Chapter 39: Plant Responses to Internal & External Stimuli

1. Chapter 39: Plant Responses to Internal & External Stimuli 1. How was it determined that the plant tip controlled phototropism?

2. EXPERIMENT In 1880, Charles Darwin and his son Francis designed an experiment to determine what part of the coleoptile senses light. In 1913, Peter Boysen-Jensen conducted an experiment to determine how the signal for phototropism is transmitted. Boysen-Jensen (1913) Control Darwin and Darwin (1880) Shaded side of coleoptile Light RESULTS Light Light Base covered by opaqueshield Tip separated by gelatinblock Tip separated by mica Illuminated side of coleoptile Tip removed Tip covered by opaque cap Tip covered by trans-parentcap CONCLUSION In the Darwins’ experiment, a phototropic response occurred only when light could reach the tip of coleoptile. Therefore, they concluded that only the tip senses light. Boysen-Jensen observed that a phototropic response occurred if the tip was separated by a permeable barrier (gelatin)but not if separated by an impermeable solid barrier (a mineral called mica). These results suggested that the signal is a light-activated mobile chemical. Figure 39.5 What part of a coleoptile senses light, and how is the signal transmitted?

3. EXPERIMENT In 1926, Frits Went’s experiment identified how a growth-promoting chemical causes a coleoptile to grow toward light. He placed coleoptiles in the dark and removed their tips, putting some tips on agar blocks that he predicted would absorb the chemical. On a control coleoptile, he placed a block that lacked the chemical. On others,he placed blocks containing the chemical, either centered on top of the coleoptile to distribute the chemical evenly or offset to increase the concentration on one side. RESULTS The coleoptile grew straight if the chemical was distributed evenly. If the chemical was distributed unevenly, the coleoptile curved away from the side with the block, as if growing toward light, even though it was grown in the dark. Excised tip placed on agar block Growth-promotingchemical diffusesinto agar block Agar blockwith chemicalstimulates growth Control(agar blocklackingchemical)has noeffect Offset blockscause curvature Control CONCLUSION Went concluded that a coleoptile curved toward light because its dark side had a higher concentration of the growth-promoting chemical, which he named auxin. Figure 39.6 Does asymmetric distribution of a growth-promoting chemical cause a coleoptile to grow toward the light? EXPERIMENT

4. Chapter 39: Plant Responses to Internal & External Stimuli • How was it determined that the plant tip controlled phototropism? • What are the primary plant hormones? • Hormone Site of Production Effect • Auxin (IAA) embryo of seed germination • apical meristems apical dominance • Cytokinins roots stimulates cell division • & growth, delays aging

5. Chapter 39: Plant Responses to Internal & External Stimuli • How was it determined that the plant tip controlled phototropism? • What are the primary plant hormones? • Hormone Site of Production Effect • Auxin (IAA) embryo of seed germination • apical meristems apical dominance • Cytokinins roots stimulates cell division • & growth, delays aging • Gibberellins apical meristems elongation & • differentiation, flowering • fruit development • embryo seed germination

6. Figure 39.10 The effect of gibberellin treatment on Thompson seedless grapes

7. 2The aleurone responds by synthesizing and secreting digestive enzymes thathydrolyze stored nutrients inthe endosperm. One exampleis -amylase, which hydrolyzes starch. (A similar enzyme inour saliva helps in digestingbread and other starchy foods.) 1 After a seedimbibes water, theembryo releasesgibberellin (GA) as a signal to thealeurone, the thinouter layer of theendosperm. 3 Sugars and other nutrients absorbedfrom the endospermby the scutellum (cotyledon) are consumed during growth of the embryo into a seedling. Aleurone Endosperm -amylase Sugar GA GA Water Radicle Scutellum (cotyledon) Figure 39.11 Gibberellins mobilize nutrients during the germination of grain seeds 2

8. Chapter 39: Plant Responses to Internal & External Stimuli • How was it determined that the plant tip controlled phototropism? • What are the primary plant hormones? • Hormone Site of Production Effect • Auxin (IAA) embryo of seed germination • apical meristems apical dominance • Cytokinins roots stimulates cell division • & growth, delays aging • Gibberellins apical meristems elongation & • differentiation, flowering • fruit development • embryo seed germination • Abscisic acid leaves, stems, roots, inhibits growth • green fruit prepares for winter • Ethylene ripening fruit ripens fruit • triple response

9. Germinating pea seedlings were placed in the dark and exposed to varying ethylene concentrations. Their growthwas compared with a control seedling not treated with ethylene. EXPERIMENT All the treated seedlings exhibited the tripleresponse. Response was greater with increased concentration. RESULTS 0.10 0.40 0.00 0.20 0.80 Ethylene concentration (parts per million) Ethylene induces the triple response in pea seedlings,with increased ethylene concentration causing increased response. CONCLUSION Figure 39.13 How does ethylene concentration affect the triple response in seedlings? Slowing elongation, stem thickening, & stem curvature

10. Chapter 39: Plant Responses to Internal & External Stimuli • How was it determined that the plant tip controlled phototropism? • What are the primary plant hormones? • How does auxin control cell elongation?

11. 3 Wedge-shaped expansins, activated by low pH, separate cellulose microfibrils from cross-linking polysaccharides. The exposed cross-linking polysaccharides are now more accessible to cell wall enzymes. Cell wallenzymes Expansin Cross-linkingcell wallpolysaccharides 4 The enzymatic cleavingof the cross-linking polysaccharides allowsthe microfibrils to slide.The extensibility of thecell wall is increased. Turgorcauses the cell to expand. CELL WALL Microfibril H2O Cell wall Plasma membrane H+ H+ 2 The cell wallbecomes moreacidic. H+ H+ H+ H+ H+ H+ 1 Auxinincreases theactivity ofproton pumps. Cytoplasm Nucleus Vacuole ATP Plasma membrane H+ 5 With the cellulose loosened, the cell can elongate. Figure 39.8 Cell elongation in response to auxin: the acid growth hypothesis

12. Chapter 39: Plant Responses to Internal & External Stimuli • How was it determined that the plant tip controlled phototropism? • What are the primary plant hormones? • How does auxin control cell elongation? • Why do leaves change colors & fall off trees? • Some pigments made in higher concentrations during fall • (yellow & orange carotenoids, red pigment) • Chlorophyll no longer produced

13. 0.5 mm Abscission layer Protective layer Stem Petiole Figure 39.16 Abscission of a maple leaf • Aging leaves produce less auxin so • abscission layer is more sensitive to ethylene • Abscission layer has thin walls • Weight of leaf causes separation

14. Chapter 39: Plant Responses to Internal & External Stimuli • How was it determined that the plant tip controlled phototropism? • What are the primary plant hormones? • How does auxin control cell elongation? • Why do leaves change colors & fall off trees? • How do plants “move?” • Tropisms – toward or away from stimuli • Photo – light • Gravi – gravity • Thigmo – touch • Turgor movements – changes in turgor pressure in specialized cells • How are plants able to respond to light? • Blue-light photoreceptors • Phytochromes

15. 1.0 0.8 0.6 Phototropic effectiveness relative to 436 nm 0.4 0.2 0 450 500 550 600 650 700 400 Wavelength (nm) Light Time = 0 min. Time = 90 min. Figure 39.17 What wavelengths stimulate phototropic bending toward light? Researchers exposed maize (Zea mays) coleoptiles to violet, blue, green, yellow, orange, and red light to test which wavelengths stimulate the phototropic bending toward light. EXPERIMENT The graph below shows phototropic effectiveness (curvature per photon) relativeto effectiveness of light with a wavelength of 436 nm. The photo collages show coleoptiles before and after 90-minute exposure to side lighting of the indicated colors. Pronounced curvature occurred only with wavelengths below 500 nm and was greatest with blue light. RESULTS CONCLUSION The phototropic bending toward light is caused by a photoreceptor that is sensitive to blue and violet light, particularly blue light.

16. A phytochrome consists of two identical proteins joined to form one functional molecule. Each of these proteins has two domains. Chromophore Photoreceptor activity. One domain, which functions as the photoreceptor, is covalently bonded to a nonprotein pigment, or chromophore. Kinase activity. The other domain has protein kinase activity. The photoreceptor domains interact with the kinase domains to link light reception to cellular responses triggered by the kinase. Figure 39.19 Structure of a phytochrome

17. Figure 39.2 Light-induced de-etiolation (greening) of dark-grown potatoes (a) Before exposure to light. Adark-grown potato has tall,spindly stems and nonexpandedleaves—morphologicaladaptations that enable theshoots to penetrate the soil. Theroots are short, but there is littleneed for water absorptionbecause little water is lost by theshoots. (b) After a week’s exposure tonatural daylight. The potatoplant begins to resemble a typical plant with broad greenleaves, short sturdy stems, andlong roots. This transformationbegins with the reception oflight by a specific pigment,phytochrome.

18. CYTOPLASM NUCLEUS Specific protein kinase 1 activated cGMP Plasma membrane 3 Response 1 Reception 2 Transduction Second messenger produced Phytochrome activated by light Cell wall Light Figure 39.4 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response

19. CYTOPLASM NUCLEUS Specific protein kinase 1 activated cGMP Plasma membrane 3 Response 1 Reception 2 Transduction Second messenger produced Phytochrome activated by light Cell wall Specific protein kinase 2 activated Light Ca2+ channel opened Ca2+ Figure 39.4 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response

20. Transcription factor 1 CYTOPLASM NUCLEUS Specific protein kinase 1 activated cGMP Plasma membrane P 3 Response 1 Reception 2 Transduction Second messenger produced Transcriptionfactor 2 Phytochrome activated by light P Cell wall Specific protein kinase 2 activated Transcription Light Translation De-etiolation (greening) response proteins Ca2+ channel opened Ca2+ Figure 39.4 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response

21. Red light Pfr Pr Far-red light • Phytochromes are sensitive to 2 different wavelengths • Red light converts the phytochrome to be far-red sensitive • Far-red converts the phytochrome to be red light sensitve

22. Synthesis Figure 39.20 Phytochrome: a molecular switching mechanism Pr Pfr Red light Responses: seed germination, control of flowering, etc. Far-red light Slow conversion in darkness (some plants) Enzymatic destruction

23. Dark (control) Red Dark Far-red Dark Red Far-red Dark Red Red Red Far-red Red Far-red Figure 39.18 How does the order of red and far-red illumination affect seed germination? During the 1930s, USDA scientists briefly exposed batches of lettuce seeds to red light or far-red light to test the effects on germination. After the light exposure, the seeds were placed in the dark, and the results were compared with control seeds that were not exposed to light. EXPERIMENT The bar below each photo indicates the sequence of red-light exposure, far-red light exposure, and darkness. The germination rate increased greatly in groups of seeds that were last exposedto red light (left). Germination was inhibited in groups of seeds that were last exposed to far-red light (right). RESULTS Red light stimulated germination, and far-red light inhibited germination.The final exposure was the determining factor. The effects of red and far-red light were reversible. CONCLUSION

24. Chapter 39: Plant Responses to Internal & External Stimuli • How was it determined that the plant tip controlled phototropism? • What are the primary plant hormones? • How does auxin control cell elongation? • Why do leaves change colors & fall off trees? • How do plants “move?” • How are plants able to respond to light? • What controls a plant’s biological clock? • Photoperiodism – a physiological response to the duration of night & day • Flowering

25. During the 1940s, researchers conducted experiments in which periods of darkness were interrupted with brief exposure to light to test how the light and dark portionsof a photoperiod affected flowering in “short-day” and “long-day” plants. EXPERIMENT RESULTS Darkness Flash oflight 24 hours Criticaldarkperiod Light (a) “Short-day” plantsflowered only if a period ofcontinuous darkness waslonger than a critical darkperiod for that particularspecies (13 hours in thisexample). A period ofdarkness can be ended by abrief exposure to light. (b) “Long-day” plantsflowered only if aperiod of continuousdarkness was shorterthan a critical darkperiod for thatparticular species (13hours in this example). The experiments indicated that flowering of each species was determinedby a critical period of darkness (“critical night length”) for that species, not by a specific period of light. Therefore, “short-day” plants are more properly called “long-night” plants, and “long-day”plants are really “short-night” plants. CONCLUSION Figure 39.22 How does interrupting the dark period with a brief exposure to light affect flowering? Day neutral plants are unaffected by photoperiod….maturity important.

26. A unique characteristic of phytochrome is reversibility in response to red and far-red light. To test whether phytochrome is the pigment measuring interruption of dark periods, researchers observed how flashes of red light and far-red light affected flowering in “short-day” and “long-day” plants. EXPERIMENT RESULTS 24 FR R 20 R FR FR FR Critical dark period R R R R 16 Hours 12 8 4 0 Short-day (long-night) plant Long-day (short-night) plant A flash of red light shortened the dark period. A subsequent flash of far-red light canceled the red light’s effect. If a red flash followed a far-red flash, the effect of the far-red light wascanceled. This reversibility indicated that it is phytochrome that measures the interruption of dark periods. CONCLUSION Figure 39.23 Is phytochrome the pigment that measures the interruption of dark periods in photoperiodic response?

27. To test whether there is a flowering hormone, researchers conducted an experiment in which a plant that had been induced to flower by photoperiod was grafted toa plant that had not been induced. EXPERIMENT RESULTS Plant subjected to photoperiod that does not induce flowering Plant subjected to photoperiod that induces flowering Graft Time(severalweeks) Both plants flowered, indicating the transmission of a flower-inducingsubstance. In some cases, the transmission worked even if one was a short-day plantand the other was a long-day plant. CONCLUSION Figure 39.24 Is there a flowering hormone? YES!!! Florigen – flowering signal

28. Chapter 39: Plant Responses to Internal & External Stimuli • How was it determined that the plant tip controlled phototropism? • What are the primary plant hormones? • How does auxin control cell elongation? • Why do leaves change colors & fall off trees? • How do plants “move?” • How are plants able to respond to light? • What controls a plant’s biological clock? • How does gravitropism work? • - Statoliths

29. Statoliths 20 m (a) (b) Figure 39.25 Positive gravitropism in roots: the statolith hypothesis

30. Chapter 39: Plant Responses to Internal & External Stimuli • How was it determined that the plant tip controlled phototropism? • What are the primary plant hormones? • How does auxin control cell elongation? • Why do leaves change colors & fall off trees? • How do plants “move?” • How are plants able to respond to light? • What controls a plant’s biological clock? • How does gravitropism work? • What’s the difference between thigmomorphogenesis & thigmotropism? • Thigmomorpho – permanent change in shape (p 1087) • Thigmo – growth in response to touch - vines

31. Figure 39.26 Altering gene expression by touch in Arabidopsis

32. (a) Unstimulated (b) Stimulated Side of pulvinus with flaccid cells Leafletsafterstimulation Side of pulvinus with turgid cells Pulvinus(motororgan) Vein (c) Motor organs 0.5 m Figure 39.27 Rapid turgor movements by the sensitive plant (Mimosa pudica)

33. Unit 10 Test • 1) Please put your Learning Logs in the bin by the door. Take a scantron from the pile by the bin. • 2) Please use the BLUE SIDE of the scantron and mark your test version (A or B) on your scantron! • Also, write your name on everything except the ‘green sheet.’ • 3) If you have food, please place it on the floor by the computer table and sign the food log. Thank you! (Food is due by Friday…if you already donated 6 cans for the Animal Test, you do not need to do anything else this time.)

34. Agenda for today… • 1) Pick up your graded learning log from the table by the door. • 2) Plant test stats: • AVG: 13 out of 18 • RANGE: 6 – 18 • Most missed: A #7/B #10; #17 • Test corrections are due on THURSDAY. • 3) Don’t forget: PHOTOSYNTHESIS LAB—due THURSDAY • 4) AP Exam “Bubbling” and review. • IF YOU WERE ABSENT YESTERDAY AND HAVEN’T YET TAKEN THE PLANT TEST, SEE ME TO SCHEDULE A TIME FOR TODAY OR TOMORROW.

35. FRQ #2 • Evaporative pull (negative pressure) • Water potential- high  low • Stomata details • Xylem details • Cohesion/adhesion/hydrogen bonds • Adaptations (x2): • Small leaf surface area • Thick cuticle • Fewer open stomata (CAM/C4) • Dormancy/lose leaves

36. FRQ #1 • Pollen tube elongates down carpel/style • Sperm #1 fertilizes egg  diploid zygote • Sperm #2 joins with polar nuclei  triploid endosperm • Genetic • S-gene • Self-incompatibility (w/ description) • Mechanical • Pin & thrum flowers • Stamen/carpel located at slightly different heights • Temporal • Sperm/egg mature at slightly different times

37. FRQ #3 • A) 1pt: ID Graph A—bacteriorhodopson & Graph B—chlorophyll a • 2pts: Explain that the an organism w/ bacteriorhodopsin appears purple b/c it doesn’t absorb purple light AND that an organism w/ chlorophyll appears green b/c it doesn’t absorb green light • B) Highest: 430 nm (b/c most absorption = most energy available for photosynthesis) • Intermediate: 650 nm (b/c …) • Lowest: 550 nm (b/c least absorption = least energy available for photosynthesis)

38. AP Exam Prep • Take one of each of the following from the table by the door: • Practice exam answer chart • AP Biology Formula Sheet • Math Practice Packet

39. AP Test Info • First week of exams (May 4-8)… • AP Biology is cancelled on Monday, May 4th. • We will meet at normal class times on May 5th-8th. Attendance is mandatory (unless you are taking an AP exam that morning/afternoon…we will be conducting important review!!!) • AP Bio Exam: Monday, May 11th • Check-in at 7:15am

40. Friday, May 8th • Options for today—YOUR VOTE: • 1) Continue work on FRQs • 2) Use 2014 AP Bio exam to do “mini-test” • 17 M.C. ?s and 5 Math ?s • 3) Math Practice Packet

41. Post-AP Bio Exam Schedule • Tue., May 12 • Periods 1-4 cancelled • Periods 6, 8 will meet • Wed., May 13 • Periods 1-4 cancelled • Periods 6, 8 will meet • Thu., May 14 • ALL periods will meet • Fri., May 15 • ALL periods will meet

42. Test Day Prep… • 1) If you have questions, come to Saturday, May 9th review • 8am-3pm • 2) Get plenty of sleep on Sunday night!!! • 3) On Monday…be at your testing room at 7:15am with: • #2 pencils, black pens • Approved calculator • Photo ID • AP Student Pack w/ sticker labels

43. Thursday, April 30th • 1) Please staple test corrections to multiple-choice sheet and place them in the appropriate file. • 2) Put your lab notebooks in the blue bin. • 3) TOMORROW: MEET IN MR. BENNETT’S ROOM FOR DR. ANDERSON’S REVIEW LECTURE ON BEHAVIOR, GENETICS, HORMONES, EVOLUTION, ETC. (Please be attentive, respectful, and inquisitive!)

44. Thursday, May 14th • 1) Turn in your test folder! • 2) Donate your calculator?

45. 4th quarter grades… • Learning Objective PPT projects are graded in ALL periods. • Photosynthesis Labs are graded in 4th, 6th, & 8th periods. • Overall grade is totally updated in those classes and reflects a “floor” for your 4th quarter grade, assuming that you attend class as expected and submit complete classwork assignments through May 27th.

46. AP Bio Letter • What does the student need to do in order to succeed in AP Bio?  Be specific—test-taking, L. logs, labs, study strategies, etc. • How is AP Bio different from other AP classes? • General tips for success/words of encouragement • Sign your name, home high school, and college (if a senior.)

47. AP Biology “Taboo” Units • Ch. 2-5 Group 1 • Ch. 6-12 Group 2 • Ch. 13-17 Group 3 • Ch. 18-21 Group 4 • Ch. 22-26 Group 5 • Ch. 50-55 Group 6 • Ch. 40, 43, 45, 48 Group 7 • Ch. 36-39 Group 8

48. 1) L.O. projects are due to me (emailed) by midnight tonight. Refer to your instructions for emailing instructions. • 2) Plant Test FRQs are graded. We’ll review them in-class on Tuesday. Final Plant Test grades are now in PowerSchool! • TUESDAY: 1) Review Plant FRQs • 2) Review M.C./Math Practice that you did today • 3) Review “Math Practice Packet”—Look at it this weekend! • 4) Begin AP Exam FRQ review (continued on Wed, Thu, Fri) • 3) Please get out your Practice AP Exam answer grid, AP Math Formula Sheet, and calculator…we’re finishing multiple-choice & math today.

49. CALCULATORS??? • -Options to Prepare • -Practice exam MC – answers will be available in folder • -2013 FRQ – rubric available in folder • -Math practice – answers on-line • -Q&A – with me • -Review figures throughout book – practice interpreting info • -Review videos/animations on my website (Bozeman, etc.) • -Review old tests • -Review projects • -Review Chapter PowerPoints – on website

50. Final Exam • 1) Be sure you’re aware of the correct date/time for your exam. • 2) 5 cans = 5 points; due on Test Day • No transport opportunity unless you speak with me directly • 3) 100 M.C. questions…bring “approved” calculator