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16 Cards in this Set
- Front
- Back
All plant organs can undergo senescence: |
- flower senescence - senescence of fruit - whole aerial part of plant in annuals: monocarpic senescence - sequential leaves in perennial herbaceous plants |
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Senescence involved remobilisation of nutrients: |
- breakdown of macromolecules (hydrolytic enzymes) - the building blocks are transported back into other parts of the plant for growth and storage e.g. chloroplast proteins are major nitrogen and phosphorus resources in green tissues (RubisCo - N, plastid ribosomes - P) |
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The life span of leafs vary: |
2) arabidopsis leaves = life of the planst ~ weeks 3) bristlecone pine needles can last up to 40 yrs |
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Life span of petals varies greatly as well |
- hemerocallis - 24 h - Phaleonopsis - months |
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How is senescence regulated? |
- Ethylene - peak concentration is reached right before visible signs of senescence |
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What are the stages of flower development and senescence? |
- closed bud cell (division/expansion) = Nutrient sink - Open flower, PCD beginning in mesophyl = nutrient sink - Wilting flower, PCD is widespread = nutrient source - Petals and other organs are abscised = abscission zones |
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Loss of internal cell integrity: |
- mesophyll cells die first - electrolyte leakage increases when cells die |
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What hormones regulate senescence in plants? |
- ABA - abscisic acid - ROS - reactive oxygen species - JA - jasmonic acid - SA - salicylic acid |
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How is senescence regulated in plants? |
1) stress or developmental signal 2) hormonal signal 3) hormonal receptor 4) MAP kinase cascade 5) Network of transcription factors 6) gene activation for remobilisation and cell death |
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Cell death in response to abiotic factors: |
1) heat
2) ozone 3) UV |
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What happens in response to heat? |
- cytological response
- chromosome condensation, cytoplasm shrinkage; e.g. heat shock in tobacco; increase in ROS, DNA laddering, gene expression changes |
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What happens in response to ozone? |
- ethylene and salicylic acid stimulate ozone-induced cell death; - DNA fragmentation, increase of ROS, early release of cyt C - activation of proteases - chromatin condensation - blebbing of plasma membrane - up regulation of genes |
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What happens in response to UV? |
- In arabidopsis - induced death is dose and light dependent - DNA laddering - changes in nuclear morphology - caspase inhibitors or expression of DAD1 blocks PCD |
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Cell death in response to biotic factors (2) |
- self incompatible pollination - responses to pathogens |
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How does cell death in the pollen tube takes place? |
- Ca2+ signalling - cytoskeletal changes - ROS and NO involved - caspase activity required |
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How does the cell death in response to pathogens take place (hypersensitive response)? |
- restricts growth of pathogen (seen as lesions) - Receptors recognise pathogen signals - oxidative burst and ion fluxes - intracellular signalling is triggered - activation of defence responses - activation of PCD - activation of cell protection mechanisms to regulate the PCD |