CHAPTER 39 Plant Responses to Environmental Challenges

1. CHAPTER 39Plant Responses to Environmental Challenges

2. Chapter 39: Plant Responses to Environmental Challenges Plant–Pathogen Interactions Plants and Herbivores: Benefits and Losses Water Extremes: Dry Soils and Saturated Soils Too Much Salt: Saline Environments

3. Chapter 39: Plant Responses to Environmental Challenges Habitats Laden with Heavy Metals Hot and Cold Environments

4. Plant–Pathogen Interactions • Plants and pathogens evolve together. Review Figure 39.1 4

5. figure 39-01.jpg Figure 39.1 Figure 39.1

6. Plant–Pathogen Interactions • Plants can strengthen their cell walls when attacked. 6

7. Plant–Pathogen Interactions • Plant chemical defenses include PR proteins and phytoalexins. 7

8. Plant–Pathogen Interactions • In the hypersensitive response, cells produce phytoalexins and then die, trapping pathogens in dead tissue. 8

9. Plant–Pathogen Interactions • The hypersensitive response is often followed by systemic acquired resistance. • Salicylic acid activates further synthesis of PR proteins and triggers responses in other parts of the plant. 9

10. Plant–Pathogen Interactions • The hypersensitive response is nonspecific. • A more specific response, gene-for-gene resistance, matches up alleles in a plant’s resistance genes and a pathogen’s avirulence genes. Review Figure 39.3 10

11. figure 39-03.jpg Figure 39.3 Figure 39.3

12. Plants and Herbivores: Benefits and Losses • Grazing by herbivores increases the productivity of some plants. Review Figure 39.5 12

13. figure 39-05.jpg Figure 39.5 Figure 39.5

14. Plants and Herbivores: Benefits and Losses • Some plants produce secondary products as chemical defenses against herbivores. Review Table 39.1 14

15. table 39-01.jpg Table 39.1 Table 39.1

16. Plants and Herbivores: Benefits and Losses • Hormones, including systemin and jasmonates, participate in the pathways leading to defensive chemical production. Review Figure 39.6 16

17. figure 39-06.jpg Figure 39.6 Figure 39.6

18. Plants and Herbivores: Benefits and Losses • To avoid poisoning themselves, plants may confine toxic substances they produce to special compartments, or produce them only after cell damage, or may form enzymes and receptors that are not affected by the substances. 18

19. Water Extremes: Dry Soils and Saturated Soils • Desert annuals evade drought by living only long enough to take advantage of the brief period during which the soil has enough moisture to support them. 19

20. Water Extremes: Dry Soils and Saturated Soils • Some leaves have adaptations to dry environments: • a thickened cuticle, • epidermal hairs, • sunken stomata, • fleshy leaves, stems and spines • altered leaf display angles. 20

21. Water Extremes: Dry Soils and Saturated Soils • Other adaptations to dry environments include long taproots and root systems that die back seasonally. 21

22. Water Extremes: Dry Soils and Saturated Soils • The submerged roots of some plants form pneumatophores to allow oxygen uptake from the air. • Aerenchyma in submerged plant parts stores and permits the oxygen diffusion. 22

23. Too Much Salt: Saline Environment • A saline environment restricts water availability to plants. • Halophytes are adapted to such environments. 23

24. Too Much Salt: Saline Environments • Most halophytes accumulate salt, and some have salt glands that excrete the salt to the leaf surface. 24

25. Too Much Salt: Saline Environments • Halophytes and xerophytes have some adaptations in common. 25

26. Too Much Salt: Saline Environments • Aluminum, mercury, lead, and cadmium are among the heavy metals toxic to plants at high concentrations. 26

27. Habitats Laden with Heavy Metals • Rather than excluding heavy metals, tolerant plants deal with them after taking them up. • A given plant’s tolerance is limited to only one or two. 27

28. Hot and Cold Environments • High temperatures destabilize cell membranes and some proteins. 28

29. Hot and Cold Environments • Adaptations to elevated temperatures include the production of heat shock proteins. 29

30. Hot and Cold Environments • Low temperatures cause membranes to lose their fluidity. 30

31. Hot and Cold Environments • Ice crystals can puncture organelles and plasma membranes. 31

32. Hot and Cold Environments • Adaptations to low temperatures and freezing include a change in membrane fatty acid composition and production of antifreeze proteins. 32