Chapter 39 Plant Responses to Internal External Stimuli

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

Figure 39. 5 What part of a coleoptile senses light, and how is the signal transmitted? 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. RESULTS Control Boysen-Jensen (1913) Darwin and Darwin (1880) Shaded side of coleoptile Light Illuminated side of coleoptile Tip removed Tip covered by opaque cap Tip covered by transparent cap Base covered by opaque shield Tip separated by gelatin block Tip separated by mica 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. 6 Does asymmetric distribution of a growth-promoting chemical cause a coleoptile to grow toward the light? 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-promoting chemical diffuses into agar block Control (agar block lacking chemical) has no effect Agar block with chemical stimulates growth Offset blocks cause curvature 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.

Chapter 39: Plant Responses to Internal & External Stimuli 1. How was it determined that the plant tip controlled phototropism? 2. 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

Chapter 39: Plant Responses to Internal & External Stimuli 1. How was it determined that the plant tip controlled phototropism? 2. 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

Figure 39. 10 The effect of gibberellin treatment on Thompson seedless grapes

Figure 39. 11 Gibberellins mobilize nutrients during the germination of grain seeds 22 The aleurone responds by synthesizing and secreting digestive enzymes that hydrolyze stored nutrients in the endosperm. One example is -amylase, which hydrolyzes starch. (A similar enzyme in our saliva helps in digesting bread and other starchy foods. ) 1 After a seed imbibes water, the embryo releases gibberellin (GA) as a signal to the aleurone, the thin outer layer of the endosperm. 3 Sugars and other nutrients absorbed from the endosperm by the scutellum (cotyledon) are consumed during growth of the embryo into a seedling. Aleurone Endosperm -amylase GA GA Water Radicle Scutellum (cotyledon) Sugar

Chapter 39: Plant Responses to Internal & External Stimuli 1. How was it determined that the plant tip controlled phototropism? 2. 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

Figure 39. 13 How does ethylene concentration affect the triple response in seedlings? EXPERIMENT Germinating pea seedlings were placed in the dark and exposed to varying ethylene concentrations. Their growth was compared with a control seedling not treated with ethylene. RESULTS All the treated seedlings exhibited the triple response. Response was greater with increased concentration. 0. 00 0. 10 0. 20 0. 40 0. 80 Ethylene concentration (parts per million) CONCLUSION Ethylene induces the triple response in pea seedlings, with increased ethylene concentration causing increased response. Slowing elongation, stem thickening, & stem curvature

Chapter 39: Plant Responses to Internal & External Stimuli 1. How was it determined that the plant tip controlled phototropism? 2. What are the primary plant hormones? 3. How does auxin control cell elongation?

Figure 39. 8 Cell elongation in response to auxin: the acid growth hypothesis Cross-linking cell wall polysaccharides 3 Wedge-shaped expansins, activated by low p. H, separate cellulose microfibrils from cross-linking polysaccharides. The exposed cross-linking polysaccharides are now more accessible to cell wall enzymes. Expansin 4 The enzymatic cleaving of the cross-linking CELL WALL polysaccharides allows the microfibrils to slide. The extensibility of the cell wall is increased. Turgor causes the cell to expand. H 2 O Cell wall enzymes Microfibril H+ 2 The cell wall becomes more acidic. Plasma membrane H+ Cell wall H+ H+ H+ 1 Auxin increases the activity of proton pumps. ATP Cytoplasm Nucleus Vacuole H+ Plasma membrane 5 With the cellulose loosened, the cell can elongate.

Chapter 39: Plant Responses to Internal & External Stimuli 1. 2. 3. 4. 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

Figure 39. 16 Abscission of a maple leaf 0. 5 mm - Aging leaves produce less auxin so abscission layer is more sensitive to ethylene - Abscission layer has thin walls - Weight of leaf causes separation Protective layer Abscission layer Stem Petiole

Chapter 39: Plant Responses to Internal & External Stimuli 1. 2. 3. 4. 5. 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 6. How are plants able to respond to light? - Blue-light photoreceptors - Phytochromes

Figure 39. 17 What wavelengths stimulate phototropic bending toward light? EXPERIMENT 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. Phototropic effectiveness relative to 436 nm RESULTS The graph below shows phototropic effectiveness (curvature per photon) relative to 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. 1. 0 0. 8 0. 6 0. 4 0. 2 0 400 450 500 550 600 650 700 Wavelength (nm) Light Time = 0 min. Time = 90 min. CONCLUSION The phototropic bending toward light is caused by a photoreceptor that is sensitive to blue and violet light, particularly blue light.

Figure 39. 19 Structure of a phytochrome 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. 2 Light-induced de-etiolation (greening) of dark-grown potatoes (a) Before exposure to light. A dark-grown potato has tall, spindly stems and nonexpanded leaves—morphological adaptations that enable the shoots to penetrate the soil. The roots are short, but there is little need for water absorption because little water is lost by the shoots. (b) After a week’s exposure to natural daylight. The potato plant begins to resemble a typical plant with broad green leaves, short sturdy stems, and long roots. This transformation begins with the reception of light by a specific pigment, phytochrome.

Figure 39. 4 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response 2 Transduction 1 Reception 3 Response CYTOPLASM Plasma membrane NUCLEUS c. GMP Second messenger produced Phytochrome activated by light Cell wall Light Specific protein kinase 1 activated

Figure 39. 4 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response 2 Transduction 1 Reception 3 Response CYTOPLASM NUCLEUS c. GMP Plasma membrane Second messenger produced Specific protein kinase 1 activated Phytochrome activated by light Cell wall Specific protein kinase 2 activated Light Ca 2+ channel opened Ca 2+

Figure 39. 4 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response 2 Transduction 1 Reception 3 Response Transcription factor 1 NUCLEUS CYTOPLASM c. GMP Plasma membrane Second messenger produced Specific protein kinase 1 activated Phytochrome activated by light P Transcription factor 2 P Cell wall Specific protein kinase 2 activated Transcription Light Translation Ca 2+ channel opened Ca 2+ De-etiolation (greening) response proteins

Red light Pr 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 Pfr Far-red light

Figure 39. 20 Phytochrome: a molecular switching mechanism Pr Pfr Red light Responses: seed germination, control of flowering, etc. Synthesis Far-red light Slow conversion in darkness (some plants) Enzymatic destruction

Figure 39. 18 How does the order of red and far-red illumination affect seed germination? EXPERIMENT During the 1930 s, 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. RESULTS 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 exposed to red light (left). Germination was inhibited in groups of seeds that were last exposed to far-red light (right). Dark (control) Red Dark Red Far-red Dark Red Far-red CONCLUSION 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.

Chapter 39: Plant Responses to Internal & External Stimuli 1. 2. 3. 4. 5. 6. 7. 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

Figure 39. 22 How does interrupting the dark period with a brief exposure to light affect flowering? EXPERIMENT During the 1940 s, researchers conducted experiments in which periods of darkness were interrupted with brief exposure to light to test how the light and dark portions of a photoperiod affected flowering in “short-day” and “long-day” plants. RESULTS 24 hours Darkness Day neutral plants are unaffected by photoperiod…. maturity important. Flash of light Critical dark period Light (a) “Short-day” plants flowered only if a period of continuous darkness was longer than a critical dark period for that particular species (13 hours in this example). A period of darkness can be ended by a brief exposure to light. (b) “Long-day” plants flowered only if a period of continuous darkness was shorter than a critical dark period for that particular species (13 hours in this example). CONCLUSION The experiments indicated that flowering of each species was determined by 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.

Figure 39. 23 Is phytochrome the pigment that measures the interruption of dark periods in photoperiodic response? EXPERIMENT 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. 24 20 R FR R Hours 16 R FR R Critical dark period RESULTS 12 8 4 0 Short-day (long-night) plant Long-day (short-night) plant CONCLUSION 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 was canceled. This reversibility indicated that it is phytochrome that measures the interruption of dark periods.

Figure 39. 24 Is there a flowering hormone? EXPERIMENT To test whethere is a flowering hormone, researchers conducted an experiment in which a plant that had been induced to flower by photoperiod was grafted to a plant that had not been induced. RESULTS Plant subjected to photoperiod that does not induce flowering Plant subjected to photoperiod that induces flowering Graft Time (several weeks) YES!!! Florigen – flowering signal CONCLUSION Both plants flowered, indicating the transmission of a flower-inducing substance. In some cases, the transmission worked even if one was a short-day plant and the other was a long-day plant.

Chapter 39: Plant Responses to Internal & External Stimuli 1. 2. 3. 4. 5. 6. 7. 8. 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

Figure 39. 25 Positive gravitropism in roots: the statolith hypothesis Statoliths (a) (b) 20 m

Chapter 39: Plant Responses to Internal & External Stimuli 1. 2. 3. 4. 5. 6. 7. 8. 9. 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

Figure 39. 26 Altering gene expression by touch in Arabidopsis

Figure 39. 27 Rapid turgor movements by the sensitive plant (Mimosa pudica) (a) Unstimulated (b) Stimulated Side of pulvinus with flaccid cells Leaflets after stimulation Side of pulvinus with turgid cells Pulvinus (motor organ) (c) Motor organs Vein 0. 5 m

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. )

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.

FRQ #2 • • • Evaporative pull (negative pressure) Water potential- high low Stomata details Xylem details Cohesion/adhesion/hydrogen bonds • Adaptations (x 2): – Small leaf surface area – Thick cuticle – Fewer open stomata (CAM/C 4) – Dormancy/lose leaves

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

FRQ #3 • A) 1 pt: ID Graph A—bacteriorhodopson & Graph B— chlorophyll a • 2 pts: 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)

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

AP Test Info • First week of exams (May 4 -8)… – AP Biology is cancelled on Monday, May 4 th. – We will meet at normal class times on May 5 th-8 th. Attendance is mandatory (unless you are taking an AP exam that morning/afternoon…we will be conducting important review!!!) • AP Bio Exam: Monday, May 11 th • Check-in at 7: 15 am LOCATION LAST NAMES TEST ADMIN S 111 -S 113 A-E Newsome N 213 -N 214 F-La Ferrell S 010 -S 012 Le-R Smith S 215 S-Th Walsh S 213 Ti-Z G. Scott

Friday, May 8 th • 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

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

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

Thursday, April 30 th • 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!)

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

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

AP Bio Letter 1) What does the student need to do in order to succeed in AP Bio? Be specific—test-taking, L. logs, labs, study strategies, etc. 2) How is AP Bio different from other AP classes? 3) General tips for success/words of encouragement 4) Sign your name, home high school, and college (if a senior. )

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

• 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 Power. School! – – 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.

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 Power. Points – on website

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