Chapter 39: Plant Responses to Environmental Challenges
CHAPTER 39
Plant Responses to
Environmental Challenges
Chapter 39: Plant Responses to Environmental Challenges
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
Chapter 39: Plant Responses to Environmental Challenges
Chapter 39: Plant Responses
to Environmental Challenges
Habitats Laden with Heavy Metals
Hot and Cold Environments
Chapter 39: Plant Responses to Environmental Challenges
Plant–Pathogen Interactions
• Plants and pathogens evolve together.
Review Figure 39.1
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Chapter 39: Plant Responses to Environmental Challenges
Figure 39.1
Figure 39.1
figure 39-01.jpg
Chapter 39: Plant Responses to Environmental Challenges
Plant–Pathogen Interactions
• Plants can strengthen their cell walls when
attacked.
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Chapter 39: Plant Responses to Environmental Challenges
Plant–Pathogen Interactions
• Plant chemical defenses include PR proteins
and phytoalexins.
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Chapter 39: Plant Responses to Environmental Challenges
Plant–Pathogen Interactions
• In the hypersensitive response, cells
produce phytoalexins and then die, trapping
pathogens in dead tissue.
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Chapter 39: Plant Responses to Environmental Challenges
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.
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Chapter 39: Plant Responses to Environmental Challenges
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
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Chapter 39: Plant Responses to Environmental Challenges
Figure
39.3
Figure 39.3
figure 39-03.jpg
Chapter 39: Plant Responses to Environmental Challenges
Plants and Herbivores:
Benefits and Losses
• Grazing by herbivores increases the
productivity of some plants.
Review Figure 39.5
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Chapter 39: Plant Responses to Environmental Challenges
Figure
39.5
Figure 39.5
figure 39-05.jpg
Chapter 39: Plant Responses to Environmental Challenges
Plants and Herbivores:
Benefits and Losses
• Some plants produce secondary products as
chemical defenses against herbivores.
Review Table 39.1
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Chapter 39: Plant Responses to Environmental Challenges
Table
39.1
Table 39.1
table 39-01.jpg
Chapter 39: Plant Responses to Environmental Challenges
Plants and Herbivores:
Benefits and Losses
• Hormones, including systemin and
jasmonates, participate in the pathways
leading to defensive chemical production.
Review Figure 39.6
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Chapter 39: Plant Responses to Environmental Challenges
Figure
39.6
Figure 39.6
figure 39-06.jpg
Chapter 39: Plant Responses to Environmental Challenges
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.
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Chapter 39: Plant Responses to Environmental Challenges
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.
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Chapter 39: Plant Responses to Environmental Challenges
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.

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Chapter 39: Plant Responses to Environmental Challenges
Water Extremes: Dry Soils
and Saturated Soils
• Other adaptations to dry environments
include long taproots and root systems that
die back seasonally.
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Chapter 39: Plant Responses to Environmental Challenges
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.
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Chapter 39: Plant Responses to Environmental Challenges
Too Much Salt: Saline
Environment
• A saline environment restricts water
availability to plants.
• Halophytes are adapted to such
environments.
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Chapter 39: Plant Responses to Environmental Challenges
Too Much Salt: Saline
Environments
• Most halophytes accumulate salt, and some
have salt glands that excrete the salt to the
leaf surface.
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Chapter 39: Plant Responses to Environmental Challenges
Too Much Salt: Saline
Environments
• Halophytes and xerophytes have some
adaptations in common.
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Chapter 39: Plant Responses to Environmental Challenges
Too Much Salt: Saline
Environments
• Aluminum, mercury, lead, and cadmium are
among the heavy metals toxic to plants
at high concentrations.
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Chapter 39: Plant Responses to Environmental Challenges
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.
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Chapter 39: Plant Responses to Environmental Challenges
Hot and Cold Environments
• High temperatures destabilize cell
membranes and some proteins.
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Chapter 39: Plant Responses to Environmental Challenges
Hot and Cold Environments
• Adaptations to elevated temperatures
include the production of heat shock
proteins.
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Chapter 39: Plant Responses to Environmental Challenges
Hot and Cold Environments
• Low temperatures cause membranes to lose
their fluidity.
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Chapter 39: Plant Responses to Environmental Challenges
Hot and Cold Environments
• Ice crystals can puncture organelles and
plasma membranes.
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Chapter 39: Plant Responses to Environmental Challenges
Hot and Cold Environments
• Adaptations to low temperatures and
freezing include a change in membrane fatty
acid composition and production of
antifreeze proteins.
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