bs1003 - light and plant development lecture
DESCRIPTION
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.TRANSCRIPT
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Cell and Developmental BiologyModule BS1003
Plant Cell and Developmental BiologyPlant Cell and Developmental Biology
Pat Heslop-HarrisonPat Heslop-Harrison
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Cell and Developmental BiologyModule BS1003
Plant Cell and Developmental BiologyPlant Cell and Developmental Biology
Pat Heslop-HarrisonPat Heslop-Harrison
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Practical Friday 25 OctoberLab 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
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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
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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!
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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 light3. Understand plant responses to light4. 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!
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‘Growth’ and light
CELL EXPANSION
CELL DIVISION
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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
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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
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Learning from textbooks• Excellent presentation of facts
• How can you make your learning from books active?
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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)
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Learning and reflection
• What have you found difficult so far?
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• Scheduling and time planning• Don’t get left behind!• Notes, quizzing yourself• How-to-study books / websites
What have you found difficult so far?
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• Scheduling and time planning• Don’t get left behind!• Notes, quizzing yourself• How-to-study books / websites
What have you found difficult so far?
What new skills have you learnt?
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• Scheduling and time planning• Don’t get left behind!• Notes, quizzing yourself• How-to-study books / websites
• Learning from sources with more detail than you need
• Learning from multiple sources• Coping with information overload
What have you found difficult so far?
What new skills have you learnt?
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Overview – 8 LecturesProf Dave Twell8. Pattern Formation in Plants (Embryogenesis)9. Meristems & Organogenesis10. Chemical Communication Systems in Plants
Prof Pat Heslop-Harrison11. The Role of Light in Plant Development12. The Transition to FloweringDr Trude Schwarzacher13. The Biology of Crown Gall14. Genetic Engineering of Plant Development15. Genes, Genomes & Genomics in Plants
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Module Booklet
Lectures on SlideshareTinyurl.com/phhlight
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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
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In the absence of light we see: ETIOLATION
Photomorphogenesis
Etiolation orSkotomorphogene
sis
LONG HYPOCOTYLREDUCED LEAF EXPANSIONAPICAL HOOKPALE IN COLOUR
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skoto- & photo-morphogenesis
in potato
DE-ETIOLATION IS DRAMATIC Developmental response to the light signal!
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Ecological significance of Etiolation
• TO MAXIMISE THE CHANCES OF REACHING THE LIGHT BEFORE FOOD RESERVES ARE EXHAUSTED
• ALL RESOURCES DIVERTED INTO 'VERTICAL' GROWTH
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D + 10 min WW
D
HOW IS LIGHT INVOLVED?
Apical hook unfoldsLeaves expandHypocotyl shows reduced elongation
Only 10 min of white light is sufficient to initiate (or signal) partial de-etiolation
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Is photosynthesis involved in the de-etiolation 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
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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
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LETTUCE SEED GERMINATION
RED RED>FAR-REDDARK
Germination response of lettuce seeds to RED (650-680 nm) and FAR-RED (710-750nm) wavelengths of light
NB: Modern varieties of lettuce are selected NOT to show this response: It is inconvenient for farmers and gardeners!
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http://tinyurl.com/lightbs1003
(or search YouTube – BS1003)
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LETTUCE SEED GERMINATION
• Response of lettuce seeds to RED and FAR-RED
• LIGHT TREATMENT GERMINATION RESPONSE• R +• FR -• R>FR -• R>FR>R +• R>FR>R>FR -• R>FR>R>FR>R +
Germination is promoted by RedFar-red reverses the responseResponse depends on the last light treatment Can operate over multiple cycles > SWITCH
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• HOW DO PLANTS DETECT LIGHT?
• ABSORBING IT VIA PHOTORECEPTOR MOLECULES!
PLANTS MUST BE ABLE TO DETECT
BOTH RED AND FAR-RED LIGHT INDEPENDENTLY
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Chlorophyll absorption spectrum
selective
• Chlorophyll A absorption peaks at 432 nm and 663 nm
• Chlorophyll B absorption peaks at 453 nm and 643 nm
BLUE RED
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• 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 > 1964Richard Vierstra & Peter Quail > 1983
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Pr Pfrred
far red
Phytochromes are reversibly photochromic
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Phytochrome absorption spectrum
FAR-RED
Ab
sorb
an
ce
Wavelength (nm)
666
730
MODEL
PR PFRRED >>>>BIOLOGICAL ACTIVITY
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• 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
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THE PHYTOCHROME MOLECULE
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)
C15
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Slow (some plants)
PHYTOCHROME MODE OF ACTION
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http://tinyurl.com/lightbs1003
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WHERE IS PHYTOCHROME LOCALISED?
• APICAL REGIONS of the root and epicotyl, where most of the dramatic developmental changes occur
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Subcellular localisation of Phytochrome?
• IMMUNOLOCALIZATION: 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)
RED LIGHT
DARK
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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
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Phytochrome regulates growth & development through gene
activation
• CAB = CHLOROPHYLL A/B BINDING PROTEIN
• RUBISCO = (RIBULOSE 1,5-BIS PHOSPHATE CARBOXYLASE-OXYGENASE)
RED PR PFR >>>> BIOLOGICAL ACTIVITY
FAR-RED
MODEL
Gene activation
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A model of phytochrome regulation of rbcS & cab genes
Pr Pfrred
far red
Nucleus
Pfr
PfrPIF
Cell surface
Cytoplasm
Chloroplast
CAB
RBCS
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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
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• 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
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Rafflesia arnoldii
THE TRANSITION TO FLOWERING
1 meter11 kg
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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
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VEGETATIVE VERSUS REPRODUCTIVE GROWTH
Flower development involves a dramatic change in the STRUCTURE and ACTIVITY of
the SHOOT APEX
Vegetative meristem
Leafprimordia
Inflorescence meristem
Flowerprimordia
Floral meristem
Floral organprimordia
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Apical meristem transformations
• Shoot apical meristem
Inflorescence & floral meristems
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• VEGETATIVE SHOOT APEX - simple structure
• 1. LEAF PRIMORDIA EMERGE IN A SPIRAL ARRANGEMENT (PHYLLOTAXY)
• 2. REPETITIVE• 3. INDETERMINATE
SUMMARY
FLORAL APEX - more complex1. SHOOT STOPS ELONGATION GROWTH2. INITIATES MULTIPLE FLORAL ORGANS3. NON-REPETITIVE4. DETERMINATE
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Development of a single flower bud of Arabidopsis
Coordinated growth of different organs
P
P
C
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PLANT AGE LIGHTTEMPERATURE
FACTORS THAT INFLUENCE FLOWERING
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Flowering Signals
• 1. PLANT AGE - JUVENILE TO ADULT FORM
• “RIPENESS-TO-FLOWER”
• eg. Tobacco will only flower after 15-20 nodes
• eg. Many tree species flower only after >10 years
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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
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• Two GENERAL CHARACTERISTICS that could be required for the ability to flower:
• THE CHRONOLOGICAL AGE OF THE PLANT
• THE LARGER SIZE OF THE PLANT
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Century plant(Agave americana)
Botanic GardensUniversity of Leicester
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LATE FLOWERING MUTANTS of Arabidopsis
Both OLD and LARGEBut still flower late
Genetic Control
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2. LIGHT: PHOTOPERIOD
• SECOND MAJOR FACTOR• INFLUENCING THE • 'DECISION' TO FLOWER • IS LIGHT (DAYLENGTH)
• 1. LONG DAY PLANTS
• 2. SHORT DAY PLANTS
• 3. DAY-NEUTRAL PLANTS • eg. tobacco, tomato, sunflower• dandelions, cucumbers, roses,
snapdragons, carnations, cotton
LDP
SDP
Day Neutral
FloweringResponse
Photoperiod(h)
CDL = Critical Daylength
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Poinsettia
KalanchoeSHORT DAY PLANTCoffea arabica SoybeanStrawberryChrysanthemum Christmas cactusDahliasLate summer/autumn
LONG DAY PLANTSWheat/SpinachLettuce/RadishBeet/CloverGladiolus/IrisArabidopsisLate spring/Summer
SHORT DAYS (<8h)
LONG DAYS (>12h)
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WHY USE DAYLENGTH OR OTHER ENVIRONMENTAL SIGNAL?
• PROVIDES A MEANS OF SYNCHRONISING GROWTH AND REPRODUCTION
• - WITH EACH OTHER• - WITH THE ENVIRONMENT
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Harry Allard photoperiod experiments
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LIG H T T R E A T M E N T F L O W E RIN G R E S P O N S E
S D P L D P
Relationship between photoperiod and flowering response
Length of the DARK PERIOD determines the flowering responseIn both SDP & LDP
VegetativeFlower
Vegetative Flower
Vegetative Flower
Vegetative Flower
Promotes flowering in LDP
Day break no effect
Night break inhibits flowering in SDP
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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
RED PR PFR >>>> BIOLOGICAL ACTIVITY
INHIBIT FLOWERINGFAR-RED/DARK
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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 RED PR PFR >>>> BIOLOGICAL ACTIVITY
PROMOTE FLOWERINGFAR-RED/DARK
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• BUT DAYLENGTH CANNOT BE USED TO DISTINGUISH BETWEEN AUTUMN & SPRING
Both have short nights, but very different outcomes!
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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
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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.
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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
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EVIDENCE?
• ‘BAGGING’
• GRAFTING
•
Cocklebur (Xanthium)
SDP
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BAGGING EXPERIMENTS (Cocklebur= SDP)
Bagging of apical leaf on plant grown in LONG DAYS (un-induced) leads to flowering
Signal
LD LD
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GRAFTING EXPERIMENTS (Cocklebur = SDP)
• graft SD-induced leaf onto LD-uninduced stock
induces flowering
repeat cell memory Signal moves
leaf to apex
LD
SD
LD LD
LD LD
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• 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
• (NB: Big change: need post-2010 textbook; Wikipedia is poor!)
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• http://faculty.washington.edu/takato/i.html• http://www.mpipz.mpg.de/25240/coupland_2008_01
_31_part1.pdf• And part 2• And
www2.ju.edu.jo/sites/Academic/tamimi/Material/Fflower.ppt&ei=qPNnUoflDbSg0wWzjYHQCA&usg=AFQjCNGb1dG34gBOdILat7ZfRIcSQQrpag&sig2=Icn04C7ZjwyC0lDjAhbmbg&bvm=bv.55123115,d.d2khttps://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&ved=0CGEQFjAG&url=http%3A%2F%2Fwww2.ju.edu.jo%2Fsites%2FAcademic%2Ftamimi%2FMaterial%2Fflower.ppt&ei=qPNnUoflDbSg0wWzjYHQCA&usg=AFQjCNGb1dG34gBOdILat7ZfRIcSQQrpag&sig2=Icn04C7ZjwyC0lDjAhbmbg&bvm=bv.55123115,d.d2k
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