plant hormones 2

04/13/23 BIOL1043/BIOL2051 Plant Science 1

PLANT HORMONES 2ABSCISIC ACID & ETHYLENE

Nitin Mantri

Biotechnology & Environmental Biology

School of Applied Sciences, RMIT University

Room 223.1.28

Tel. 03 9925 7152

Email: [email protected]


PLANT HORMONES 2ABA & ETHYLENE

auxins 1880 Darwin ethylene 1924/70 Osbornegibberellins (GA) 1926 Kurosawa/Brienabscisic acid (ABA) 1965 Wareing/Aldicottcytokinins 1956 Skoog, Miller‘florigen’?/phytochrome 1940s


ABSCISIC ACID (ABA) -HISTORY OF DISCOVERY

1965 ‘2 compounds’ discovered simultaneously

dormin (Wareing, UK) induction and maintenance of dormancy in

winter buds of deciduous trees

abscisin (Aldicott, USA) abscission of cotton fruits


ABSCISIC ACID (ABA) -HISTORY OF DISCOVERY

shown to be same compoundnow called abscisic acid (ABA)

but not hormone that induces abscission (ethylene)

accelerates abscission induces senescence and dormancy


STRUCTURE OF ABA

single molecule, although isomers possible (cis and trans)


MOLECULAR ACTIVITYProduction

organs under stress, e.g. water stress

Transport xylem and phloem (more abundant) bi-directional

Mechanism metabolised to dihydrophaseic acid at action

site, but active form unknown


PHYSIOLOGICAL ACTIVITIES 1. Dormancy

Leaf/flower bud

dormancy: dormant

organs have high levels

of ABASeed dormancy: accumulated ABA prevents seed

germination (example, grasses) adding high levels of ABA externally induces

dormancy can replace cold/short-day requirements in buds and

seeds


PHYSIOLOGICAL ACTIVITIES 2. Abscission

ethylene induces abscissionABA accelerates it

e.g. old leaves• auxin not exported

• forms ethylene instead

• induces abscission zone

• ABA accelerates abscission zone growth


PHYSIOLOGICAL ACTIVITIES 3. Senescencesenescent organs contain high levels of

ABAadding high levels of ABA induces

senescence chlorosis, necrosis e.g. leaves, fruit (most plants)

action of ABA depends on concentrations of other hormones


PHYSIOLOGICAL ACTIVITIES4. Flowering in short-day plants

unique propertycomplementary to GA

e.g. Phaseolus spp.


PHYSIOLOGICAL ACTIVITIES5. Stomatal closure

unique propertyin water-stressed leavesABA concentration in guard cells increasesK+ pump stopsloss of K+ from guard cellsloss of turgor -> stomata close


PHYSIOLOGICAL ACTIVITIES6. Enzyme effects

antagonises several effects of GA e.g.

amylases


PHYSIOLOGICAL ACTIVITIES7. Organ/tissue differentiation

in tissue cultures, size and deformities reduced in excised embryos

regulatory function


PHYSIOLOGICAL ACTIVITIES8. Interaction with GA

GA overcomes dormancy induced by ABA possibly from common precursor in tissue

mevalonic acid

good conditions poor conditions

GA ABA

growth dormancy

13/04/23 BIOL2156/2334 Plant Science 16

PLANT HORMONES 2ABA & ETHYLENE

Nitin Mantri

School of Applied Sciences

RMIT

Room 223.1.28

Tel. 03 9925 7152

Email: [email protected]


TYPES OF PLANT HORMONES

5 discovered and isolated for a long time auxins 1880 Darwin gibberellins (GA) 1926 Kurosawa/Brien cytokinins 1956 Skoog, Miller abscisic acid (ABA) 1965 Wareing/Aldicott ethylene

1924 fruit ripening 1970s general Osborne


ETHYLENE -HISTORY OF DISCOVERY 1901: Dimitry Neljubov – pea stems grew

horizontally 1924: used to promote fruit ripening, e.g. bananas fruit picked green->cold store->ripened

1970s: Daphne Osborne - most other properties discovered


STRUCTURE OF ETHYLENEH H

C====C

H H

normal levels in air 5-50 ppb (v/v) gas - plants stationery

good transport (diffusion) especially water plants, roots


MOLECULAR ACTIVITY

Production any wounded or senescent tissues produced on plasmalemma e.g. ripening fruits, senescing leaves

Transport – diffusion


MOLECULAR ACTIVITY Mechanism

growth• reorientation of microtubules• cells wider

ripening stimulation of degradative enzymes, e.g.

pectinases -> softening amylase (starch hydrolysis) -> sweetness organic acids -> esters (sweet/aromatic)

chlorophyll breakdown -> colour change


PHYSIOLOGICAL ACTIVITIES 1. Fruit ripening

fruit ripening by C2H4 -> climacteric

maxima in outputs of CO2 + C2H4

small amount of C2H4 released early stimulation of CO2 production

stimulation of C2H4 production

‘compound interest’ effect


PHYSIOLOGICAL ACTIVITIES 1. Fruit ripening


PHYSIOLOGICAL ACTIVITIES 1. Fruit ripening control of fruit ripening in storage

fruit picked unripe packed with KMnO4 (absorbs C2H4)

treated with C2H4 or chemicals that form C2H4 to ripen to order

now controlled atmosphere packaging used 95% nitrogen, 5% carbon dioxide


PHYSIOLOGICAL ACTIVITIES 1. Fruit ripening genetically engineered tomatoes lack key enzyme polygalacturonase for fruit softening


Ethylene Biosynthesis & Signalling

Steps and intermediates designated with an asterisk have been targeted for transgene modification in ripening fruit. EIN3, EILs, and EREBPs are localized in the nucleus. Jim Giovannoni Ann Review Pl Phy and Pl Mol Biol. 52, 725-749

Model for the Molecular Regulation of Tomato Fruit Ripening. Fruit harboring homozygous mutations for the indicated genes or loci are shown.

13/04/23 27Giovannoni J J Plant Cell 2004;16:S170-S180


INITIATION OF tEBR EXPRESSION IN FRUIT

mRNA quantified Different stages of

fruit ripening tEBR codes for

presumed receptor for ethylene

Breaker + 7 days = fully ripe


PHYSIOLOGICAL ACTIVITIES2. Abscission

C2H4 produced by senescing organs, e.g. leaves of deciduous trees petals of flowers after fertilisation

induction of abscission zone at base of organ, e.g. leaf, flower

acceleration of abscission by ABA


PHYSIOLOGICAL ACTIVITIES2. Abscission

flower senescence and abscission

ethylene synthesis pathway blocked

ACC oxidase gene anti-sensed

long-life carnations


2a. ETHYLENE MODEL


PHYSIOLOGICAL ACTIVITIES 3. Epinasty

drooping of foliage swelling of stem @ 1 ppm (v/v)

e.g. tomato Victorian parlour

plants (coal gas)


PHYSIOLOGICAL ACTIVITIES 4. Geotropism (diageotropism)

diageotropism horizontal growth negates +ve and –ve

geotropism


PHYSIOLOGICAL ACTIVITIES5. Seed germination

breakage of dormancy in some (large) seeds in high conc. C2H4

in soil, C2H4 produced by micro-organisms

high conc. C2H4 = safe to germinate



Prevention of photomorphogenesis

‘dark’ morphology in light-grown plants

etiolation lack of leaf expansion chlorosis (no greening)



Induction of flowering

Bromeliaceae only pineapple (Ananas) Tillandsia


PHYSIOLOGICAL ACTIVITIES7. Interaction with auxins

some effects - interaction of C2H4/auxins e.g. epinasty

other effects - C2H4 action unique unchanged by interaction with auxins

• e.g. flowering in bromeliads

• e.g. prevention of photomorphogenesis


ReferencesFurther reading (books) Attwell, B.J., Kriedemann, P.E., Turnbull,

C.G.N. (Eds). (1999). Plants in Action. Macmillan Education Australia Pty Ltd, South Yarra, Melbourne, Australia.

Bidwell, R.G.S. (1979). Plant Physiology, 2nd edn. Macmillan, New York, USA.

plant hormones 2

Science

biol1043biol2051 plant

biol21562334 plant science

abscission aba

types of plant hormones

aba ethylene auxins

accumulated aba

abscission zone aba

abscisic acid aba history