Cell and Developmental Biology
Module BS1003
Plant Cell and Developmental Biology
Pat Heslop-Harrison
phh4@le.ac.uk
• http://tinyurl.com/seedsBS1003
Cell and Developmental Biology
Module BS1003
Plant Cell and Developmental Biology
Pat Heslop-Harrison
phh4@le.ac.uk
Practical Friday 25 October
Lab coats/ruler/pencil ...
• Watch YouTube videos
• Reminder how you set up tissue culture:
• ...
Aim: To

develop your knowledge &
understanding of the cell and developmental
biology of plants

Objectives: You should be...
In my lectures, I will try to bring up issues to
think about: you will need to read up more in the
textbooks (‘flip-teachi...
By the end of this lecture you will:
1. Have thought about active learning and how
you are learning at University
2. Know ...
‘Growth’ and light

CELL
EXPANSION
CELL
DIVISION
PHH: My use of Powerpoint Slides
• In general, I will talk about slides with
illustrations
• Slides with more bullet point...
Sources of information
• Text books:
– Reece et al. 2011 ‘Campbell Biology’ 9th edition
– Raven et al. 2009 ‘Biology’ 9th ...
Learning from textbooks
• Excellent presentation of facts
• How can you make your learning from
books active?
Learning from textbooks
• How can you make your learning from
books active?
• Look at small parts
• Look up parts from lec...
Learning and reflection
• What have you found difficult so far?
What have you found difficult so far?
• Scheduling and time planning
• Don’t get left behind!
• Notes, quizzing yourself
•...
What have you found difficult so far?
• Scheduling and time planning
• Don’t get left behind!
• Notes, quizzing yourself
•...
What have you found difficult so far?
• Scheduling and time planning
• Don’t get left behind!
• Notes, quizzing yourself
•...
Overview – 8 Lectures
Prof Dave Twell
8. Pattern Formation in Plants (Embryogenesis)
9. Meristems & Organogenesis
10. Chem...
Module Booklet
Lectures on Slideshare
Tinyurl.com/phhlight
Light important to plants for two reasons

Photosynthesis and Photomorphogenesis
• Photosynthesis - BS1013, Animal and Pla...
In the absence of
light we see:
ETIOLATION
LONG HYPOCOTYL
REDUCED LEAF EXPANSION
APICAL HOOK
PALE IN COLOUR

Photomorphoge...
skoto- & photomorphogenesis in
potato

DE-ETIOLATION
IS DRAMATIC
Developmental
response to the light
signal!
Ecological significance of Etiolation
• TO MAXIMISE THE CHANCES OF
REACHING THE LIGHT BEFORE
FOOD RESERVES ARE EXHAUSTED
•...
HOW IS LIGHT INVOLVED?
Only 10 min of white
light is sufficient to
initiate (or signal)
partial de-etiolation
Apical hook ...
Is photosynthesis involved in the deetiolation response?
Evidence?
DE-ETIOLATION CAN BE INDUCED
BY VERY SHORT BURSTS OF LI...
Are all wavelengths of light effective
at inducing de-etiolation?
• Expt. Test response to specific
wavelengths
• Result
•...
LETTUCE SEED GERMINATION
Germination response of lettuce seeds
to RED (650-680 nm) and
FAR-RED (710-750nm) wavelengths of ...
http://tinyurl.com/lightbs1003
(or search YouTube – BS1003)
LETTUCE SEED GERMINATION
• Response of lettuce seeds to RED and FAR-RED
• LIGHT TREATMENT

•
•
•
•
•
•

R
FR
R>FR
R>FR>R
R...
PLANTS MUST BE ABLE TO DETECT
BOTH

RED

AND FAR-RED LIGHT
INDEPENDENTLY

• HOW DO PLANTS DETECT LIGHT?
• ABSORBING IT VIA...
Chlorophyll
absorption
spectrum
selective

BLUE
•
•

Chlorophyll A absorption peaks at 432 nm
Chlorophyll B absorption pea...
• Following the discovery of the effects of red
and far red light……….
• the search was on for photoreceptors that
absorb a...
Pr

red
far red

Pfr

Phytochromes are reversibly photochromic
Phytochrome
absorption
spectrum

Absorbance

666

MODEL

PR

RED
FAR-RED

730

Wavelength (nm)

PFR >>>> BIOLOGICAL

ACTIV...
• Phytochrome
– Red- and far-red-light receptor
– Flips back and forth between 2
conformations
– Pfr – conformation that o...
THE PHYTOCHROME MOLECULE

C15

PROTEIN (124kd) + (CHROMOPHORE) via Thioether linkage
TWO IDENTICAL MONOMERS MAKE THE PHYTO...
PHYTOCHROME MODE OF
ACTION

Slow (some plants)
http://tinyurl.com/lightbs1003
WHERE IS PHYTOCHROME LOCALISED?

• APICAL REGIONS of the root and epicotyl,
where most of the dramatic developmental
chang...
Subcellular localisation
of Phytochrome?
• IMMUNOLOCALIZATI
ON: In etiolated
seedlings, DIFFUSE
• On illumination by red
l...
Shading responses
• Mediated by phytochrome
• Responses include the extension of leaves
from shady portions of a dense tre...
Phytochrome regulates growth &
development through gene activation
MODEL
PR

RED

PFR >>>> BIOLOGICAL ACTIVITY

FAR-RED

G...
A model of phytochrome regulation of
rbcS & cab genes

Pfr

Pr

red

Pfr

Pfr

far red

PIF

Cytoplasm
Nucleus

Cell surfa...
Photoperiodism
• Phytochromes play a critical role
• Influences the timing of dormancy
and flowering.
• Flowering plants c...
• Long-day plants – flower in spring or early
summer, when the night period is shorter (and
thus the day length is longer)...
THE TRANSITION TO FLOWERING

1 meter
11 kg

Rafflesia arnoldii
Light and other environmental factors
influence not only vegetative aspects of higher
plant development, contributing to t...
VEGETATIVE VERSUS REPRODUCTIVE GROWTH
Flower development involves a dramatic change in the
STRUCTURE and ACTIVITY of the S...
Apical meristem
transformations

• Shoot apical

Inflorescence & floral meristems
SUMMARY
• VEGETATIVE SHOOT APEX - simple structure
• 1. LEAF PRIMORDIA EMERGE IN A SPIRAL
ARRANGEMENT (PHYLLOTAXY)
• 2. RE...
Development of a
single flower bud of
Arabidopsis
Coordinated growth
of different organs

P
P

C
FACTORS THAT INFLUENCE FLOWERING
PLANT AGE
LIGHT
TEMPERATURE
Flowering Signals
• 1. PLANT AGE - JUVENILE
TO ADULT FORM
•

“RIPENESS-TOFLOWER”

• eg. Tobacco will only flower
after 15-...
Development of competence to flower
•
•
•
•

ENDOGENOUS TIMING MECHANISM?
DIFFUSIBLE FACTORS?
TEST IN GRAFTING EXPERIMENTS...
• Two GENERAL CHARACTERISTICS that could
be required for the ability to flower:

• THE CHRONOLOGICAL AGE OF THE PLANT
• TH...
Century plant
(Agave americana)
Botanic Gardens
University of Leicester
LATE FLOWERING
MUTANTS
of Arabidopsis
Both OLD and LARGE
But still flower late

Genetic Control
2. LIGHT: PHOTOPERIOD
•
•
•
•

SECOND MAJOR FACTOR
INFLUENCING THE
'DECISION' TO FLOWER
IS LIGHT (DAYLENGTH)

• 1. LONG DA...
SHORT DAY PLANT
Coffea arabica
Soybean
Strawberry
Chrysanthemum
Christmas cactus
Dahlias
Late summer/autumn
LONG DAY PLANT...
WHY USE DAYLENGTH OR OTHER
ENVIRONMENTAL SIGNAL?
• PROVIDES A MEANS OF
SYNCHRONISING GROWTH AND
REPRODUCTION
•
•

- WITH E...
Harry Allard photoperiod experiments
Relationship between photoperiod and flowering response
L IG H T

T R E A T M E N T F L O W E R IN G
SDP

Flower

Night br...
HOW DO PLANTS DETECT THE LENGTH
OF DARKNESS?
•

RED/FAR RED REVERSIBILITY OF THE PHOTOPERIODIC
RESPONSE

•
•
•
•
•

MODELS...
LONG DAY PLANTS > REQUIRE SHORT NIGHTS

• PFR PROMOTES FLOWERING
• INSUFFICIENT DEGRADATION OF PFR TO PR
• RED LIGHT BREAK...
•

BUT DAYLENGTH
CANNOT BE USED TO
DISTINGUISH
BETWEEN AUTUMN &
SPRING

Both have short nights, but very
different outcome...
3. TEMPERATURE
SOME PLANTS FLOWER MORE RAPIDLY
WHEN SEEDLINGS ARE GIVEN A COLD
TREATMENT:
• The promotion of flowering by ...
Vernalization
• Cabbage (biennial)
• Requires exposure to the
environmental cue of
prolonged winter cold to
flower the sec...
WHAT ABOUT INTERNAL (CELLULAR)
PHOTOPERIOD SIGNALLING
MECHANISMS?
• APPROPRIATE LIGHT IS DETECTED,
AND THE SIGNAL TRANSDUC...
EVIDENCE?
• ‘BAGGING’
• GRAFTING

•

SDP

Cocklebur (Xanthium)
BAGGING EXPERIMENTS (Cocklebur= SDP)
Signal

LD

LD

Bagging of apical leaf on plant grown
in LONG DAYS (un-induced) leads...
GRAFTING EXPERIMENTS (Cocklebur = SDP)
• graft SDinduced leaf
onto LDuninduced
stock
induces
flowering
repeat
cell memory
...
• FLOWERING SIGNAL MUST TRAVEL FROM LEAF TO
THE SHOOT APEX?
• MICHAEL CHAILAKHYAN (1930) POSTULATED A
CHEMICAL SIGNAL OR F...
• http://faculty.washington.edu/takato/i.html

• http://www.mpipz.mpg.de/25240/coupland_20

• And part 2
• And
www2.ju.edu...
BS1003 - Light and plant development lecture
BS1003 - Light and plant development lecture
BS1003 - Light and plant development lecture
BS1003 - Light and plant development lecture
BS1003 - Light and plant development lecture
BS1003 - Light and plant development lecture
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BS1003 - Light and plant development lecture

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Lecture for undergraduates on University of Leicester course BS1003 - Light and plant development.
It starts with some reflection on learning and approaches to study relevant to first year students, and then discusses the role of light in plant development, with a focus on experimental evidence.

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BS1003 - Light and plant development lecture

  1. 1. Cell and Developmental Biology Module BS1003 Plant Cell and Developmental Biology Pat Heslop-Harrison phh4@le.ac.uk
  2. 2. • http://tinyurl.com/seedsBS1003
  3. 3. Cell and Developmental Biology Module BS1003 Plant Cell and Developmental Biology Pat Heslop-Harrison phh4@le.ac.uk
  4. 4. Practical Friday 25 October Lab coats/ruler/pencil ... • Watch YouTube videos • Reminder how you set up tissue culture: • tinyurl.com/bs1003 • Results from carrot – Agrobacterium infection • tinyurl.com/carrotbs1003 • Or search YouTube for BS1003
  5. 5. Aim: To develop your knowledge & understanding of the cell and developmental biology of plants Objectives: You should be able to describe…. • The role of light in regulating growth and reproduction • Next lecture: The transition to flowering • End next week: the mechanisms involved in transferring foreign genes into plant cells
  6. 6. In my lectures, I will try to bring up issues to think about: you will need to read up more in the textbooks (‘flip-teaching’ – wiki). NB: flowering hormones (next lecture) is new since 2009 and you need to look in recent textbooks; wiki is poor on this too!
  7. 7. By the end of this lecture you will: 1. Have thought about active learning and how you are learning at University 2. Know about the information in light 3. Understand plant responses to light 4. Apply knowledge from Prof Twell’s lectures to a developmental question In my lectures, I will try to bring up issues to think about: you will need to read up more in the textbooks (‘flip-teaching’ – wiki). NB: flowering hormones (next lecture) is new since 2009 and you need to look in recent textbooks; wiki is poor on this too!
  8. 8. ‘Growth’ and light CELL EXPANSION CELL DIVISION
  9. 9. PHH: My use of Powerpoint Slides • In general, I will talk about slides with illustrations • Slides with more bullet points – Review what I have said – Remind ME if I have got away from the points I want to make – Help YOU with notes • Learning is active – I try to interact – so • Be ready to answer questions or discuss with your neighbours
  10. 10. Sources of information • Text books: – Reece et al. 2011 ‘Campbell Biology’ 9th edition – Raven et al. 2009 ‘Biology’ 9th edition – Brooker et al. 2013 ‘Biology’ 3rd edition – Sadava et al. 2013 ‘Life’ 10th edition
  11. 11. Learning from textbooks • Excellent presentation of facts • How can you make your learning from books active?
  12. 12. Learning from textbooks • How can you make your learning from books active? • Look at small parts • Look up parts from lectures • Ask yourself questions • Make notes • Design your own ‘exam’ questions – (often better than reading the given ones)
  13. 13. Learning and reflection • What have you found difficult so far?
  14. 14. What have you found difficult so far? • Scheduling and time planning • Don’t get left behind! • Notes, quizzing yourself • How-to-study books / websites
  15. 15. What have you found difficult so far? • Scheduling and time planning • Don’t get left behind! • Notes, quizzing yourself • How-to-study books / websites What new skills have you learnt?
  16. 16. What have you found difficult so far? • Scheduling and time planning • Don’t get left behind! • Notes, quizzing yourself • How-to-study books / websites What new skills have you learnt? • Learning from sources with more detail than you need • Learning from multiple sources • Coping with information overload
  17. 17. 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
  18. 18. Module Booklet Lectures on Slideshare Tinyurl.com/phhlight
  19. 19. Light important to plants for two reasons Photosynthesis and Photomorphogenesis • Photosynthesis - BS1013, Animal and Plant Physiology • Light in eliciting developmental programmes • Role of phytochrome, a light receptor molecule, in determining the responses of plants
  20. 20. In the absence of light we see: ETIOLATION LONG HYPOCOTYL REDUCED LEAF EXPANSION APICAL HOOK PALE IN COLOUR Photomorphogenesis Etiolation or Skotomorphogenesis
  21. 21. skoto- & photomorphogenesis in potato DE-ETIOLATION IS DRAMATIC Developmental response to the light signal!
  22. 22. Ecological significance of Etiolation • TO MAXIMISE THE CHANCES OF REACHING THE LIGHT BEFORE FOOD RESERVES ARE EXHAUSTED • ALL RESOURCES DIVERTED INTO 'VERTICAL' GROWTH
  23. 23. HOW IS LIGHT INVOLVED? Only 10 min of white light is sufficient to initiate (or signal) partial de-etiolation Apical hook unfolds Leaves expand Hypocotyl shows reduced elongation D W D + 10 min W
  24. 24. Is photosynthesis involved in the deetiolation response? Evidence? DE-ETIOLATION CAN BE INDUCED BY VERY SHORT BURSTS OF LIGHT ETIOLATED PLANTS DO NOT CONTAIN CHLOROPHYLL AND SO CANNOT ABSORB LIGHT EFFICIENTLY
  25. 25. Are all wavelengths of light effective at inducing de-etiolation? • Expt. Test response to specific wavelengths • Result • Red-light (650-680 nm) alone found to be sufficient to induce de-etiolation • Suggested that a red light absorbing photoreceptor existed
  26. 26. LETTUCE SEED GERMINATION Germination response of lettuce seeds to RED (650-680 nm) and FAR-RED (710-750nm) wavelengths of light DARK RED RED>FAR-RED NB: Modern varieties of lettuce are selected NOT to show this response: It is inconvenient for farmers and gardeners!
  27. 27. http://tinyurl.com/lightbs1003 (or search YouTube – BS1003)
  28. 28. LETTUCE SEED GERMINATION • Response of lettuce seeds to RED and FAR-RED • LIGHT TREATMENT • • • • • • R FR R>FR R>FR>R R>FR>R>FR R>FR>R>FR>R GERMINATION RESPONSE + + + Germination is promoted by Red Far-red reverses the response Response depends on the last light treatment Can operate over multiple cycles > SWITCH
  29. 29. PLANTS MUST BE ABLE TO DETECT BOTH RED AND FAR-RED LIGHT INDEPENDENTLY • HOW DO PLANTS DETECT LIGHT? • ABSORBING IT VIA PHOTORECEPTOR MOLECULES!
  30. 30. Chlorophyll absorption spectrum selective BLUE • • Chlorophyll A absorption peaks at 432 nm Chlorophyll B absorption peaks at 453 nm RED and 663 nm and 643 nm
  31. 31. • Following the discovery of the effects of red and far red light………. • the search was on for photoreceptors that absorb at those wavelengths. • 1964: A COMPOUND THAT SHOWED DIFFERENT ABSORPTION CHARACTERISTICS IN RED AND FAR-RED LIGHT WAS PURIFIED FROM ETIOLATED OAT (Avena sativa) SEEDLINGS • PHYTOCHROME H. William Siegelman & Firer USDA > 1964 Richard Vierstra & Peter Quail > 1983
  32. 32. Pr red far red Pfr Phytochromes are reversibly photochromic
  33. 33. Phytochrome absorption spectrum Absorbance 666 MODEL PR RED FAR-RED 730 Wavelength (nm) PFR >>>> BIOLOGICAL ACTIVITY
  34. 34. • Phytochrome – Red- and far-red-light receptor – Flips back and forth between 2 conformations – Pfr – conformation that only absorbs far-red light and activates cellular responses – When left in the dark, Pfr transforms to red light absorbing Pr • Pr can only absorb red light and cannot activate cellular responses – Lettuce seed germination experiments
  35. 35. THE PHYTOCHROME MOLECULE C15 PROTEIN (124kd) + (CHROMOPHORE) via Thioether linkage TWO IDENTICAL MONOMERS MAKE THE PHYTOCHROME DIMER ONE CHROMOPHORE TETRAPYRROLE PER MONOMER CHROMOPHORE CHANGES CONFORMATION UPON ILLUMINATION (cis-trans isomerization at Carbon15)
  36. 36. PHYTOCHROME MODE OF ACTION Slow (some plants)
  37. 37. http://tinyurl.com/lightbs1003
  38. 38. WHERE IS PHYTOCHROME LOCALISED? • APICAL REGIONS of the root and epicotyl, where most of the dramatic developmental changes occur
  39. 39. Subcellular localisation of Phytochrome? • IMMUNOLOCALIZATI ON: In etiolated seedlings, DIFFUSE • On illumination by red light (i.e. conversion to the active Pfr) LOCALISED to multiple sites within the cell >> nucleus!!! • ASSOCIATION WITH INTRACELLULAR RECEPTOR MOLECULES? • Phytochome interacting protein (PIF) DARK RED LIGHT
  40. 40. Shading responses • Mediated by phytochrome • Responses include the extension of leaves from shady portions of a dense tree canopy into the light, and growth that allows plants to avoid being shaded by neighboring plants • Occur by the elongation of branch internodes • Leaves detect shade as an increased proportion of far-red light to red light
  41. 41. Phytochrome regulates growth & development through gene activation MODEL PR RED PFR >>>> BIOLOGICAL ACTIVITY FAR-RED Gene activation • CAB = CHLOROPHYLL A/B BINDING PROTEIN • RUBISCO = (RIBULOSE 1,5-BIS PHOSPHATE CARBOXYLASE-OXYGENASE)
  42. 42. A model of phytochrome regulation of rbcS & cab genes Pfr Pr red Pfr Pfr far red PIF Cytoplasm Nucleus Cell surface CAB Chloroplast RBCS
  43. 43. 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
  44. 44. • 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
  45. 45. THE TRANSITION TO FLOWERING 1 meter 11 kg Rafflesia arnoldii
  46. 46. Light and other environmental factors influence not only vegetative aspects of higher plant development, contributing to the plant's overall shape, but also the transition to reproductive development, i.e. flowering. In particular we consider interactions of three factors, namely plant age, light (especially day length) and temperature in determining the transition to flowering
  47. 47. 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
  48. 48. Apical meristem transformations • Shoot apical Inflorescence & floral meristems
  49. 49. 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
  50. 50. Development of a single flower bud of Arabidopsis Coordinated growth of different organs P P C
  51. 51. FACTORS THAT INFLUENCE FLOWERING PLANT AGE LIGHT TEMPERATURE
  52. 52. 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
  53. 53. Development of competence to flower • • • • ENDOGENOUS TIMING MECHANISM? DIFFUSIBLE FACTORS? TEST IN GRAFTING EXPERIMENTS Eg.MANGO juvenile mature If the juvenile shoots, which normally fail to flower, are grafted on to a mature plant, they will flower
  54. 54. • Two GENERAL CHARACTERISTICS that could be required for the ability to flower: • THE CHRONOLOGICAL AGE OF THE PLANT • THE LARGER SIZE OF THE PLANT
  55. 55. Century plant (Agave americana) Botanic Gardens University of Leicester
  56. 56. LATE FLOWERING MUTANTS of Arabidopsis Both OLD and LARGE But still flower late Genetic Control
  57. 57. 2. LIGHT: PHOTOPERIOD • • • • SECOND MAJOR FACTOR INFLUENCING THE 'DECISION' TO FLOWER IS LIGHT (DAYLENGTH) • 1. LONG DAY PLANTS LDP 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
  58. 58. SHORT DAY PLANT Coffea arabica Soybean Strawberry Chrysanthemum Christmas cactus Dahlias Late summer/autumn LONG DAY PLANTS Wheat/Spinach Lettuce/Radish Beet/Clover Gladiolus/Iris Arabidopsis Late spring/Summer Kalanchoe SHORT DAYS (<8h) LONG DAYS (>12h) Poinsettia
  59. 59. WHY USE DAYLENGTH OR OTHER ENVIRONMENTAL SIGNAL? • PROVIDES A MEANS OF SYNCHRONISING GROWTH AND REPRODUCTION • • - WITH EACH OTHER - WITH THE ENVIRONMENT
  60. 60. Harry Allard photoperiod experiments
  61. 61. Relationship between photoperiod and flowering response L IG H T T R E A T M E N T F L O W E R IN G SDP Flower Night break inhibits flowering in SDP Promotes flowering in LDP Day break no effect RES P O N SE LDP Vegetative Vegetative Flower Vegetative Flower Vegetative Flower Length of the DARK PERIOD determines the flowering response In both SDP & LDP
  62. 62. 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
  63. 63. 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
  64. 64. • BUT DAYLENGTH CANNOT BE USED TO DISTINGUISH BETWEEN AUTUMN & SPRING Both have short nights, but very different outcomes!
  65. 65. 3. 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
  66. 66. 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.
  67. 67. WHAT ABOUT INTERNAL (CELLULAR) PHOTOPERIOD SIGNALLING MECHANISMS? • APPROPRIATE LIGHT IS DETECTED, AND THE SIGNAL TRANSDUCED INTO A RESPONSE AT THE SHOOT APEX • LEAF (not the apical meristem) IS THE SITE OF DETECTION OF PHOTOPERIOD
  68. 68. EVIDENCE? • ‘BAGGING’ • GRAFTING • SDP Cocklebur (Xanthium)
  69. 69. BAGGING EXPERIMENTS (Cocklebur= SDP) Signal LD LD Bagging of apical leaf on plant grown in LONG DAYS (un-induced) leads to flowering
  70. 70. 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
  71. 71. • FLOWERING SIGNAL MUST TRAVEL 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 travels to shoot apical meristem • In SAM, FT protein combines with another protein and acts as transcription factor for flower induction genes
  72. 72. • http://faculty.washington.edu/takato/i.html • http://www.mpipz.mpg.de/25240/coupland_20 • And part 2 • And www2.ju.edu.jo/sites/Academic/tamimi/Mat erial/Fflower.ppt&ei=qPNnUoflDbSg0wWzjY HQCA&usg=AFQjCNGb1dG34gBOdILat7ZfR IcSQQrpag&sig2=Icn04C7ZjwyC0lDjAhbmb g&bvm=bv.55123115,d.d2k https://www.google.co.uk/url?sa=t&rct=j&q=&e
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