Plant Control Systems Flashcards
(128 cards)
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.