Plant Signaling and Plant Hormones

Plant Signaling and Plant
Hormones
Example of Plant Cell Signaling
Response to a stem breaking through the
ground for the first time
Light activates Phytochromes (light receptor
connected to a kinase)
cGMP activated
Opens gated channels for Ca++ in cell membrane
Enzymes are phosphorylated
Calcium binds to Calmodulin
Turn on transcription factors
Activated kinases and turns on transcription
factors
Make Photosynthesis enzymes
Make enzymes to make chlorophyll
Make enzymes to decrease auxin production so don’t keep elongating the stems
Apakah itu hormon?
Batasan hormon
• Respon tidak harus bersifat memacu
• Ion K+ dan Ca2+ dapat menimbulkan respon
penting bagi tumbuhan, apakah dikatakan
hormon?
• Sukrosa, apakah termasuk hormon?
• Konsentrasi sukrosa utk menimbulkan efek
sekitar 1-5mM, sedangkan hormon hanya
≤1µM
• Hormon adalah senyawa organik yang
disintesis salah satu bagian tumbuhan dan
dapat dipindahkan ke bagian lain, pada
konsentrasi sangat rendah mampu
menimbulkan respon fisiologis
Hormone Action
The same hormone can have different effects depending on location, concentration,
developmental stage or plant, etc.
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Effect Gene Expression
Effect Enzyme Activity
Change Membrane Properties
Open Gated Channels
Change Metabolism
Stimulate Cell Division
Affect the differentiation and development of
cells
General Action of Hormones
1. Bind to receptors
2. Receptors change shape in response to binding
3. 2nd messengers are activated which activate enzymes
OR
1. Directly activate or cause transcription of enzymes
(particulary kinases which phosphorylate other
enzymes)
2. Enzymes ultimately:
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Activate gene transcription
Activate transcription factors
Deactivate transcriptional repressors
Cause chemical reactions
Plant Hormones/Phytohormones
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Auxin
Gibberellin
Cytokinins
Absicis Acid
Ethylene
• Auksin berasal dari bahasa Yunani, yaitu
Auxein yang berarti ‘meningkatkan’
• Pertama kali digunakan oleh Frits Went (1926)
seorang mahasiswa pascasarjana di Belanda
• Hormon auksin dapat berupa asam
indolasetat (IAA), asam-4-kloroindolasetat (4kloroIAA), atau asam fenilasetat (PAA)
AUKSIN
Plant Hormones (internal signaling) Auxin
• Produced by apical meristems, young leaves, developing
seeds and fruit
• Moves through the parenchyma cells themselves – not
vascular tissue - Transported by chemiosmosis
• In low conc. – causes cells to elongate faster
– Stimulates pumps to pump H+ into cell wall, ↓pH activates enzymes
that break down cell wall – allows water flowing in to expand wall
– Phototropism – growing toward light – elongates cells on dark
side faster
• In high concentrations - induces ethylene gas which slows cell
growth
• Control apical dominance
• Controls stem elongation in developing shoots
• Kills dicots/not monocots = pesticide for corn or grass fields
• Causes fruit to grow – if spray on plants, fruit will develop
without seeds = seedless fruit
Discovery of Gibberellins
Activity of gibberellins acid
GA3 > GA1 > GA4 > GA2
Gibberellins
• Produced in roots and young leaves
• Elongation and cell division in stems and leaves
(activates enzymes that allow cellulose digesting
enzymes to penetrate the cell wall)
• Cause germination of seeds – water stimulates
release of gibberellins – stimulates production of
amylase to break down carbohydrates
• Important for pollen development, pollen tube
growth
• Works with auxin for fruit growth (spray to make
seedless grapes)
Discover of Cytokinins
• In 1955 Carlos Miller et al isolated a “cell-divisionstimulating factor” from yeast DNA.
• It was named as kinetin because of its amazing power to
stimulate cell division (cytokinesis) in the presence of an
auxin.
• In subsequent years, many other compounds promoting
cell division have been synthesized. Miller and his
associates (1956) have grouped all such compounds
including kinetin under a generic name kinin.
• D.S. Leetham (1963) of New Zealand proposed the term
cytokinins for such substances. This term is the most
acceptable one.
Cytokinins
• Produced by the roots, Moves through the xylem.
• Stimulates cell division in roots, embryos, fruits,
retards protein breakdown and prevents aging in
leaves and fruits (florists spray on cut flowers to keep
them fresh), stimulates seed germination.
• Works with auxin, relative concentrations control
growth and differentiation of plant parts
• Works opposite auxin to control height vs. bushiness
(more auxin – grow tall, more cytokinins – more
axillary buds – bushier)
Penemuan Asam Absisat
• Tahun 1963, Frederick T Addicott menemukan
senyawa yang menyebabkan gugurnya buah
kapas, senyawa tsb adl absisin I dan II
• Philip F Wareing menemukan senyawa yang
menyebabkan dormansi pada tumbuhan berkayu,
Acer pseudoplatanus, senyawa tsb dinamakan
dormin
• RFM Van Steveninck meneliti senyawa yg
mempercepat gugurnya bunga dan buah pada
Lupinus luteus
• Tahun 1967, nama asam abisisat disepakati
Abscisic Acid
• Readies the plant for winter – slow growth of
buds, inhibits growth
• Causes stomates to close in a wilting plant,
opens the K+ channels so K+ leaves guard
cells, water follows
• Keep seeds dormant when conditions not
suitable (light, rain, etc. inactivates abscisic
acid to cause seeds to germinate)
Penemuan Etilen
• Sudah sejak lama diketahui bahwa buah
menghasilkan suatu gas yang berperan pada
proses pematangannya
• Pada tahun 1934, R Gane membuktikan
bahwa gas etilen yg disintesis oleh tumbuhan
menyebabkan pemasakan buah tersebut
Ethylene
• Gas – causes fruit ripening (breakdown of starch to
sugar, breakdown of cell walls to soften, chlorophyll
breaks down)
• Inhibits axillary growth in response to high auxin
• Causes leaf death in winter (can’t get water from
frozen ground – don’t want to lose water from
leaves)
• Produced also in response to stress (drought, flood,
infection)
• Destroys inside of xylem to make hollow tubes
• Plant growth in sprouting plant – when hits
something solid – secretes ethylene – plant grows
horizontally to escape object then turns upward
again
Brassinosteriods
• Cells elongation and division in stem (like
auxin)
• Prevents leaves from falling off
• Promotes root growth at low conc. and stops
root growth at high concentrations
Circadian Rhythms
• Fluctuations based on a 24 hour cycle – not
due to environmental stimuli – based on some
internal time clock
• Devoid of environmental clues – it deviates
slightly from the 24 hour cycle (vary from 2127 hours)
External Signaling in Plants
Light, Gravity, Mechanical Stimuli
• Phototropism – growing toward sun (Auxin)
• Gravitropism – roots grow down, stems grow up (Auxin)
• Thigmotropism – change in growth due to mechanical stress
(vines grow straight until contact – wrap around due to
differential growth on opposite sides)
• Rapid Leaf Movements – loss of K+ causes water loss and
leaves to fold up
• Sleep movements – transport K+ from 1 side of leaf to
another – changing water flow
• Rubbing or touching a plant changes gene expression – can
make plants shorter by rubbing the stem a couple of times a
day
Plant response to light
• Two types of light receptors
– Blue light receivers
– Phytochromes – receive red light – photoreceptor
linked to a kinase
• Photoperiodism – control of flowering and
leaf growth by length of days
– Short Day/Long Night – flower when light is
shorter than a critical length (flower late summer)
– Long Day/Short Night – flower when light is longer
than a critical length (flower in spring)
– Controlled by phytochromes – bound to a light
absorbing molecule – light changes shape of
phytochrome which change cellular responses)
Plant Response to Stress
• Lack of Water
– activate abscisic acid = K+ leaves and so does water –
guard cells close
– Leaf growth inhibited due to lack of turgor pressure, so
less water lost
• Lack of Oxygen (from overwatering – reduces air in
soil)
– Some form air tubes in roots (ethylene causes cell death in
ground cells in roots forming tubes, or roots are out of soil)
• Too much salt (causes water deficit)
– Make internal solutes to deep water potential lower in
plant
• Heat (enzymes denature, water evaporates)
– Transpiration for evaporative cooling
– Make heat shock proteins – may help prevent
denaturation of proteins
Plant Response to Stress Continued
• Cold
– Plants increase amt. of unsat. Fatty acids in membrane to make them
more fluid
– Change solute concentration in cells to prevent cooling with out ice
crystals forming in cells
• Herbivores
– Physical defenses – thorns, stickers
– Chemical toxins (ex. Make a weird aa that when incorporated into
insect proteins – proteins are misshapen and the insects die) (ex. 2 –
plant sends chemical signal in response to damage – signal causes
wasps to come and inject eggs into catepillars eating the plant, wasp
babies eat their way out)
• Infections
– Tough epidermis
– Phytoalexins and PR proteins – kill bacteria by dissolving their cell
walls
– Express defense genes – apoptosis of infected cells, produce
antibiotics
– Produce Salicylic Acid – makes cells resistant to attack