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Plant bio

Plant hormones II

QuestionAnswer
Ethylene •Control of fruit ripening •Control of leaf and petal senescence •Stress responses
Ethylene is a gas Biosynthesis begins with Methionine • ACS is ACC synthase; ACO is ACC oxidase
The receptors negatively regulate the responses - When not bound to ethylene, the receptor shuts off the ethylene response - When bound to ethylene, the receptor does not shut off the ethylene response
Fruit ripening is induced by ethylene Ethylene is a gaseous hormone that promotes fruit softening and flavor and color development
Ethylene promotes senescence Ethylene promotes leaf and petal senescence Ethylene levels can be managed to maintain fruit freshness, commercially and at home
Abscisic Acid (ABA) • Stomatal aperture • Stress responses
ABA synthesis is strongly induced in response to stress - ABA levels are tightly controlled - ABA levels rise during drought stress due in part to increased biosynthesis and seed germination - ABA can be transported within the plant, from root to shoot and then to guard cells
ABA signal transduction affects gene expression When ABA is present, inactivation of the PP2C phosphatase permits a protein kinase (e.g. SnRK) to phosphorylate and activate ABA-inducible TFs, promoting transcription of ABA-inducible genes
ABA regulates stomatal aperture by changing the volume of guard cells via stomata Guard cells open and close stomata for gas exchange: a fine balance is required to allow CO2 in for photosynthesis and prevent excessive water loss • ABA induced by drought causes the guard cells to close and prevents their reopening, conserving water
ABA-induced stomatal closure is extremely rapid and involves changes in ion channel activities ABA triggers an increase in cytosolic calcium (Ca2+), which activates channels allowing Cland K+- to leave the cell As ions leave the cell, so does water (by osmosis), causing the cells to lose volume and close over the pore
Hormonal responses to biotic stress Bacteria, fungi, viruses – Biotrophic organisms Herbivores – insects, other animals, fungi – Necrotrophic organisms
Jasmonates •Response to necrotrophic pathogens •Induction of antiherbivory responses •Production of herbivore-induced volatiles to prime other tissues and attract predatory insects
Jasmonic acid (JA) and its metabolite methyl jasmonate contribute to systemic defence responses Defence responses are activated in distant tissues
Jasomonates stimulate production of volatile signaling compounds Herbivore-induced volatiles prime other tissues (and other plants) for attack making them unpalatable (indicated in red)
JA-induced changes in gene expression Low JA-Ile: no transcription
Jasmonates induce the expression of anti-herbivory chemicals Wound-induced signals insect oral secretions Protease inhibitors Feeding deterants
Salicylic Acid •Response to biotrophic pathogens •Induced defense response •Systemic acquired resistance
Most SA is synthesized in the chloroplast, conjugated in the cytoplasm and sequestered in the vacuole
Salicylates contribute to acquired and systemic acquired resistance SA is necessary in systemic tissue for SAR, but the nature of the mobile signal(s) is still up in the air It is likely that multiple signals contribute to SAR
Grafting studies suggest that SA itself is NOT the mobile signal - Plants expressing NahG degrade SA and prevent its accumulation
- Leaves of rootstock were inoculated with a virus, then upper scion leaves challenged with the virus. Healthy scion leaves indicates SAR and means the mobile signal was produced in the inoculated leaves
Regulation of SA accumulation SA synthesis is induced by pathogens or stress. Genetic studies have identified some of the signals that transduce pathogen perception to SA synthesis
NPR1 itself is activated by binding to SA NPR1 binds SA, triggering a conformational change that releases its C-terminal activation domain from inhibition to trigger transcription
Physical barriers exclude most microorganisms Some pathogens enter through wounds or stomata
PAMP recognition triggers PAMP Triggered Immunity Pathogen-associated molecular patterns (PAMPs) are conserved molecules like flagellin or chitin They are perceived by extracellular receptors called PRRs (pattern recognition receptors)
PAMP perception triggers SA synthesis and defense gene induction – this is called patterntriggered immunity (PTI)
The hypersensitive response involves cell death Pathogen Response (PR) genes Antimicrobial compounds Strengthening of plant cell walls Programmed cell death Hypersensitive response (HR)
The hypersensitive response seals the pathogen in a tomb of dead cells - The HR kills the infected cells and cells surrounding them and prevents the pathogen from spreading - Without a hypersensitive response, the pathogen can multiply
Created by: reub8n
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