BS1003: The transition to flowering. Pat Heslop-Harrison

1,193 views

Published on

Lecture 2 from Pat Heslop-Harrison for BS1003 - Cell and Developmental Biology. The transition to flowering. How do plants decide to flower? How do they respond to daylength (photoperiod) and temperature? For information from light, phytochrome is the photoreceptor, but not the clock/time measuring process. Pfr (phytochrome far red) is always the active form of phytochrome, but the function is different in long day plants and short day plants. Pfr promotes flowering in LDPs but inhibits flowering in SDPs.

0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,193
On SlideShare
0
From Embeds
0
Number of Embeds
22
Actions
Shares
0
Downloads
78
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

BS1003: The transition to flowering. Pat Heslop-Harrison

  1. 1. Cell and Developmental Biology Module BS1003 Lectures on Slideshare and blackboard (under Schwarzacher) Plant Cell and Developmental Biology Tinyurl.com/phhLight Tinyurl.com/phhFlowering Pat Heslop-Harrison phh4@le.ac.uk
  2. 2. Sugar beet seed genetics • Change from multigerm with several seeds joined together • To monogerm with single seeds – giving the 40% yield increase of the Metro article • Genetic character (cf lettuce and seed germination)
  3. 3. Cell and Developmental Biology Module BS1003 Lectures on Slideshare and blackboard (under Schwarzacher) Plant Cell and Developmental Biology Tinyurl.com/phhLight Tinyurl.com/phhFlowering Pat Heslop-Harrison phh4@le.ac.uk
  4. 4. British Sugar. Display at Cereals 2012.
  5. 5. Aim: To develop your knowledge & understanding of the cell and developmental biology of plants Objectives: You should be able to describe…. • Last lecture: The role of light in regulating growth - photomorphogenesis • The transition to flowering • Next up: Dr Trude Schwarzacher on genomics and biotechnology
  6. 6. By the end of this lecture you will: 1. How do plants „decide‟ when to flower? Flowering is seasonal (in temperate regions) Why? Much about flowering is new since 2009 and you need to look in recent textbooks; Wikipedia is (unusually) poor on this topic!
  7. 7. By the end of this lecture you will: 1. How do plants „decide‟ when to flower 2. How is temperature sensed? 3. How is daylength sensed? Much about flowering is new since 2009 and you need to look in recent textbooks; Wikipedia is (unusually) poor on this topic! http://tinyurl.com/FlowerCues Andrés F, Coupland G. 2012. The genetic basis of flowering responses to seasonal cues. Nature Reviews Genetics 13, 627-639. (Sept 2012). doi:10.1038/nrg3291 – much of this lecture!
  8. 8. THE TRANSITION TO FLOWERING 1 meter 11 kg Rafflesia arnoldii
  9. 9. Photoperiodism • Phytochromes play a critical role • Influences the timing of dormancy and flowering. • Flowering plants can be classified as long-day, short-day, or day-neutral plants according to the way their flowering responds to night length • Plants measure night length
  10. 10. • Long-day plants – flower in spring or early summer, when the night period is shorter (and thus the day length is longer) than a defined period • Short-day plants – flower only when the night length is longer than a defined period such as in late summer, autumn or winter, when days are short • Day-neutral plants – flower regardless of the night length, as long as day length meets the minimal requirements for plant growth
  11. 11. VEGETATIVE VERSUS REPRODUCTIVE GROWTH Flower development involves a dramatic change in the STRUCTURE and ACTIVITY of the SHOOT APEX Vegetative meristem Inflorescence meristem Leaf primordia Flower primordia Floral meristem Floral organ primordia
  12. 12. Apical meristem transformations • Shoot apical meristem Inflorescence & floral meristems
  13. 13. SUMMARY • VEGETATIVE SHOOT APEX - simple structure • 1. LEAF PRIMORDIA EMERGE IN A SPIRAL ARRANGEMENT (PHYLLOTAXY) • 2. REPETITIVE • 3. INDETERMINATE FLORAL APEX - more complex 1. SHOOT STOPS ELONGATION GROWTH 2. INITIATES MULTIPLE FLORAL ORGANS 3. NON-REPETITIVE 4. DETERMINATE
  14. 14. Development of a single flower bud of Arabidopsis Coordinated growth of different organs P P C
  15. 15. FACTORS THAT INFLUENCE FLOWERING Plant age Light Information Temperature
  16. 16. Flowering Signals • 1. PLANT AGE - JUVENILE TO ADULT FORM • “RIPENESS-TOFLOWER” • eg. Tobacco will only flower after 15-20 nodes • eg. Many tree species flower only after >10 years
  17. 17. Development of competence to flower • ENDOGENOUS TIMING MECHANISM? • DIFFUSIBLE FACTORS? • TEST IN GRAFTING EXPERIMENTS • MANGO juvenile mature If the juvenile shoots, which normally fail to flower, are grafted on to a mature plant, they will flower
  18. 18. • Two GENERAL CHARACTERISTICS that could be required for the ability to flower: • THE CHRONOLOGICAL AGE OF THE PLANT • THE LARGER SIZE OF THE PLANT
  19. 19. Century plant (Agave americana) Botanic Gardens University of Leicester
  20. 20. LATE FLOWERING MUTANTS of Arabidopsis Both OLD and LARGE But still flower late Genetic Control
  21. 21. SHORT DAY PLANT Coffea arabica Soybean Strawberry Chrysanthemum Christmas cactus Dahlias Late summer/autumn LONG DAY PLANTS Wheat/Spinach Lettuce/Radish Gladiolus/Iris Arabidopsis Primrose Late spring/summer Poinsettia Christmas Cactus SDP Primula primrose/ cowslip LDP
  22. 22. LIGHT: Duration or photoperiod • • • • LDP SECOND MAJOR FACTOR INFLUENCING THE 'DECISION' TO FLOWER IS LIGHT (DAYLENGTH) • 1. LONG DAY PLANTS Photoperiod(h) Flowering Response SDP • 2. SHORT DAY PLANTS • 3. DAY-NEUTRAL PLANTS • eg. tobacco, tomato, sunflower • dandelions, cucumbers, roses, snapdragons, carnations, cotton CDL = Critical Daylength Day Neutral
  23. 23. WHY USE DAYLENGTH OR OTHER ENVIRONMENTAL SIGNAL? • Predicts future season/weather • Allows synchronization of growth and reproduction • - WITH EACH OTHER PLANT • - WITH THE ENVIRONMENT
  24. 24. • BUT DAYLENGTH CANNOT BE USED TO DISTINGUISH BETWEEN AUTUMN & SPRING Both have short nights, but very different outcomes!
  25. 25. Harry Allard photoperiod experiments Tournois (1914) first noted
  26. 26. Relationship between photoperiod and flowering response LI H T G N TREA TM EN T FLO W ERI G SD P Flower Night break inhibits flowering in SDP Promotes flowering in LDP Day break no effect RESPO N SE LD P Vegetative Vegetative Flower Vegetative Flower Vegetative Flower Length of the DARK PERIOD determines the flowering response In both SDP & LDP
  27. 27. HOW DO PLANTS DETECT THE LENGTH OF DARKNESS? • RED/FAR RED REVERSIBILITY OF THE PHOTOPERIODIC RESPONSE • • • • • MODELS: SD PLANTS - REQUIRE LONG NIGHTS - PFR IS DEGRADED TO PR - PFR INHIBITS FLOWERING - LOW PFR SIGNALS FLOWERING • RED LIGHT NIGHT BREAK PREVENTS FLOWERING BY CONVERTING PR TO PFR - inhibitor PR RED PFR >>>> BIOLOGICAL ACTIVITY INHIBIT FLOWERING FAR-RED/DARK
  28. 28. LONG DAY PLANTS > REQUIRE SHORT NIGHTS • PFR PROMOTES FLOWERING • INSUFFICIENT DEGRADATION OF PFR TO PR • RED LIGHT BREAK IN A LONG DARK PERIOD INDUCES FLOWERING BY PREVENTING DEGRADATION OF PFR TO PR PR RED PFR >>>> BIOLOGICAL ACTIVITY PROMOTE FLOWERING FAR-RED/DARK
  29. 29. TEMPERATURE • SOME PLANTS FLOWER MORE RAPIDLY WHEN SEEDLINGS ARE GIVEN A COLD TREATMENT: • The promotion of flowering by cold is known as • VERNALIZATION • EFFECTIVE TEMPERATURE -2 to +120C • Eg. Autumn sown, Winter wheat/Winter rye • Long term Winter „memory‟ winter > summer (~200 days) • Many biennials > rosette form over winter > flower spring/early summer
  30. 30. Sugar beet: biennial crop flowering in „second‟ year Plant early for maximum establishment and growth before winter
  31. 31. Vernalization • Cabbage (biennial) • Requires exposure to the environmental cue of prolonged winter cold to flower the second spring after planting. Cabbage grown in the greenhouse for 5 years without vernalization.
  32. 32. Where are the signals detected and how? • APPROPRIATE light or temperature IS DETECTED, AND THE SIGNAL TRANSDUCED INTO A RESPONSE AT THE SHOOT APEX – perhaps months later • LEAF (not the apical meristem) IS THE SITE OF DETECTION OF PHOTOPERIOD
  33. 33. EVIDENCE? • „BAGGING‟ • GRAFTING • SDP Cocklebur (Xanthium) –Bonner & Hamner
  34. 34. BAGGING EXPERIMENTS (Cocklebur= SDP) Signal LD LD Bagging of apical leaf on plant grown in LONG DAYS (un-induced) leads to flowering
  35. 35. GRAFTING EXPERIMENTS (Cocklebur = SDP) • graft SDinduced leaf onto LDuninduced stock induces flowering repeat cell memory Signal moves leaf to apex SD LD LD LD LD LD
  36. 36. • FLOWERING SIGNAL TRAVELS FROM LEAF TO THE SHOOT APEX • MICHAEL CHAILAKHYAN (1930) POSTULATED A CHEMICAL SIGNAL OR FLOWERING HORMONE FLORIGEN • 2007: FT-protein is + „florigen‟ (George Coupland) • mRNA and protein made in leaf phloem companion cells in response to light perception • Protein (small – 20kD) travels in phloem to SAM • In SAM, FT protein combines with another protein and acts as transcription factor for flower induction genes • Arabidopsis molecular genetics enabled progress • (NB: Big change: need post-2009 textbook; Wikipedia is poor!)
  37. 37. Tinyurl.com/FlowerCues Fernando Andrés & George Coupland “Expression of key transcription factors in A. thaliana is regulated by day length or by temperature, creating plasticity in flowering behaviour so that it occurs only under certain environmental conditions. These environmentally responsive transcription factors converge on a small number of floral integrator genes that initiate the early stages of flowering, and this convergence creates a coordinated response to seasonal cues.”
  38. 38. In Arabidopsis, CO (=constans gene) codes for a transcription factor protein that activates FT gene FT mRNA then transcribed to FT protein and transported to shoot apical meristem (Andres & Coupland)
  39. 39. From Sadava et al. Life: the science of biology. 10th Edition
  40. 40. Complex regulation of transcription factor genes, TF proteins, dependent mRNA transcription and translation!
  41. 41. Overview – 8 Lectures Prof Dave Twell 8. Pattern Formation in Plants (Embryogenesis) 9. Meristems & Organogenesis 10. Chemical Communication Systems in Plants Prof Pat Heslop-Harrison 11. The Role of Light in Plant Development 12. The Transition to Flowering Dr Trude Schwarzacher 13. The Biology of Crown Gall 14. Genetic Engineering of Plant Development 15. Genes, Genomes & Genomics in Plants
  42. 42. Module Booklet Lectures on Slideshare Tinyurl.com/phhflowering Tinyurl.com/phhlight
  43. 43. Information in light: Quantity/Intensity Quality/Wavelength Direction Periodicity/Daylength
  44. 44. Phytochrome regulates growth & development through gene activation MODEL PR RED PFR >>>> BIOLOGICAL ACTIVITY FAR-RED or Dark (slow) Gene activation (includes +ve and –ve responses) See YouTube – BS1003 Phytochrome practical
  45. 45. Relationship between photoperiod and flowering response LI H T G N TREA TM EN T FLO W ERI G SD P Flower Night break inhibits flowering in SDP Promotes flowering in LDP Day break no effect RESPO N SE LD P Vegetative Vegetative Flower Vegetative Flower Vegetative Flower Length of the DARK PERIOD determines the flowering response In both SDP & LDP
  46. 46. • FLOWERING SIGNAL TRAVELS FROM LEAF TO THE SHOOT APEX • MICHAEL CHAILAKHYAN (1930) POSTULATED A CHEMICAL SIGNAL OR FLOWERING HORMONE FLORIGEN
  47. 47. From Sadava et al. Life: the science of biology. 10th Edition • • • • 2007: FT-protein is + „florigen‟ mRNA and protein detects light; made in leaf Protein travels in phloem to SAM In SAM, FT protein is transcription factor for flower induction genes
  48. 48. Cell and Developmental Biology Module BS1003 Lectures on Slideshare and blackboard (under Schwarzacher) Plant Cell and Developmental Biology Tinyurl.com/phhLight Tinyurl.com/phhFlowering Tinyurl.com/FlowerCues Pat Heslop-Harrison phh4@le.ac.uk

×