auksin 2015

Dwi Setyati 2015

• Hormones– Auxins

– Cytokinins

– Gibberellins (GA)

– Ethylene (ethene)

– Abscisic acid (ABA)

• Other growth regulators– Brassinosteroids

– Salicylic acid (SA)

– Jasmonic acid (JA)

– Systemin

Canary grass coleoptiles

Under normal conditions, shoot tips bend towards the light

Without light on the tip, no bending

When not at tip, collar doesn’t

prevent bending

Conclusion: Light is sensed at the tip, but response not at tip

New hypothesis: A substance or chemical is transported

Auxin later isolated from shoot tips and established to be involved in cell elongation

•Isolasi auxin dari tumbuhan tinggi diperoleh pada th 1946determinasi dg Mass spectrometry pd th 1972 menggunakan 15.000 potongan ujung koleoptil tanaman jagung

•Dalam tubuh tumbuhan dijumpai dlm bentuk :bebas (IAA)terikat dg molekul lainsebagai prekursor : indol asetaldehid, indol asetonitril,

indol etanol, triptamin

Auxin role:

http://www.youtube.com/watch?v=zctM_TWg5Ik

Plant Hormone: Auxin

ALL Pea

Mustard and Corn

IAA IBA (indol asam butirat) PAA (phenil asam asetat) 4-Cl-IAA (found in pea, more active than

IAA)*promote pea pod development*increase the expression of PsGA3ox1 mRNA inpea pod

Naturally occuring Auxin

IBA (indol asam butirat)◦ Banyak digunakan untuk memacu perakaran◦ More stable than IAA against in vivo catabolism and

inactivation by conjugation◦ Plants are able to convert IBA to IAA and vice versa

Masih belum jelas apakah IBA = IAA ?

IBA = prekursor IAA?

◦ PAA: more abundance but has a low auxin activity10- to 100-fold lower than IAA and IBAdijumpai hanya pada lokasi tertentu

Naturally occuring Auxin

berikatan dengan gugus ester:6-O-IAgluc, IAA-Inos, IAA-glycoproteins

Berikatan dengan gugus amida:IAA-aminoacidIAA-proteinsIAA-peptides

Auksin konjugate

Jalur biosintesis auksin:◦ 1. Jalur indol asam piruvat

◦ 2. Jalur triptamine◦ 3. Jalur indol acetaldoxime

Biosintesis auksin

Jalur sintesis: IPA Triptofan Triptofan

transaminasi dekarboksilasi

indol asam piruvat Triptamin

dekarboksilasi oksidasi

indol 3-asetaldehid indol 3-asetaldehid

oksidasi oksidasi

Indol-3-Acetic Acid Indol-3-Acetic Acid

*Jalur triptamin dijumpai pada tanaman tembakau, gandum, tomat, barley

http://users.ugent.be/~pdebergh/pri/pri4et04.htm

Biosynthesis, Perombakan/inactivation other auxins Hidrolisis IAA & IAA konjugate Transport, Kompartmentasi (kadar di dalam sel)

Auksin metabolisme

Metabolisme Auksin

Ada tiga macam mekanisme yang mengatur :

1. Oksidasi oleh cahaya (foto oksidasi)chy

IAA → → indol asam karboksilat, indol asam glikolat (in aktif)

2. Oksidasi oleh enzimIAA oks / Peroksidase

IAA → → → → → → → → → metilen oksindol

3. Terikat oleh molekul organik sehingga inaktifBerikatan dengan gugus amida:IAA-aminoacidIAA-proteinsIAA-peptidesBerikatan dengan gugus ester :6-O-IAgluc, IAA-Inos, IAA-glycoproteinsIAA + As. Aspartat → → indol asetil aspartat (tidak aktif).

Site of synthesis & transport

*Jaringan meristematik, bagian-bagian yang sedang tumbuh

•Transport : polar, terutama melalui sel-sel parenkim yang berhubungan dengan berkas pengangkut

Auxin is the only plant hormone known to be transported polarly.

Polar transport is basipetal (toward the base).

Transport Active

Movement of auxin through certain plants is polar◦ unidirectional from apex to

base, but not due to gravity

◦ Transport depends on location of auxin anion efflux carriers,membrane proteins that are confined to basal ends of cells

◦ In cytoplasm at neutral pH, auxins have negative charge (anions)

◦ Proton pumps in plasma membrane pump H+ out, making cell walls acidic

◦ As anions, auxins can only leave cell at base by efflux carriers

Figure 37.9 Polar Transport of Auxin

10-11 10-9 10-7 10-5 10-3 10-1

Molar concentration of IAA

promotion

inhibition

akar

batang

Sensitivitas jaringan tumbuhan terhadap IAA

Efek Fisiologis Auksin

abscission - loss of leaves

flower initiation

sex determination

fruit development

apical dominance

Cell Enlargement Shoot Growth Internodes Tubers Bulbs Root Growth Storage Roots Adventicious Roots Fruit Growth Strawberry - Receptacle enlargement Apical Dominance Auxin:Cytokinin Ratio High - Dormant Axillary Buds Low - Axillary Bud Growth

Rooting of CuttingsPropagationGreenhouse and Nursery Crops

Hormodin, Rootone, etc.Commercial preps of 2,4-D

Herbicide High Concentration 2,4-D Dicots more sensitive Monocots less sensitive Weed control in cereal crop production Prevent Abscission of Leaves and Fruit Older leaves Ripe Fruit Endogenous production of IAA stops Replaced by exogenous NAA

Fototropism

Tropism- directional growth in response to an external stimulus.

Plants in a window usually bend toward the light. You may wonder how the plant is attracted to the light Tropisms are controlled by a plant hormone called auxin Auxin is produced at the growing tips of plants. .

When light strikes coleoptile on one side auxin moves laterally to other side

cell growth increases on that side

Seedling bends toward light

◦ If a shoot is tipped over, even in dark, auxin will move to the lower side cell growth results in bending of shoot so that it grows

up — gravitropism.

Upward gravitropic response of shoots is negative gravitropism; downward response of roots is positive gravitropism

The amount of auxin in the cells controls the amount of cell elongation. Experiments show that auxin is

sensitive to light. As a result, auxin concentrations are always higher on the shaded side of a stem.

Geotropism (gravitropism) – growth directed by gravity

Fenomena penghambatan terhadap tumbuhnya tunas lateral oleh tunas pucuk disebut sebagai dominasi apikal.

• Auksin yang disintesis di pucuk batang yang bertanggung jawab terhadap penghambatan pertumbuhan tunas lateral.

One week

Auxin production & transport from tip inhibits lateral bud growth

Pinching the tip releases buds for growth

The actual mechanism is not simplistic: IAA may induce ethylene production which inhibits lateral bud growth. Cytokinins which move apically may actually be of greater importance.

Control

Two weeks

http://koning.ecsu.ctstateu.edu/apical/apical.html

•Apical dominance is thought to be caused by the apical bud producing IAA (auxin) in abundance. This auxin is transported basipetally from the apical bud. The auxin causes the lateral buds to remain dormant. How could a lower concentration cause lateral buds to remain dormant and a higher concentration cause the apical bud to grow? This is explained in the following graph:

Apical Dominance

drop in auxin concentration (see

graph). Thus, decapitating (pruning) a

shoot will cause it to branch!

When the apical bud is

removed, the source of IAA is

removed. Since the auxin

concentration is much lower, the

lateral buds can now grow. In

fact their growth will be

stimulated by a relativley small

High auxin concentration

Low auxin concentration

Drawings depicting Coleus (Lamiaceae family)

Abscission – detachment of old leaves from stem◦ Auxin inhibits abscission,

which results from breakdown of cells in abscission zone of petiole

◦ Timing of leaf fall is determined in part by decrease in movement of auxin from blade through petiole

Figure 37.11 Changes Occur when a Leaf Is About to Fall

Shorter days of fall, drought, or the lack of nutrients cause lower auxin production

A "senescence factor" stimulates cells to form ethylene which produces cellulase (an enzyme that breaks down cellulose) and pectinase.

Middle lamella is digested causing cells to separate causing abscission.

Ratio of auxin to cytokinin may play a role

When a gardener takes cuttings from a plant, the base of each

cutting is first dipped into a rooting compound to stimulate

the growth of roots.

Many rooting compounds contain auxin.

Applications of plant hormones

www.beauchamp.leics.sch.uk/ast/resource/tctc/Student%20Resources/Powerpoints/tropism.ppt

• The inferior part of the plant including roots ( or root cap) is cut off and the plant is put in a medium containing auxin or free of it.

• Without auxin, adventitious roots can developed. This is the principle of cuttings.

• However, with auxin, root development is much better.

stimulate adventitious root

With synthetic auxin Without synthetic auxin

Saintpaulia (Gesneriaceae family)Another example of misleading common name

The African violet is not in the violet family

Adventitious roots growing from stem tissue

Fruit development normally depends on fertilization of the egg◦ If unfertilized ovaries are treated with auxin

or gibberellins, fruit will form —parthenocarpy

◦ Some plants spontaneously form parthenocarpic fruits (e.g., grapes, bananas, some cucumbers).

Parthenocarpic fruit- by treating a female flower parts (carpels) of certain species with auxin it is possible to produce a fruit (without fertilization- a virgin fruit) i.e. seedless tomatoes, cucumbers and eggplants.

Developing seed is a source of auxin

Auxins can be sprayed onto flowers so that the fruits develop without

pollination or fertilisation.

These fruits are seedless.

PROCESS: PARTHENOCARPY

Applications of plant hormones

www.beauchamp.leics.sch.uk/ast/resource/tctc/Student%20Resources/Powerpoints/tropism.ppt

Fragaria (Rosaceae family)

Band of achenes removed

What do you expect?

Not shown: Auxin replacement restores normal fruit formation and can be used commercially to produce seedless fruits

All achenes removed

Normal conditions

Without seed formation, fruits do not develop. Developing seeds are a source of auxin.

However, too much auxin can kill the plant and thus synthetic auxins used commercially as herbicides

Applications of plant hormones

Weeds have broader leaves than the grass on a lawn. The weeds will take up more auxin than the grass when

the lawn is sprayed.

Can you explain the use of hormones in each diagram.

Click to reveal the answer.

Auxins can be used as herbicides.

The weeds will grow too quickly and die.

www.beauchamp.leics.sch.uk/ast/resource/tctc/Student%20Resources/Powerpoints/tropism.ppt

Auxin- sintetik

• indolebutyric acid (IBA)

• 2, 4 dichlorophenoxyacetic acid (2,4D)

• 2, 4, 5 trichlorophenoxyacetic acid (2, 4, 5 T)

• picloram

Growth Regulator Herbicides

These herbicides affect several plant processes such as :

*cell division, cell enlargement,

*protein synthesis and respiration.

They act by upsetting the normal hormonal balance in plants.

Karakteristik

Umumnya diaplikasikan lewat daun, tetapi bisa meninggalkan residu di tanah

Length of soil activity tergantung konsentrasi yang diaplikasikan

Highly translocated in susceptible plants (systemic)

Aktifitasnya sebagai herbisida bervariasi untuk masing-masing spesies

Primarily broadleaf activity but can affect grasses

Gejala yang timbul akibat herbisida

Tanaman berdaun lebar tumbuh memutar

(twisting) dan melengkung (curling)

Untuk rumput-rumputan dapat menunjukkan daun

yang menggulung (leaf rolling), pertumbuhan akar

yang abnormal, serta mengakibatkan sterilitas

bunga dan bulir yang tak berisi.

Digunakan sebagaiherbisida

A mixture of 2,4,-D and 2,4,5-T was the "agent orange" used by the U.S. military to defoliate the forest in parts of South Vietnam.

PEMANJANGAN SEL

Figure 37.13 Cellulose in the Cell Wall

Auksin menginisiasi pemanjangan sel dengan cara mempengaruhi pengendoran /pelenturan dinding sel.

Bagaimana dinding sel menjadi lebih LUNAK/LENTUR di bawah pengaruh auksin? ADANYA perubahan sifat fisik dari dinding sel, yaitu :

1. elastisitas yang berkaitan dengan kemampuan peregangan yang dapat balik (reversible)

2. plastisitas yang tidak dapat balik (irreversible).

Auksin memacu protein tertentu yang ada di membran plasma sel tumbuhan → menginduksi POMPA PROTON untuk memompa ion H+ ke dinding sel (pH sitoplasma netral → di dinding sel pH menurun/ asam). Keasaman dinding sel

meningkatkan elastisitasnya

ELASTISITAS

IAA stimulates H+ pumps in the cell membrane.

H+ pumps secrete H+ into the cell wall, decreasing its pH.

This acidifies the cell wall which activates pH-dependent enzymes and breaks bonds between cellulose microfibrils.

The wall "loosens" because of the broken bonds and the turgor pressure expands the cell.

Acidified cell walls have increased elasticity

•Ion H+ ini mengaktifkan enzim tertentu sehingga memutuskan beberapa ikatan silang hidrogen rantai molekul selulosa penyusun dinding sel/ putusnya ikatan kimia antara mikrofibril dengan matrik dinding sel•pelarutan material dinding sel oleh enzim hidrolisis.

orientasi mikrofibril dibawah tegangan berubah

PLASTISITAS

Orientation of cellulose microfibrils determines direction of cell expansion

◦ For cells to expand, wall must loosen and stretch, and new polysaccharides and cellulose microfibrils deposited

◦ Plant cell walls recover incompletely from being stretched.

◦ Reversible stretching is elasticity; irreversible stretching is plasticity