
EIN2, EIN3, EIN5
CTR1
etr1-3 ctr1-1ein4-1 ctr1-1etr2-1 ctr1-1ein2-1 ctr1-1ein3-1 ctr1-1ein5-1 ctr1-1
constitutive triple responseconstitutive triple responseconstitutive triple response ethylene insensitive ethylene insensitive ethylene insensitive