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Plant bio
Circadian rhythm in plants
| Question | Answer |
|---|---|
| Why is the planet biologically stressful? | - over 24hrs there are immense environmental changes of temperature, light inensity, humidity and predation |
| How is circadian rhythm in plants measured? | - time course analysis - plant first grown in light and dark cycles - then moved to a constant light or dark and temp, where the regulated biological processes run free |
| What properties are measured? | - period: time taken to complete a full cycle - phase: the time at which a particular point of cycle occurs - amplitude: the displacement of the oscillation from the centre point |
| Why are circadian plant rhythms important? | - plants with a functional circadian rhythm grow better - growth and development are critical to plant function - provides a fitness advantage - competition experiments showed when the exogenous period matches light-dark cycles, growth is accelerated |
| The circadian oscillator | - most circadian clocks are transcription-translation feedback loops - The protein encoded by Protein A: Gene A activates Gene B - The protein encoded by: Gene B represses Gene A |
| Simple biological oscillator | Reciprocal feedback loop • Negative feedback step • Speed of biochemical reactions adds a rate constant |
| Early arabidopsis circadian rhythm model | It is an oscillator with activation and suppression feedback (compare with previous slide) • The main genes involved are TOC1, LHY and CCA1 (TOC1 actually suppresses CCA1) |
| What is at the core of the circadian clock? | Reciprocal repression between CCA1 and TOC1 |
| Current model: more complex | - different components expressed at different times of the day - network models indicate connections between components, but lack temporal info about the clock function |
| What parts of the circadian system? | - entrainment pathways (from environment) - circadian oscillator - output pathways (gene) |
| Why is entrainment required? | The period of the circadian oscillator is approximately 24 h and there is natural variation between plants |
| Environmental signals that entrain the circadian oscillator | - red and blue light - sugars - temperature fluctuations |
Created by:
reub8n
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