Plant signalling 2 Flashcards
What are phytohormones?
Characterized by the property of serving as chemical
messengers, by which the activity of certain organs is coordinated with that of others.
*Phytohormones regulate cellular activities (division, elongation and differentiation), pattern formation, organogenesis, reproduction, sex determination, and responses to abiotic and biotic stress.
Give some examples of phytohormones
Plants use a range of molecules for sending signals which help co-ordinate growth and development
Auxin
Cytokinin
Gibberellins
Strigolactones
Brassinosteroids
Ethylene (flowering and reproduction lecture)
Abscisic Acid
Salicylic Acid (plant immunity)
Jasmonic Acid
Physiological and developmental responses may be brought about by the action of Phytohormones describe process?
production of phytohormone–>transport–> signal transduction–> gene expression–> response
Receptors can be membrane-bound
Name a few
Hormone binding initiates an information relay
ethylene
cytokinins
brassinosteroids
What can hormones act like?
What do soluble receptors facilitate?
Hormones can act like “molecular glue”
Soluble receptors can facilitate interactions between proteins
What happens when receptors interact with hormones e.g (auxin)?
Some receptors initiate protein proteolysis
The hormones bind to receptors, initiating proteolysis of repressors to activate a transcriptional regulator.
What is proteolysis?
Proteolysis is a hydrolysis reaction of peptide bonds in which proteins breakdown into smaller peptides and/or into individual amino acid residues. The proteolytic cleavage reactions are usually catalyzed by either chemicals or enzymes.
What happens if we disrupt hormone synthesis?/response
It interferes with elongation and normally produces dwarf mutants.
What is Auxin (many types but main/predominant one= Indole-3-acetic acid (IAA)
Involved in;
Growth
Phototropism and gravitropism
Branching
Embryonic patterning
Stem cell maintenance
Organ initiation
Lateral organ initiation at the shoot apical meristem
Inhibit branching in the shoot
Promote branching in the root
Maintain stem cell fate at the root apical meristem
Patterning and vascular development
Auxin mediates the phototropic response
What are Cytokinins?
They are involved in;
Cell division
Control of leaf senescence
Control of nutrient allocation
Root nodule development
Stem cell maintenance
Regulate auxin action
What do Cytokinins act as?
Where do auxin and cytokinins regulate eachother’s function?
They act antagonistically to auxins
Promote stem cell fate at the shoot apical meristem
Promote branching in the shoot
Promote differentiation at the root apical meristem
Inhibit branching in the shoot
auxins do the opposite
*At the root apex
Taking advantage of the antagonistic interaction between auxin and cytokinins: Plant tissue culture
Most plant cells are totipotent (just undifferentiated cells but they all have the genetic material to give rise to an actual plant)
Plant cell differentiation and organogenesis can be manipulated in cell culture.
Undifferentiated plant cells grown in tissue culture are termed callus
The ratio of specific phytohormones determines how callus will develop.
Plant tissue culture experiment
What are the 4 main phytohormones used in tissue culture?
What could these experiments tell (skoog.f)
Cytokinin e.g. kinetin (cell division)
Auxin (NAA rather than IAA)
Gibberellins
Abscisic Acid (ABA)
Cytokinin:Auxin ratio (and absolute concentration) determines organogenesis and absolute ratios required vary with plant species
High Cytokinin : Low Auxin for shoots
High Auxin : Low Cytokinin for roots and for establishing an embryogenic callus
Gibberellins and ABA are used only in some treatments and only to enhance growth
Cytokinins affect grain production and drought tolerance in rice and tobacco plants.
*Rice plants that accumulate more CK can produce more grain per plant because of changes in inflorescence architecture.
*Tobacco plants that produce more CK are more drought tolerant because of the delay in leaf senescence conferred by CK.
What can strigolactones do?
Strigolactones, synthesized from carotenoids, are produced in plant roots. They attract mycorrhizal fungi and promote the germination of parasitic plants of the genus Striga.
Strigolactones inhibit branch outgrowth
Auxin transported from the shoot to the root induces strigolactone synthesis, which indirectly inhibits bud outgrowth.
In a rice mutant that does not produce strigolactones, tillers (lateral branches)grow out.
