1. BIOLOGY CONCEPTS & CONNECTIONS Fourth Edition Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor From PowerPoint ® Lectures for Biology: Concepts & Connections CHAPTER 33 Control Systems in Plants Modules 33.1 – 33.5

2. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Soy offers many dietary benefits –It is one of the few plant proteins that contains all the essential amino acids, making it a healthy substitute for meat –It may reduce the risk of heart disease Examples of soy products include soy milk, tofu, soy flour, and miso The Benefits of Soy

3. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Soy also contains non-nutritive phytochemicals –These may have significant metabolic effects on the human body Plants, like humans, use hormones as chemical signals that control growth and development When we consume plants, we consume plant hormones

4. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phytoestrogen is a plant hormone found in soy –Its chemical structure is similar to that of the human sex hormone estrogen Estrogen (Estradiol)Phytoestrogen (Genistein)

5. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Isoflavones are one type of phytoestrogen found in soy –Menopausal women often choose dietary supplements with isoflavones over hormone replacement therapy –But scientists have not established the benefits and risks of isolated isoflavones

6. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hormones coordinate the activities of plant cells and tissues The study of plant hormones began with observations of plants bending toward light –This phenomenon is called phototropism 33.1 Experiments on how plants turn toward light led to the discovery of a plant hormone PLANT HORMONES Figure 33.1A

7. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phototropism results from faster cell growth on the shaded side of the shoot than on the illuminated side Figure 33.1B Shaded side of shoot Light Illuminated side of shoot

8. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Experiments carried out by Darwin and others showed that the tip of a grass seedling detects light and transmits a signal down to the growing region of the shoot Figure 33.1C Light ControlTip removed DARWIN AND DARWIN (1880)BOYSEN-JENSEN (1913) Tip covered by opaque cap Tip covered by trans- parent cap Base covered by opaque shield Tip separated by gelatin block Tip separated by mica

9. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings It was discovered in the 1920s that a hormone was responsible for the signaling Darwin observed –This hormone was dubbed auxin –Auxin plays an important role in phototropism

10. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 33.1D Shoot tip placed on agar block. Chemical (later called auxin) diffuses from shoot tip into agar. Agar Control NO LIGHT Block with chemical stimulates growth. Offset blocks with chemical stimulate curved growth. Other controls: Blocks with no chemical have no effect.

11. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hormones regulate plant growth and development by affecting –cell division –cell elongation –cell differentiation Only small amounts of hormones are necessary to trigger the signal-transduction pathways that regulate plant growth and development 33.2 Five major types of hormones regulate plant growth and development

12. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Table 33.2

13. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plants produce auxin (IAA) in the apical meristems at the tips of shoots –At different concentrations, auxin stimulates or inhibits the elongation of shoots and roots Figure 33.3B STEMS ROOTS 0.9 g/L

14. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The effect of auxin on pea plants Figure 33.3A

15. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Auxin may initiate elongation by weakening cell walls Figure 33.3C Plasma membrane Cell wall Vacuole Auxin stimulates H + pump (protein) H+H+ CYTOPLASM Cellulose molecule H+H+ CELL WALL Activates Enzyme Cellulose loosens; cell can elongate CELL ELONGATION H2OH2O

16. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Auxin stimulates cell division and the development of vascular tissues in vascular cambium –This promotes growth in stem diameter

17. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cytokinins are hormones that promote cell division –They are produced in actively growing roots, embryos, and fruits The antagonistic interaction of auxin and cytokinin may be one way a plant coordinates the growth of its root and shoot systems 33.4 Cytokinins stimulate cell division

18. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Cytokinins from roots may balance the effects of auxin from apical meristems, causing lower buds to develop into branches –The basil plant on the right has had its terminal bud removed –The inhibitory effect of auxin on axillary buds was thus eliminated –Cytokinins from the roots activated the axillary buds, making the plant grow more branches Terminal bud No terminal bud Figure 33.4

19. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gibberellins stimulate cell elongation and cell division in stems and leaves –Foolish seedling disease occurs when rice plants infected with the Gibberella fungus get an overdose of gibberellin 33.5 Gibberellins affect stem elongation and have numerous other effects Figure 33.5A

20. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gibberellins, in combination with auxin, can influence fruit development –Gibberellins can make grapes grow larger and farther apart in a cluster –The grapes at right were treated with gibberellin, while those at left were not Figure 33.5B

21. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gibberellin-auxin sprays can make apples, currants, and eggplants develop without fertilization Gibberellins released from embryos function in some of the early events of seed germination

22. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Abscisic acid (ABA) inhibits the germination of seeds The ratio of ABA to gibberellins often determines whether a seed will remain dormant or will germinate 33.6 Abscisic acid inhibits many plant processes

23. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Seeds of many plants remain dormant until their ABA is inactivated or washed away –These flowers grew from seeds that germinated after a rainstorm in the Mojave Desert Figure 33.6

24. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings ABA also acts as a “stress hormone” –It causes stomata to close when a plant is dehydrated –Thus the rate of transpiration is decreased and further water loss prevented

25. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ethylene is a gaseous hormone that triggers fruit ripening Ethylene is given off as cells age These bananas were exposed to different amounts of ethylene over the same time period 33.7 Ethylene triggers fruit ripening and other aging processes Figure 33.7A

26. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Fruit growers use ethylene to control ripening –Apple farmers take measures to retard the ripening action of natural ethylene –Tomato farmers pick unripe fruit and then pipe ethylene into storage bins to promote ripening

27. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The shorter days of autumn trigger a changing ratio of auxin to ethylene –This is the likely cause of the changes seen in deciduous trees — color changes, drying, and the loss of leaves Figure 33.7B Leaf stalk Stem (twig) Protective layer Abscission layer StemLeaf stalk

28. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plant hormones have a variety of agricultural uses –Farmers use auxin to delay or promote fruit drop –Auxin and gibberellins are used to produce seedless fruits –A synthetic auxin (2,4-D) is used to kill weeds 33.8 Connection: Plant hormones have many agricultural uses

29. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings There are many questions and concerns about the safety of using such chemicals in food production Figure 33.8

30. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plants sense and respond to environmental changes in a variety of ways Tropisms are growth responses that change the shape of a plant or make it grow toward or away from a stimulus 33.9 Tropisms orient plant growth toward or away from environmental stimuli GROWTH RESPONSES AND BIOLOGICAL RHYTHMS IN PLANTS

31. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Phototropism is the bending toward light –It may result from auxin moving from the illuminated side to the shaded side of a stem Figure 33.1A

32. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gravitropism is a response to gravity –It may be caused by the settling of special organelles on the low sides of shoots and roots –This may trigger a change in the distribution of hormones Figure 33.9A

33. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Gravitropism is an important adaptation –It ensures that the shoot will grow upward toward light and the roots will grow down into the soil, no matter how the seed lands in the soil

34. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Thigmotropism is a response to touch –It is responsible for the coiling of tendrils and vines around objects –It enables plants to use other objects for support while growing toward sunlight Figure 33.9B

35. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plants possess an internal biological clock that controls daily cycles These cycles are called circadian rhythms –Even in the absence of environmental cues, they persist with periods of about 24 hours –But such cues are needed to keep them synchronized with day and night 33.10 Plants have internal clocks Figure 33.10

36. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plants mark the seasons by measuring photoperiod –the relative lengths of day and night The timing of flowering is one of the seasonal responses to photoperiod 33.11 Plants mark the seasons by measuring photoperiod

37. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Short-day plants flower when nights are longer than a certain critical length Long-day plants flower when nights are shorter than a certain critical length Figure 33.11 Darkness Flash of light Light Time (hr) Short-day (long-night) plantsLong-day (short-night) plants Critical night length

38. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A light-absorbing protein called phytochrome may help plants set their biological clock and monitor photoperiod Phytochromes were discovered during studies on how different wavelengths of light affect seed germination 33.12 Phytochrome is a light detector that may help set the biological clock

39. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings –Red light (660 nm) was found to be most effective at increasing germination –Far-red light (730 nm) both inhibits germination and reverses the effect of red light Figure 33.12A Time (hr) R FR R R R Critical night length Long-day (short-night) plant Short-day (long-night) plant R FR R

40. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings One form absorbs red light and the other absorbs far-red light –When red-absorbing P r absorbs red light, it is quickly converted to P fr –When P fr absorbs far-red light, it is converted back to P r Researchers have found that phytochrome reverts back and forth between two forms that differ only slightly in structure Figure 33.12B Red light Far-red light Slow conversion in darkness PrPr P fr

41. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plants also have a group of blue-light photoreceptors –These control light-sensitive plant responses, such as phototropism and the opening of stomata at daybreak

42. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Biologist and plant researcher Joanne Chory studies the popular model organism Arabidopsis Arabidopsis is a small, wild mustard whose complete genome was sequenced in 2000 Her research has had many agricultural applications 33.13 Talking About Science: Joanne Chory studies the effects of light and hormones in the model plant Arabidopsis Figure 33.13

43. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plants use both physical and chemical means to defend themselves against herbivores and pathogens Some plants produce an unusual amino acid called cananvanine –If an insect eats a plant containing cananvanine, the molecule is incorporated into the insect’s proteins in place of arginine, resulting in death 33.14 Defenses against herbivores and infectious microbes have evolved in plants PLANT DEFENSES

44. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Plants may recruit predatory wasps to kill caterpillars that feed on them Figure 33.14A 1 Damage to plant and chemical in caterpillar saliva PLANT CELL 2 Signal- transduction pathway 3 Synthesis of chemical attractants 4 Recruitment of wasp 5 Wasp lays eggs

45. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Avirulent plant pathogens interact with host plants in a specific way that stimulates both local and systemic defenses in the plant Local defenses include –microbe-killing chemicals –sealing off of the infected area

46. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hormones trigger generalized defense responses in other organs (systemic acquired resistance) –These provide protection against a diversity of pathogens for days

47. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 33.14B 1 Binding of pathogen’s signal molecule to plant’s receptor molecule Avirulent pathogen 2 Signal- transduction pathway 3 Enhanced local response 4 Hormones 5 Signal- transduction pathway 6 Additional defensive chemicals R-Avr recognition leading to a strong local response Systemic acquired resistance

48. Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Dr. Eloy Rodriguez is one of the world's leading experts on defensive chemicals produced by plants Zoopharmacognosy is the study of how animals medicate them- selves by eating plants that contain certain chemicals –It may lead to discoveries of medicinal chemicals that benefit humans 33.15 Talking About Science: Plant biochemist Eloy Rodriguez studies how animals use defensive chemicals made by plants Figure 33.15