auksin 2015
DESCRIPTION
plant fisiologyTRANSCRIPT
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
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
