Venus Fly Trap + Plant Hormones Flashcards
What is the similarities between electric communication in plants and mammals?
Electrical communication in plants occurs only in certain plant species.
Similarities;
*Have electrochemical gradients
*Plant cells have sodium-potassium pumps
*Have resting potential
*Membrane depolarises ➡️ action potentials
What are the differences in electric communication between plants and mammals?
The depolarisation in mammals is due to Na+ enter, whereas in plants it’s due to Cl- move out
The action potential travels along neurons in mammals and in plants the action potential travels along cell membranes and cell-to-cell via plasmodesmata
The speed of transmission in mammals is faster and slower in plants.
Describe the structure of Venus fly trap
Mechanical energy is converted to electrical energy.
Nectar glands to attract insects
Stiff outer edges- interlock to trap insect inside
Lobe-specialised leaf
X6 sensory hairs-deflection stimulates action potentials and cause leaf to fold
Digestive glands-secrete digestive enzymes on lobes surface
Midrib-hinge
Describe how the Venus fly trap works
- Sensory hair cell is receptor and detect touch.
- if two hairs are touched/one hair is touched twice within 35 seconds…
*Ca2+ ion channels open @ cells at base of hair
*Ca2+ flow in
Cell membrane depolarised
➡️ action potential occurs
*Depolarisation spreads over leaf/lobe ➡️to midrib/hinge cells
- Acid growth @ hinge cells
*H+ pumped out of cells into cell walls
*Cross-links in cell wall broken
*Calcium pectate of middle lamella dissolves
*Cell wall loosens
*Ca2+ enter hinge cells
*Water enters hinge cells by osmosis
*Cells expand/ become turgid
*Lobes change from convexs to concave
*Traps shut quickly in 0.3s
*Elastic tension released
- Further deflections of sensory hairs
*Trigger action potentials➡️ seal trap
*Stimulate entry of Ca2+ into glands cells
*Ca2+ stimulate exocytosis of vesicles containing digestive enzymes
*Trap stays shut for up to 1w for digestion - After digestion, cells of upper surface of midrib grow slowly
*Leaf reopens and elastic tension builds in the cell walls of midrib
What adaptations do Venus fly traps have to conserve energy and to avoid closing unnecessary?
- Stimulation of single hair does not trigger closure
➡️At least two hairs must be touched OR one hair touched twice within 35 seconds
➡️Prevent trap from closing when raining or when debris fall into trap - Gaps between stiff hairs allow very small insects to crawl out
➡️No energy wasted on digesting a very small meal
Describe how chemical communication in plants occurs
Plant hormones/plant growth tissues
Produced in a variety of plant tissues
Not in endocrine glands
Plant hormones interact with receptors inside/outside cell and initiate a signaling cascade
How do plant hormones move?
A)Directly from cell to cell
➡️By active transport or diffusion
b) Via phloem/xylem vessels
e.g. Auxin,gibberellin, abscisic acid
What are the three plant hormones?
1.Auxins (IAA)
*Growth by cell elongation at tips of roots and shoots
*Inhibits lateral growth/ branching-I.e. apical dominance
*Via acid growth hypothesis
- Gibberellins (GA)
*Seed germination
*Stem elongation
*Causes breakdown of DELLA , which are inhibitors of cell growth and seed germination - Abscisic acid (ABA)
*Respond to water stress
*Stimulate closure of stomata
*Uses Ca2+ as second messenger
Describe Auxins
*Group of several chemicals
*Main auxin=IAA (indole 3-acetic acid)
Synthesized in growing tips of shoots and roots
➡️AKA apical meristems where there is active mitosis
Role of auxin:
1.Stimulate cell elongation
2. Inhibits lateral growth/branching -I.e. apical dominance
➡️Cause plants to grow taller towards light
O/s: Auxin not solely responsible for apical dominance
*There is interaction between auxin and other plant growth regulators
*Gibberellin enhances IAA
Uneven distribution of auxin can cause stem/ root to bend in respond to stimuli
➡️Higher concentration of auxin, more cell elongation
➡️E.g. auxin causes shoots to bend towards sunlight
*Auxin inhibits lateral growth at growing tips of shoots
➡️The act of pruning removes auxin
➡️Allows branching and produces bushier plants
Role of auxin in cell elongation
The acid growth hypothesis
- Auxin binds to receptors in cell surface membrane
2.Stimulates proton pumps in cell surface membrane
*By active transport
*H+ from cytoplasm into cell wall
*Cell wall becomes more acidic
- PH-dependent enzymes (expansions) activated to weaken cell wall
*By breaking H bonds between cellulose micro fibrils
*Cell wall loosens➡️more elastic, can stretch - Ions enter cell and water potential of cell decreases
*Water enter cell by osmosis
*Increase in turgor pressure
*Cell wall expands
^Cause elongation of cell
How is the acid growth hypothesis, of auxins role in cell elongation supported?
Hypothesis supported because…
1. Cell elongation can be prevented by neutralising the acidity of cell wall using buffer
2.Can cause elongation by acids
3. Protons released from cells in response to auxin
Describe gibberellins (GA)
- plant growth regulator/plant hormone
- synthesized in young leaves, seeds, and stems
*Roles:
1. Seed germination
2. Stimulates cell division and cell elongation in stem
P/S: There is interaction between gibberellin and other plant growth regulators
*Gibberellin enhances IAA
Describe the structure of seeds such as wheat and barley.
Pericap and testa- tough protective layer
Aleurone- protein rich layer
Endosperm-Storage of starch
Scutellum-Seed leaf
Embryo-Develops into new plant
What is the role of Gibberellin in seed germination?
*Seed is dormant/ metabolicy inactive
➡️DELLA proteins act as inhibitors of cell growth and seed germination
➡️Mantaina seed dormancy
- Seeds absorbs water by osmosis
➡️Water stimulates production of gibberellin by embryo - Gibberellin diffuses into cells of aleurone layer
*Causes breakdown of DELLA proteins
*Switches on gene coding for hydrolytic enzymes (e.g. amylase)
*Storage proteins in aleurone broken down into amino acids
➡️Stimulate synthesis of amylase
- Amylase diffuses into endosperm (tissue surrounding embryo)
*Hydrolyses starch to maltose in endocrine
*Maltose converted to glucose
Starch (amylase) ➡️ maltose (maltose ) ➡️ glucose
- Glucose diffusers into embryo plant
*Provides sources of energy for growth of embryo plant
Describe the role of in stem elongation
Control of gibberellin synthesis
*GA is plant growth regulator
*It stimulates cell division and cell elongation in stem
➡️Causes plant to grow tall
*Apply gibberellin to dwarf plants and they grow taller towards
➡️Dwarf plants have inactive form of gibberellin
➡️ 2 forms: active and inactive
1.dominant allele (Le)
*Codes for functional enzyme needed on gibberellin synthesis pathway
*Enzyme converts inactive to active gibberellin
*Plants with at least one dominant allele grow to normal height
- Recessive allele (le)
*Codes for non-functional enzyme needed
*Plants with 2 copies of the recessive allele cannot synthesise gibberellin
➡️develop into dwarf varieties
*Dwarf plants have inactive form of gibberellin
How does gibberellin work in its role in stem elongation?
Without GA:
*Transcription factor (I.e. PIF) attached to Della protein
*PIF cannot bind to DNA
When GA binds to receptor:
*Causes DELLA protein destruction
*Inhibition of transcription removed
*PIF binds to DNA
*PIF recruits RNA polymerase to bind to DNA
*Growth genes switched on
*Growth genes are switched on
1. Causes cell division in stem
2. Causes cell elongation in stem
*By interacting with auxin
*Loosens cell walls by acid growth hypothesis
*Uses expansions to break cross-links in cellulose cell wall
*So cells can expand when water enters
*Changes plasticity of cell wall
3. Increases internode length
Describe guard cells
*each stomatal pore is surrounded by 2 guard cells
*Sausage-shaped cells with chloroplasts
*Highly specialised cells
Characteristics:
a) unevenly thickened cell walls with ends of cells joined
➡️Wall adjacent to pore is very thick
➡️Wall furthest from pore is thin
➡️When turgid, thinner walls bend more readily than thicker walls
➡️Opens pore
B) bundles of cellulose micro fibrils arranged as hoops around the guard cells
➡️When turgid, cell increase in length and not diameter
➡️Cells will bend and curve when length increased
Describe the stoma opening mechanism
- Proton pumps in cell surface membrane of guard cells
*Pumps H+ ions out of the guard cells
*Low H+ concentration in guard cells
*Inside of cell more negative than outside
➡️Electrochemical gradient - This causes K+ channels open
*K+ enters via facilitated diffusion
*Cl- diffuse in
➡️Water potential of cell decreases - Water moves in by osmosis
*Via aquaporins - Volume of guard cells increase
*Become turgid and curve due to unequal thickness of cell wall ➡️ pore opens
Describe the stomatal response to the stoma opening mechanism.
Stomata opens in response to:
*Increase in light intensity
*Low CO2 concentration in air and spaces of leaf
➡️Gain CO2 for photosynthesis, allow O2 out
➡️Allow transpiration to occur ➡️ brings water and mineral ions in
Stoma closes in response to:
*decrease in light intensity
*High CO2 concentration in air spaces of leaf OR CO2 not required bcs no photosynthesis
*Low humidity/high temperature/high wind speed/water stress
➡️Maintain cell turgidity and prevent water loss by transpiration.
Describe Abscisic acid:
*Stress hormone
*Produced during water stress (e.g. very high temperature, reduced water supply)
*Synthesised in all cells with chloroplasts or amyloplasts (similar to chloroplasts but got large starch grains and no chlorophyll)
Role: Stimulate stomata closure
*Reduce water vapour loss from leaves (transpiration)
*Refucef rate of CO2 uptake for photosynthesis
*Fast response
*Do not regulate expression of genes
Describe the role of abscisic during water stress
- Abscisic acid is secreted and bind to abscisic acid receptors on the cell surface membrane of guard cells
- Abscisic acid stimulates Ca2+ influx
*From outside cell or inside vacuole into cytoplasm
*Ca2+ acts as a second messenger
*Triggers cascade of reactions - Calcium ions
*Inhibit proton pumps
➡️H+ cannot move out
➡️high H+ conc inside cell
*Inhibit K+ influx
*Promote K+ efflux (move out)
*Active channel proteins that allow -vely charged ions to leave the guard cells - Loss of ions increases water potential in guard cells
*Water leaves by osmosis
*Guard cells become flaccid
*Stomata close
*Response is very fast
