Plant Responses to the Environment
description
Transcript of Plant Responses to the Environment
![Page 1: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/1.jpg)
Plant Responses to the Environment
Chapter 45
![Page 2: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/2.jpg)
Plant Hormones
• Hormones – chemicals secreted by cells, transported to other cells where they exert effect
• Released in response to an environmental stimuli
• Promote growth, development, aging
![Page 3: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/3.jpg)
Six Plant Hormones
• Auxins• Gibberellins• Cytokinins• Ethylene• Abscisic acid• Florigens
![Page 4: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/4.jpg)
Auxins
• Promote or inhibit elongation in target cells– Shoot – high conc. causes elongation– Root – low levels stimulate elongation, high conc.
inhibit
• Synthetic auxin (2,4 D) is used to kill dicots• Commercially used to promote root
formation in plant cuttings, stimulate fruit development, delay fruit fall
![Page 5: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/5.jpg)
Gibberellins
• Primarily in plant shoots• Promote stem elongation by increasing
cell elongation and division• Stimulate bud sprouting, flowering, fruit
production and development, seed germination
• Produced in the shoot apical meristem, young leaves, plant embryos
![Page 6: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/6.jpg)
Cytokinins
• Promote cell division• Synthesized in root apical meristem• Inhibit formation of root branches,
cause nutrients to be transported to leaves, stimulating chlorophyll production and delaying aging
• Commercially - sprayed on cut flowers to keep them fresh
![Page 7: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/7.jpg)
Ethylene
• Gas• Produced in plant tissues, released in
response to a range of environmental stimuli• Stress hormone – produced in response to
wounding, flooding, drought, extreme temp.• Stimulates weak celled abscission layers -
leaves, petals, fruit drop off at appropriate times
• Commercially – used to ripen fruit
![Page 8: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/8.jpg)
Abscisic Acid
• Synthesized in tissues throughout the plant
• Helps plants to withstand unfavorable environmental conditions
• Causes stomata to close when water is scarce
• Promotes root growth, inhibits stem growth in dry conditions.
• Helps maintain dormancy
![Page 9: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/9.jpg)
Florigens
• Synthesized in leaves
• Control flowering in response to environment
• Discovered in 2007
![Page 10: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/10.jpg)
Hormones regulate plant life cycles
• Hormones are produced in response to an environmental stimulus
• These hormones may influence the activity of genes (activate, repress)
![Page 11: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/11.jpg)
Maintaining Dormancy of Seeds
• In temperate zones, seeds remain dormant until spring• Cold weather reduces abscisic acid,
preparing plant for spring germination
• In desert plants, some seeds have high levels of abscisic acid in their coats. It may be washed away by rain
• Grasslands, chaparral, forest – require fire for germination
![Page 12: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/12.jpg)
Gibberellin Stimulates Germination
• -Abscisic acid and +Gibberellin = germination
• Gibberellin is produced by the embryo• Enzymes break down starch for energy
![Page 13: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/13.jpg)
Auxin controls Orientation
• Light and gravity help the seedling figure which way is up
• Auxin controls phototrophism – growth towards light, in shoots
• Gravitropism – growth to/away from gravity, in shoots and roots
• Gravirtopism and phototrophism work together to cause shoot to grow upward
![Page 14: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/14.jpg)
Auxin mediates Gravitropism
• Vertical stem – auxin distributed evenly
• Horizontal stem – position detected and auxin distributed to lower side of stem. • Lower cells elongate, bending stem upwards
(-gravitropism)• When stem is vertical auxin is evenly
distributed
![Page 15: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/15.jpg)
Auxin from the shoot tip travels down and collects in the root tip
Auxin, produced in the shoot tip, is distributed evenly across the shoot and root as it travels downward
root
seed
shoot
(a) The shoot and root are orientedvertically
Gravitropism
![Page 16: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/16.jpg)
Auxin is transported to the lower side of theshoot, where it stimulates cell elongationand causes the stem to bend upward
Auxin is transported to the lower side of theroot, where it inhibits cell elongation andcauses the root to bend downward
(b) The shoot and root are orientedhorizontally
Gravitropism
![Page 17: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/17.jpg)
Negative Gravitropism
Positive Gravitropism
![Page 18: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/18.jpg)
Auxin mediates Phototropism
• Auxin accumulates in the side of the shoot that is away from the light.• Cells elongate and
bend towards the light
![Page 19: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/19.jpg)
Animation: Hormone Characteristics
![Page 20: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/20.jpg)
Animation: Hormone Transport and Activity
![Page 21: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/21.jpg)
Auxin mediates Root Elongation
• Toward gravity• If root is horizontal, they sense gravity
and cause auxin transport to lower side• Lower side cells elongate, causing root
to grow towards gravity
• How do they sense gravity? Statoliths – starch filled plastids settle into the lower part of the cell
![Page 22: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/22.jpg)
Statoliths May Be Gravity Detectors
root
statoliths
nucleus
cell inroot cap
![Page 23: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/23.jpg)
Plant responds to Environment
• When shoot or root push against soil, ethylene is given off.
• Elongation slows and cells become thicker and stronger
• More able to force their way through soil
• Dicots – ethylene causes formation of hook in forming shoot
![Page 24: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/24.jpg)
Thimotropism
• Directional movement or growth in response to touch
• Cell elongation on contact side is inhibited, tendrils grow
• Etheylene may be produced by cells touching the object
![Page 25: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/25.jpg)
Shoot and Root Branching
• Controlled by Auxin and Cytokinin
• Growth of shoot must be balanced by root growth• Water, mineral, anchorage of plant
• Stems – auxin inhibits later bud growth to form branches, cytokinin promotes this growth
• Root – cytokinin stimulates root branching, auxin promotes this growth
![Page 26: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/26.jpg)
Apical Dominance
• Pinching back the tip of a plant causes bushy growth because apical meristems release auxin which suppresses bud development into branches.
![Page 27: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/27.jpg)
Lateral bud sprouting
• Auxin is transported from the stem to the root, decreasing in concentration.
• Cytokinin is transported from the root to the stem, decreasing in concentration.
• Lateral buds closes to shoot receive enough auxin to inhibit growth, very little cytokinin = remain dormant
• Lower lateral buds receive less auxin and more cytokinin = stimulate to grow into branches
![Page 28: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/28.jpg)
Root branch formation
• Auxin, transported down from the stem stimulates branch roots to form
• Cytokinin produced in the root apical meristem inhibits root branching and is transported from the root towards the shoot
• Roots closer to the shoot develop branch roots
• Gradient of hormones keeps size of root and shoot in balance
![Page 29: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/29.jpg)
Lateral buds are inhibited by high auxin levels
Branch roots develop (optimal ratio of cytokinin to auxin)
Branch roots are inhibited by high cytokinin levels
Lateral buds develop into branches (optimal ratio of auxin to cytokinin)
auxin
cytokinin
high
high
shoot tip
root tip
Gradient of Auxin and Cytokinin
![Page 30: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/30.jpg)
Response to Light and Dark
• Timing of flowering and seed production is crucial
• Environmental clues like water and temperature are unpredictable
• Day length is very reliable• Shortening vs. lengthening days
![Page 31: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/31.jpg)
It’s about the amount of darkness
• Day-neutral plants – flower independently of day length • Roses, tomatoes, cucumbers, corn
• Long-day plants – flower when uninterrupted dark is shorter than species-specific duration• Iris, lettuce, spinach, hollyhocks
• Short-day plants – flower when uninterrupted dark is longer than species-specific duration• Cockleburs, chrysanthemums, asters, potato, goldenrod
• It is really more about the amount of darkness than light
![Page 32: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/32.jpg)
long night short night
night day
interrupted night
lon
g-d
ay p
lan
t(i
ris)
sho
rt-d
ay p
lan
t(c
hry
san
them
um
)d
ay-n
eutr
al p
lan
t(r
os
e)
The Effects of Darkness on Flowering
![Page 33: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/33.jpg)
Phytochrome
• Plants measure darkness using a biological clock that isn’t well understood
• Each time the phytochrome molecule is exposed to light, the clock resets to 0
• If a plant needs 8 hours of dark to flower but is interrupted with a flash of light at 4 hours, the clock will reset
• Light changes the shape of the phytochrome molecule
![Page 34: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/34.jpg)
conversion in light
absorbsred light
Pr
(inactive)Pfr
(active)Pfr stimulates or inhibits a
response
conversion in dark
absorbsfar-red light
both forms are present in daylight
The Light-Sensitive Phytochrome Pigment
![Page 35: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/35.jpg)
Author Animation: Phytochrome
![Page 36: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/36.jpg)
Author Animation: Morning Glory
![Page 37: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/37.jpg)
Animation: Seedling Elongation
![Page 38: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/38.jpg)
Florigen Stimulates Flowering
• Leaves produce florigen in response to the biological clock
• Transported on phloem to the apical meristem where it activates genes that are responsible for flowering
![Page 39: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/39.jpg)
Coordination of Seeds and Fruit
• Auxin and gibberellin promote growth of ovary
• Apply to fruit and they grow larger and looser
![Page 40: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/40.jpg)
Ethylene
• Unripe fruit is green, bitter• Ripened fruit turns color &
attracts animals
• Ethylene gas stimulates ripening, as they ripen fruits give off ethylene gas to stimulate ripening of adjacent fruit
• Bananas & tomatoes are picked & shipped green
![Page 41: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/41.jpg)
Senscence
• Genetically programmed series of events that prepare the plant for winter
• Ethylene production increases
• Auxin and cytokinin production decreases
• Starches and chlorophyll are broken down and stored in the stem and roots
![Page 42: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/42.jpg)
The Abscission Layer
• A layer located where the fruit or leaf join the stem
• Ethylene promotes breakdown of this layer
• Leaves/fruit drop at correct time
• Can also be triggered by stress
![Page 43: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/43.jpg)
Plant Communication
• Plants summon insect bodyguards• When attacked by caterpillars, corn releases
chemicals, stimulated by volicitin (in caterpillar saliva)
• Parasitic wasps are attracted to chemical, lay eggs in caterpillar
• Lima beans, attacked by spider mites release chemical that attracts carnivorous mite that preys on spider mite
![Page 44: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/44.jpg)
A caterpillar chews on a corn leaf, leaving traces of saliva that contains volicitin
1
Volicitin and leaf damage cause the plant to synthesize and release volatile chemicals
2
The wasps lay their eggs on the caterpillar, which will provide food for their larvae
4
The released chemicals attract female parasitic wasps
3
A Chemical Cry for Help
![Page 45: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/45.jpg)
Animation: Chemical Messengers
![Page 46: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/46.jpg)
Plant Defense
• Some plants, when damaged by insects, produce a signaling molecule that moves through the plant.
• The plant then makes a distasteful chemical
• Radishes and caterpillars
![Page 47: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/47.jpg)
Warning the Neighbors
• Healthy plants sense chemicals released by neighbors that have been wounded by insects.
• Salicylic acid methyl salicylate (volitile)
• Neighbors boost their defenses
![Page 48: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/48.jpg)
Mimosa
• Thigmotropism - sensitive to touch
• Stimulated by electric signals conducted through motor cells at the base of each leaf
![Page 49: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/49.jpg)
Carnivorous Plants
• Sundew - movement of trapped insects triggers thigmotropism in the hairs, secrete sticky goop, smothering the insect
• Bladderwort – trapdoor is sprung by insect, opens inward suddenly, sucking insect into the bladder where it is digested.
![Page 50: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/50.jpg)
A Sundew and Its Insect Prey
![Page 51: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/51.jpg)
The Bladderwort Snares Tiny Aquatic Organisms
![Page 52: Plant Responses to the Environment](https://reader036.fdocuments.us/reader036/viewer/2022062422/56813d1f550346895da6dfdc/html5/thumbnails/52.jpg)
Author Animation: Venus Fly Trap