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.

1. Cell and Developmental Biology
Module BS1003
Plant Cell and Developmental Biology
Pat Heslop-Harrison
phh4@le.ac.uk

2. • http://tinyurl.com/seedsBS1003

3. Cell and Developmental Biology
Module BS1003
Plant Cell and Developmental Biology
Pat Heslop-Harrison
phh4@le.ac.uk

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. 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. 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. 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. ‘Growth’ and light
CELL
EXPANSION
CELL
DIVISION

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. 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. Learning from textbooks
• Excellent presentation of facts
• How can you make your learning from
books active?

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. Learning and reflection
• What have you found difficult so far?

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. 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. 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. 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. Module Booklet
Lectures on Slideshare
Tinyurl.com/phhlight

22. 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

23. In the absence of
light we see:
ETIOLATION
LONG HYPOCOTYL
REDUCED LEAF EXPANSION
APICAL HOOK
PALE IN COLOUR
Photomorphogenesis
Etiolation or
Skotomorphogenesis

24. skoto- & photomorphogenesis in
potato
DE-ETIOLATION
IS DRAMATIC
Developmental
response to the light
signal!

25. Ecological significance of Etiolation
• TO MAXIMISE THE CHANCES OF
REACHING THE LIGHT BEFORE
FOOD RESERVES ARE EXHAUSTED
• ALL RESOURCES DIVERTED INTO
'VERTICAL' GROWTH

26. 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

27. 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

28. 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

29. 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!

31. http://tinyurl.com/lightbs1003
(or search YouTube – BS1003)

32. 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

33. PLANTS MUST BE ABLE TO DETECT
BOTH
RED
AND FAR-RED LIGHT
INDEPENDENTLY
• HOW DO PLANTS DETECT LIGHT?
• ABSORBING IT VIA PHOTORECEPTOR
MOLECULES!

34. 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

35. • 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

36. Pr
red
far red
Pfr
Phytochromes are reversibly photochromic

37. Phytochrome
absorption
spectrum
Absorbance
666
MODEL
PR
RED
FAR-RED
730
Wavelength (nm)
PFR >>>> BIOLOGICAL
ACTIVITY

38. • 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

39. 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)

40. PHYTOCHROME MODE OF
ACTION
Slow (some plants)

41. http://tinyurl.com/lightbs1003

42. WHERE IS PHYTOCHROME LOCALISED?
• APICAL REGIONS of the root and epicotyl,
where most of the dramatic developmental
changes occur

43. 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

44. 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

45. 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)

46. A model of phytochrome regulation of
rbcS & cab genes
Pfr
Pr
red
Pfr
Pfr
far red
PIF
Cytoplasm
Nucleus
Cell surface
CAB
Chloroplast
RBCS

47. 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

48. • 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

50. THE TRANSITION TO FLOWERING
1 meter
11 kg
Rafflesia arnoldii

51. 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

52. 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

53. Apical meristem
transformations
• Shoot apical
Inflorescence & floral meristems

54. 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

55. Development of a
single flower bud of
Arabidopsis
Coordinated growth
of different organs
P
P
C

56. FACTORS THAT INFLUENCE FLOWERING
PLANT AGE
LIGHT
TEMPERATURE

57. 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

58. 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

59. • Two GENERAL CHARACTERISTICS that could
be required for the ability to flower:
• THE CHRONOLOGICAL AGE OF THE PLANT
• THE LARGER SIZE OF THE PLANT

60. Century plant
(Agave americana)
Botanic Gardens
University of Leicester

61. LATE FLOWERING
MUTANTS
of Arabidopsis
Both OLD and LARGE
But still flower late
Genetic Control

62. 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

63. 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

64. WHY USE DAYLENGTH OR OTHER
ENVIRONMENTAL SIGNAL?
• PROVIDES A MEANS OF
SYNCHRONISING GROWTH AND
REPRODUCTION
•
•
- WITH EACH OTHER
- WITH THE ENVIRONMENT

65. Harry Allard photoperiod experiments

66. 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

67. 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

68. 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

69. •
BUT DAYLENGTH
CANNOT BE USED TO
DISTINGUISH
BETWEEN AUTUMN &
SPRING
Both have short nights, but very
different outcomes!

70. 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

71. 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.

72. 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

73. EVIDENCE?
• ‘BAGGING’
• GRAFTING
•
SDP
Cocklebur (Xanthium)

74. BAGGING EXPERIMENTS (Cocklebur= SDP)
Signal
LD
LD
Bagging of apical leaf on plant grown
in LONG DAYS (un-induced) leads to flowering

75. 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

76. • 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

77. • 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