STARTER– Topic 9 MCQS• 1. C• 2. C• 3. B• 4. A• 5. C• 6. B• 7. B
• 8. C• 9. B• 10. C• 11. D• 12. C• 13. C
Learning Objectives
• Outline the metabolic processes during germination of a starchy seed.
• Explain how flowering is controlled in long-day and short-day plants, including the role of phytochrome.
Definitions
Phytochrome• protein pigment held in plant leaves• has two distinct but interchangeable forms:• PR (or P660) and PFR (P735)
Photoperiod • the number of daylight hours in a 24hr cycle• varies with the seasons
Phytochrome and the photoperiod
PR PFR
Rapid conversion in daylight
Slow dark reconversion
Phytochrome and the photoperiod
PR PFR
Rapid conversion in daylight
Slow dark reconversion
So the ratio of PR to PFR at dawn gives a measure of the changing seasons…
Phytochrome and the photoperiod
If PR:PFR at dawn is falling, the days are getting……longer meaning that……summer is coming
PR PFR
Rapid conversion in daylight
Slow dark reconversion
Phytochrome and the photoperiod
If PR:PFR at dawn is rising, the days are getting……shorter meaning that……winter is coming
PR PFR
Rapid conversion in daylight
Slow dark reconversion
Phytochrome and the photoperiod
This means that plants can react to coming seasons and prepare physiologically for them
PR PFR
Rapid conversion in daylight
Slow dark reconversion
Phytochrome and flowering
• One clear example of physiological response to the seasons is flowering
• Plants need to have flowers mature when insects become abundant to increase chances of pollination
• Development of flowers is a slow process and needs to begin long before insects appear
Long and short day species• In all plants flowering is brought about by the hormone Florigen
• Long day species are those which flower in response to long days (short nights)PFR is the trigger for florigen secretion
• Short day species are those which flower in response to short days (long nights)PR is the trigger for florigen secretion
• In day neutral species some other trigger (e.g. temperature causes flowering)
Poinsettia: a short day species
Spinach: a long day species
Simulating long nights
• A brief exposure of plants to pure far red light causes a rapid conversions of PFR to PR
PR PFR
Flash of far red light
This replaces the need for long periods of darkness to stimulate flowering in SDS and has commercial applications
Demo time!
• + = flowering, _ = no flowering
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• + = flowering, _ = no flowering
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• + = flowering, _ = no flowering
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• + = flowering, _ = no flowering
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• + = flowering, _ = no flowering