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.

http://click4biology.info/c4b/9/plant9.3.htm#1

http://trc.ucdavis.edu/biosci10v/bis10v/media/ch19/day_length.swf

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

http://glencoe.mcgraw-hill.com/sites/9834092339/student_view0/chapter41/animation_-_phytochrome_signaling.html

Demo time!

http://trc.ucdavis.edu/biosci10v/bis10v/media/ch19/day_length.swf

• + = 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

http://www.ucopenaccess.org/courses/CPBiology/bio_5_3_2_3.swf