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