Plant Control Systems Flashcards
How do plants respond to stimuli?
Unlike animals which respond by movement, plants respond to stimuli by altering growth and development
Response in plants is carried out via signal transduction
signal transduction
Reception, transduction, response
how plants respond to stimuli
Etiolation
is the morphological adaptation required for growing in the dark
Give an example of etiolation and explain
Like a potato that sprouts in a dark cellular
Little light and no evaporative pressure in the leaves means the plant doesn’t need extensive roots right away
Plant focuses its energy on growing the stems, thus reducing the energy it takes for shoots to break ground
de-etiolation
When a plant shoot reaches light (“greening”) commences
What happens when de-etolation starts?
Stem elongation slows
Shoot beings to produce chlorophyll to initiate photosynthesis
What happens during reception?
- Light signal is detected by a phytochrome receptor located in the cytoplasm
- This activates at least 2 signal transduction pathways
What is the first pathway of transduction?
cGMP
What is the second pathway of transduction?
Ca2+ ions
What happens during the first pathway of transduction?
Weak levels of light trigger the phytochrome and initiates the secondary messenger cGMP through the activation of the enzyme guanylyl cyclase
• cGMP then activates a protein kinases, which carries the signal into a response
secondary messagers
A small, nonprotein, water-soluble molecule or ion, such as a calcium ion (Ca2+) or cyclic AMP, that relays a signal to a cell’s interior in response to a signalling molecule bound by a signal receptor protein.
What happens during the second pathway of transduction?
Second pathway Ca2+ ions Phytochrome activation opens up Ca2+ channels, flooding the cytosol with increase Ca2+ This activates a different protein kinase to initiate a response
What must happen for full de- etiolation to occur?
Both pathways must be induced for full de- etiolation to occur
Response
Both pathways lead to the expression of genes for proteins that function in the de- etiolation process
Products of response are enzymes for photosynthesis, chlorophyll production, plant hormones levels
What are the two main mechanisms by which a signalling pathway can enhance an enzymatic step in a biochemical pathway?
Post-transcriptional modification
Transcriptional Regulation
Post-transcriptional modification
modification of proteins
Pre-existing proteins are phosphorylated (phosphate added), altering protein shape and function (review Fig. 11.10)
Protein phosphatases dephosphorylate enzymes, turning off the signals
Transcriptional Regulation
Transcription factors bind to specific regions of DNA (see concept 18.2) to control transcription of genes on DNA
Activators=increase transcription
Repressors=decrease transcription
What are plant hormones?
(plant growth regulators)
• Signalling molecule produced in minute amounts in one part of the plant and transported to another part to initiate responses in cells and tissues
Each hormone can have a multitude of effects depending which tissue it is acting in, its concentration, and the developmental stage of the plant
Transported in the phloem sap
Where is Auxin (IAA) Produced
or Found in Plant?
shoot apical meristems and young leaves are the primary sites of auxin synthesis
Root apical meristems also produce auxin, although the root depends on the shoot for much of its auxin
Developing seeds and fruits contain high levels of auxin, but it is unclear whether it is newly synthesized or transported from maternal tissues.
Where is Cytokinins Produced or Found in Plant?
synthesized primarily in roots and transported to other organs
there are many minor sites of production as well
Where is Gibberellins (GA) Produced or Found in Plant?
Meristems of apical buds and roots, young leaves, and developing seeds
Where is Abscisic acid (ABA) Produced or Found in Plant?
all plant cells have the ability to synthesize abscisic acid,
found in every major organ and living tissue
may be transported in the phloem or xylem
Where is Ethylene Produced or Found in Plant?
a gaseous hormone produced by most parts of the plant
produced in high concentrations during senescence, leaf abscission, and the ripening of some types of fruits
Synthesis is also stimulated by wounding and stress.
Where are Brassinosteroids Produced or Found in Plant?
present in all plant tissues, although different intermediates predominate in different organs
Internally produced brassinosteroids act near the site of synthesis.
Where are Jasmonates Produced or Found in Plant?
a small group of related molecules derived from the fatty acid linolenic acid
are produced in several parts of the plant and travel in the phloem to other parts of the plant
Where are Strigolactones Produced or Found in Plant
carotenoid-derived hormones and extracellular signals are produced in roots in response to low phosphate conditions or high auxin flow from the shoot
What are the major functions of Auxin?
Stimulates stem elongation (low concentration only);
promotes the formation of lateral and adventitious roots; regulates development of fruit;
enhances apical dominance; functions in phototropism and gravitropism; promotes
vascular differentiation; retards leaf abscission
used in horticulture:
What are the major functions of Cytokines?
Regulate cell division in shoots and roots
modify apical dominance and promote lateral bud growth
promote movement of nutrients into sink tissues
stimulate seed germination; delay leaf senescence
Anti-aging
What are the major functions of GA?
Stimulate stem elongation, pollen development, pollen tube growth, fruit growth, and seed development and germination
regulate sex determination and the transition from juvenile to adult phases
What are the major functions of ABA?
Inhibits growth
promotes stomatal closure during drought stress;
promotes seed dormancy and inhibits early germination;
promotes leaf senescence;
promotes desiccation tolerance
What are the major functions of Ethylene?
Promotes ripening of many types of fruit, leaf abscission, and the triple response in seedlings (inhibition of stem elongation, promotion of lateral expansion, and horizontal growth);
enhances the rate of senescence
promotes root and root hair formation
promotes flowering in the pineapple family
What are the major functions of Brassinosteroids?
Promote cell expansion and cell division in shoots; promote root growth at low concentrations; inhibit root growth at high concentrations; promote xylem differentiation and inhibit phloem differentiation; promote seed germination and pollen tube elongation
What are the major functions of Jasmonates?
Regulate a wide variety of functions, including fruit ripening, floral development, pollen production, tendril coiling, root growth, seed germination, and nectar secretion; also produced in response to herbivory and pathogen invasion
What are the major functions of Strigolactones?
Promote seed germination, control of apical dominance, and the attraction of mycorrhizal fungi to the root
phototropism
Plants generally grow towards the light
Tropism
plant organs curving toward or away from a stimulus
Usually as a result of stem elongation
Auxins (indoleacetic acid, IAA)
Promote growth/elongation of the coleoptiles (stems above the cotyledons)
• Produced predominantly in the shoot tips (SAM)
• Moves unidirectional shoot tip to shoot base -> polar transport (unrelated to gravity)
coleoptiles
stems above the cotyledons)
Brassinosteroids
Steroids similar to cholesterol
Induce cell elongation and division in stems
Slow down leaf abscission
Promote xylem differentiation
Strigolactones
Xylem-mobile chemicals
Stimulate seed germination, suppress adventious root development, helps with mycorrhizae, controls apical dominance
How were the Strigolactones ID?
First ID’d from Striga (witchweed), a rootless parasitic plant that penetrate the roots of host plant
Jasmonates
Plant defense and plant development
First ID’d in jasmine plants
• Also works with phytochromes,GA,IAA,ethylene
Describe the role of Auxin in plant development?
Auxin produced in the shoot tip controls spatial organization of the plants –>Affects size, shape, environment of branches and stems
When auxin production decreases, lateral branches allowed to develop
Involved in phyllotaxy -> local peaks in auxin determine the site of the leaf primordia
Polar transport in leaf margins affects the formation of leaf veins
• Less auxin, more secondary leaf veins and loosely organized main veins
Reduction in auxin at the end of the growing season stimulates the reduction in the vascular cambium activity
Describe the role of Auxin in Stem elongation?
Binds to receptors in the plasma membrane to initiate cell expansion
• Stimulates growth when concentration is between 10-8 to 10-4 M
Also stimulates gene expression to, produce proteins, increase cytoplasmic fluids, and cell wall material
What is the acid growth hypothesis?
Auxin stimulates proton (H+) pumps along plasma membrane, increasing the membrane voltage and lowering pH inside of the cell
Acidification of the cell wall activates expansins, proteins that break the linkages (hydrogen bonds) in the cell walls
Increase in water potential due to increased ion uptake due to increasing membrane potential -> higher turgor pressure the cell is free to expand and contribute to stem elongation
How is auxin used in horticulture?
are used in horticulture:
• Rooting hormone for vegetative propagation
• Synthetic auxins are used as herbicides (die
from hormonal overdose)
• Synthetic auxins increase fruit production
expansin
Plant enzyme that breaks the cross-links (hydrogen bonds) between cellulose microfibrils and other cell wall constituents, loosening the wall’s fabric
Cytokinins
Discovered in the early 1940s
Stimulate cytokinesis (cell division)
Produced in actively growing tissues, particularly in the roots
Works with auxins to promote cell division and differentiation
Describe the role of cytokinins in apical domianance?
Apical bud suppresses growth of axillary buds
The apical bud is a sugar sink and produces auxins
2) Auxin moves downward, producing strigolactones that repress lateral bud growth
3) Cytokinin’s from the roots antagonizes effect of auxins and strigolactone, allowing limited lateral bud growth
4) Removal of apical bud allows remaining buds to receive more sugar and allow topmost lateral buds to assume apical dominance
How does cytokinins work in anti aging?
Slow apoptosis in cells
Inhibits protein breakdown, stimulates RNA and protein synthesis
Mobilizes nutrients from surrounding tissues
How do cytokinin and auxin work together?
Works with auxins to promote cell division and differentiation.
If just auxin present, cells will grow large but not divide
If just cytokinins,there is no effect
ratio of cytokinins to auxin controls cell differentiation.
When the concentrations of these two hormones are at certain levels, the mass of cells continues to grow, but it remains a cluster of undifferentiated cells called a callus
If cytokinin levels increase, shoot buds develop from the callus. If auxin levels increase, roots form