Chapter 39: Plant Communication

1
Chapter 39 Plant Communication
2
Plants and their Environments

• Plants are living and respond to envir.
• They detect light and gravity especially.
• Plants respond by altering growth.
• Receptors receive signals and initiate a cellular
  response.
• Signal Transduction Pathway
• Ex Potatoe(?)s bud in dark not light
• b/c they grow in absence of light (underground)

3
Hormones? Chemical Signals

• Sent by one cell to initiate responses in others
• Can be introduced to soil or water to affect
  plant
• Minimal concentrations needed for big effect
• Triggers a cascade response
• Relative, not absolute levels of hormones
  regulate plant responses

4
Tropisms

• Whole body response of plant to stimuli.
• Phototropism Plant grows towards light.
• Coleoptile tip must be exposed to light. If
  removed or covered, no response.
• Detection at coleoptile, but growth occurs
  further down shoot.
• Chemical response sent from tip to shoot.
• Gravi-. Photo- and thigmo-tropism
• Gravity, light, touch

5
Phototropism

• Plants detect the intensity, direction, and
  wavelength of light.
• They will bend towards the area with the best
  light (intensity/quality)
• Phytochromes receptors

6
Phototropism is a Hormonal Response
7
Auxins Plant Growth Hormone

• Responsible for tropisms.
• 2 Theories
• Auxin concentrated on dark side of plant ?
  traditional theory
• An auxin inhibitor concentrated on light side of
  plant
• ? more recent research

8
(No Transcript)
9
(No Transcript)
10
Auxins

• Main function is to promote shoot elongation at
  low concentrations
• Loosen cell wall and allow increase H2O uptake
  (elongation)
• Also induce division in cambium
• Too high of a auxin will cause production of
  ethylene which inhibits elongation
• Causes rapid translation of proteins
• Gene regulation

11
Cytokinins

• Induce cytokinesis (cell division)
• Operate in balance with auxins
• Equal No differentiation, just division
• More cytokinin Shoot buds form
• More auxin roots form
• Auxins inhibit axillary growth, cytokinins
  promote it
• Slow aging

12
Gibberellins

• Produced in roots and leaves
• Stimutate growth of leaves and stems
• Elongation and division
• Works in cooperation with auxin to loosen cell
  walls (more H2O in elongation)

Effect of Gibberellins
13
Seed Dormancy and Gibberellins

• When conditions are appropriate, the release of
  gibberellins signals the seed to germinate
• May stimulate digestive enzymes to mobilize
  stored nutrients

14
Abscisic Acid (ABA)

• Slows growth
• Works antagonistically against the other growth
  hormones (gibberellins, auxins, cytokinins)
• Ratio b/t ABA and others
• Seed dormancy
• Allows plants to withstand droughts (close
  stomata)

15
Ethylene

• Leaf abscission (fall off)
• Fruit ripening
• Programmed cell death
• High auxins stimulate production
• Involved in thigmotropism (touch)
• Apoptosis

16
Apoptosis

• Systematic, preprogrammed (DNA) cell death.
• Enzymes break down organics (DNA, chlorophyll,
  RNA, proteins)
• Bursts of ethylene during autumn cause plants to
  lose their leaves and prepare for winter. First,
  they break down the organic molecules.
• Stored in stem parenchyma cells (reused by new
  spring leaves)

17
Seed Dispersal ? Fruits

• When a bear eats a piece of fruit, he eats the
  seeds.
• He doesnt digest the seeds.
• He poops the seeds.
• The poop is fertilizer for the seeds.
• Thanks Fozzy.

18
Ripening of Fruit

• Ethylene production causes ripening
• Storing fruits in a paper bag accelerates
  ripening (traps ethylene)
• Storing orange juice in the cabinet accelerates
  ripening

19
Circadian Rhythms

• Plants go through processes in a 24-hour
  (approx.) cycle
• When isolated, they lose sync with the external
  ques and regain when replaced
• Think Jetlag

20
Photoperiodism

• Plant leaves monitor the relative length of day
  and night
• Allows seasonal changes in plants (ie flowering)
• Short-day plants require light period shorter
  than a critical length to flower.
• Long-day plants flower when the light period is
  longer than a critical number of hours
• Day-neutral plants flower at maturity, regardless
  of day length

21
Short/Long Day Plants

• Short day long night
• Long Day short night
• Many plants require uninterrupted darkness hours
  to flower

22
Water Deficit

• Bright, sunny days ? plants can lose more H2O
  than they take in
• As H2O dec. the guard cells close stomata
• Inc. ABA production (close stomata)
• Inhibit growth of young leaves
• Leaves roll to dec. surface area
• All designed to decrease transpiration

23
Heat/Cold Stress

• Denatures plant enzymes
• Transpiration evaporative cooling
• Heat shock protein produced when temp. is
  raised beyond threshold
• Often bind to enzymes to prevent denaturization
• Extreme cold also freezes plants
• Many plants collect solutes (dec. fp)

24
Defense

• Some call other species to fight predators off
• Plants release signal chemicals to alert other
  plants of an infestation of herbivores