Title: Control Systems in Plants Ch. 39 A grass seedling growing towards light
1Control Systems in PlantsCh. 39A grass
seedling growing towards light
2Control Systems
- Keep track of the time of day
- Notice seasons
- Sense gravity
- Sense direction of sunlight
3Plant Hormones
- Hormone
- compound produced by one part of an organism that
is transported and triggers a response in another
part
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6Plant Hormones
- Auxins
- main site of production is the apical meristem
- increases plasticity of cell wall
- promotes elongation of shoots
- promotes formation of adventitious roots fruit
growth - used as herbicides
- 2,4-D
- IAA
7Figure 39.8 Apical dominance with apical bud
(left), apical bud removed (right)
8Plant Hormones
- Cytokinins
- anti-aging
- stimulates cell division
- activates proteins for mitosis
- stimulates axillary bud growth
- Cytokinins and Auxins
- together control cell division and
differentiation
9Plant Hormones
- Gibberellins
- Primarily produced in roots and young leaves
- imbibition triggers its release
- promotes internode elongation (stem elongation)
- promotes seed germination (breaks dormancy)
- places a role in fruit growth
10Figure 39.11 The effect of gibberellin treatment
on seedless grapes
11Plant Hormones
- Abscisic acid
- produced in terminal bud
- prepares plant for winter
- closes stomata
- inhibits growth
12Plant Hormones
- Ethylene
- gas
- ripens fruit
- leaf abscission
- Stimulus is shortening days/longer nights and
cooler temps. (to a degree)
13Plant Hormones
- Oligosaccharins
- plant defense against pathogens
- cell growth and differentiation
- flower development
14Tropisms
- Growth responses that result in curvatures of the
whole plant toward/away from a stimulus - Phototropism
- stimulus is light
- Gravitropism
- stimulus is gravity
- Positive downward (roots)
- Negative upward (shoots)
15Tropisms
16Tropisms
- Thigmotropism
- stimulus is touch
17Turgor Movements
18Turgor Movements
- Reversible movements caused by changes in turgor
pressure - Rapid Leaf movements
- reduce water loss or protect from herbivores
- touch causes leaf to collapse (causes a rapid
loss of turgor pressure by cells causing them to
become flaccid) - motor cells lose K
- 10 minute restoration
- Mimosa clip
-
19Figure 39.27 Rapid turgor movements by the
sensitive plant (Mimosa pudica)
20Turgor Movements
- Sleep movements
- lowering of leaves to vertical position in
evening - raising leaves to a horizontal position in the
morning - one side of plant is turgid while the other is
flaccid - Daily changes in turgor pressure
21Figure 39.21 Sleep movements of a bean plant
22Control of Daily and Seasonal Responses
- Circadian rhythms
- does not require environmental cues
- light-dark cycle
- Entrained from environment internally set
23Figure 39.x1 Biological clocks
24Control of Daily and Seasonal Responses
- Photoperiodism
- Detect time of year by the photoperiod
- physiological response to night length
- Effects seasonal events such as flowering and
seed germination
25Photoperiodism
- Critical night length
- day length does not trigger flowering
- If daytime is interrupted, no effect on flowering
- If night period is interrupted by a short period
of light, plants do not flower - Could be effected by a single exposure or may
require several exposures
26Photoperiodism
- Short day plants
- night is longer than a critical length
- Flower in late summer, fall
- Long day plants
- night is shorter than a critical length
- Flower in late spring, summer
- Neutral day plants
- unaffected by photoperiod
- triggered by maturity
27Phytochromes
- Protein containing a chromophore responsible for
a plants response to the photoperiod - Alternate between 2 forms (Pr and Pfr)
- Pr only converts to Pfr in presence of light
- Pfr triggers many plant responses
- Pfr degrades back to Pr at night
28Figure 39.20 Phytochrome a molecular switching
mechanism
29Phytochromes
- Photoreceptors
- uses phytochrome to tell if light is present
- Red light most effective in interrupting night
length - Entrain the biological clock
- night length measured
- extremely accurate
30Figure 39.22 Photoperiodic control of flowering
31Figure 39.22 Photoperiodic control of flowering
32Figure 39.23 Reversible effects of red and
far-red light on photoperiodic response
33Figure 39.24 Experimental evidence for a
flowering hormone(s)
34Environmental Stress
- An environmental condition that can have an
adverse effect on a plants growth, reproduction,
survival - Water deficit, oxygen deprivation, salt stress,
heat, cold, herbivores
35Water Deficit
- Control systems in both leaves and roots
- Guard cells lose turgor and close
- Mesophyll releases abscisic acid
- Young leaf growth is inhibited
- Wilting reduces surface area
- Shallow root growth inhibited deeper roots
continue to grow
36Oxygen Deprivation
- Waterlogged soil lacks air spaces to hold oxygen
- May form air tubes from roots to the surface
- Submerged roots may be continuous with aerial
roots
37Salt
- Lowers water potential of soil causing a water
deficit even if enough water is present - Produce compatible solutes in response to
moderately saline soils - Keeps water potential of cells more negative than
the soil solution w/o admitting toxic quantities
of salt
38Heat
- Transpiration reduces temperature and keeps
enzymes from denaturing - Produce shock proteins
- a back up plan to transpiration
39Cold
- Subfreezing temps cause ice crystals to form in
protoplast - death
- Lipids become locked and causes a loss of
fluidity in membranes - Alter lipid composition by increasing saturated
fatty acids
40Herbivores
- Chemical
- Distasteful
- Toxic
- Recruit predatory animals
- Plants attract wasps that lay eggs in caterpillars
41Figure 39.29 A corn leaf recruits a parasitoid
wasp as a defensive response to an herbivore, an
army-worm caterpillar
42Defense Against Pathogens
- Gene-for-gene recognition
- Resistance to a disease depends on a precise
match up between an allele in a plant and an
allele in the pathogen
43Defense Against Pathogens
- Hypersensitive response
- chemical signaling system to resist infection
- phytoalexins
- Systemic acquired resistance
- protects unaffected tissues from a pathogen
spreading
44Figure 39.31 Defense responses against an
avirulent pathogen
45- A good candidate for one of the hormones
responsible for activating SAR is salicylic acid. - A modified form of this compound, acetylsalicylic
acid, is the active ingredient in aspirin. - Centuries before aspirin was sold as a pain
reliever, some cultures had learned that chewing
the bark of a willow tree (Salix) would lessen
the pain of a toothache or headache. - In plants, salicylic acid appears to also have
medicinal value, but only through the stimulation
of the systemic acquired resistance system.
46Extreme Plant AdaptationsA conclusion to the unit