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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. …

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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  • 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
  • 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. In the absence of light we see: ETIOLATION LONG HYPOCOTYL REDUCED LEAF EXPANSION APICAL HOOK PALE IN COLOUR Photomorphogenesis Etiolation or Skotomorphogenesis
  • 21. skoto- & photomorphogenesis in potato DE-ETIOLATION IS DRAMATIC Developmental response to the light signal!
  • 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. 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. 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. 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. 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. http://tinyurl.com/lightbs1003 (or search YouTube – BS1003)
  • 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. PLANTS MUST BE ABLE TO DETECT BOTH RED AND FAR-RED LIGHT INDEPENDENTLY • HOW DO PLANTS DETECT LIGHT? • ABSORBING IT VIA PHOTORECEPTOR MOLECULES!
  • 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. • 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. Pr red far red Pfr Phytochromes are reversibly photochromic
  • 33. Phytochrome absorption spectrum Absorbance 666 MODEL PR RED FAR-RED 730 Wavelength (nm) PFR >>>> BIOLOGICAL ACTIVITY
  • 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. 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. PHYTOCHROME MODE OF ACTION Slow (some plants)
  • 37. http://tinyurl.com/lightbs1003
  • 38. WHERE IS PHYTOCHROME LOCALISED? • APICAL REGIONS of the root and epicotyl, where most of the dramatic developmental changes occur
  • 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. 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. 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. 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. 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. • 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. THE TRANSITION TO FLOWERING 1 meter 11 kg Rafflesia arnoldii
  • 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. 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. Apical meristem transformations • Shoot apical Inflorescence & floral meristems
  • 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. Development of a single flower bud of Arabidopsis Coordinated growth of different organs P P C
  • 51. FACTORS THAT INFLUENCE FLOWERING PLANT AGE LIGHT TEMPERATURE
  • 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. 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. • 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. Century plant (Agave americana) Botanic Gardens University of Leicester
  • 56. LATE FLOWERING MUTANTS of Arabidopsis Both OLD and LARGE But still flower late Genetic Control
  • 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. 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. WHY USE DAYLENGTH OR OTHER ENVIRONMENTAL SIGNAL? • PROVIDES A MEANS OF SYNCHRONISING GROWTH AND REPRODUCTION • • - WITH EACH OTHER - WITH THE ENVIRONMENT
  • 60. Harry Allard photoperiod experiments
  • 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. 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. 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. • BUT DAYLENGTH CANNOT BE USED TO DISTINGUISH BETWEEN AUTUMN & SPRING Both have short nights, but very different outcomes!
  • 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. 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. 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. EVIDENCE? • ‘BAGGING’ • GRAFTING • SDP Cocklebur (Xanthium)
  • 69. BAGGING EXPERIMENTS (Cocklebur= SDP) Signal LD LD Bagging of apical leaf on plant grown in LONG DAYS (un-induced) leads to flowering
  • 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. • 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. • 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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