Plant Responses Flashcards
What are the differences between plant and animal hormones?
Animal:
Hormones secreted by glands
Carried in the blood stream across the body
Target specific cells by binding to receptors
Plant:
Produced in unspecialised cells anywhere in a plant
Diffuse from cell to cell so a local effect
Enter cells and can have many different effects
A single plant hormone can have multiple effects what is it called when 2 different hormones work together or oppose each other?
- synergistic effect
- antagonistic effect
What is a positive growth response?
Growing towards the stimulus
What different kind of tropism can you get?
Phototropism
Gravitropism
Hydrotropism
What does tropism mean?
A directional growth response
Describe phototropism,include the hormone and response mechanism
- a shoot tip is illuminated asymmetrically
- this stimulus causes auxin to move into the darker side
- auxin activates H+ pumps when bound to surface proteins
- this lowers the pH in the cell wall activated an enzyme that breaks bonds between microfibrils
- enabling the cell wall to stretch under turgor pressure
General idea of phototropism:
Light causes auxin to distribute unevenly
Cells away from the light elongate more so the shoot bends towards the light
What does the plant hormone gibberellin do?
- stimulates growth in stems between nodes, acts in synergy with auxin
- stimulate fruit development
- break seed dormancy by activating amylase which mobilises food store
What are some commercial uses of gibberellin?
- useful for sugar cane as a longer steam means more sugar
- weed killer, as stem grows too long the weeds fall and die
What do cytokinins do?
- oppose the action of auxin in apical dominance
- promote lateral bud growth
- promote cell division in meristems (cytokinesis)
Cell differentiation in plants depends on the conc of plant hormones in the area; if the conc of auxin is higher than cytokinin what do the cells become?
Auxin promotes the production of roots so root cells
What do the plant cells differentiate into if the conc of cytokinin is higher or equal to auxin conc
Cytokinin promotes the production of shoot cells
If cytokinin is greater then shoot cells
If conc is equal then a undifferentiated mass (callus)
What is apical dominance?
The control of growth via apical and lateral buds
What relationship do auxin and cytokinin have with lateral bud growth?
Antagonistic
Auxin inhibits lateral bud growth and cytokinin stimulates it
Explain why trees have a Christmas tree shape
The apical bud produces auxin, which passes down the phloem and inhibits the growth of lateral buds
Further down the stem the auxin concentration is lower so there is more growth in lateral buds
How does can adding a seed to a solution of gibberellin stimulate germination?
- gibberellin stimulates amylase production
- amylase will break down the starch into soluble maltose
- maltose can be transported to the embryo to provide energy for growth
Describe the structure of a barely seed:
- outer seed coat
- huge endosperm containing starch and gibberellin
- aleurone layer around the endosperm
- embryo
What is vital for germination?
The food store in the endosperm to be made available for the embryo
Describe germination and how it begins:
- the seed absorbs water
- this stimulates the embryo to secrete gibberellin
- gibberellin diffuses into aleurone layer
- gibberellin causes the aleurone layer to express the amylase gene producing the enzyme amylase
- amylase digests the starch in the endosperm into soluble maltose
- maltose is transported to the embryo for cellular respiration
Devise an experiment to test gibberellins importance for the breakdown of starch
- prepare the barley seeds by cutting them in half, some halves containing the embryo and some halves containing just the endosperm
- sterilise the seeds in a sterilising solution
- prepare agar plates to include starch in the medium, add a solution of gibberellin to half the plates
- place 4 cut halves of the seeds side down in each agar plate, 4 Gibb W/embryo,4 Gibb without embryo, 4 just embryo, 4 without embryo and Gibb
- seal the plates and incubate at 25 degrees c for 24 hours
- use iodine to flood each plate
- record colour of plate
What part of a seed produces the enzyme?
The aleurone layer surrounding the endosperm
What is photoperiodism?
A response to the length of the period of light and darkness
What is the light sensitive pigment in plants that causes flowering called?
Phytochrome
Where is phytochrome found ?
The shoots and leaves of plants
What 2 forms does phytochrome take and during night which form is it in?
Pfr (phytochrome far red)
Pr (phytochrome red)
During the day there is more red light so Pr is converted into Pfr
When do long day plants flower?
When the length of the dark period is shorter than a critical length to keep Pfr above the threshold
If it’s dark for long enough, the amount of Pfr that’s converted into Pr will exceed the threshold
When do short day plants flower?
When the length of darkness exceeds a critical length so that the concentration of Pfr falls below the threshold
What are day neutral plants?
Plants that aren’t affected by photoperiod as they grow in tropical conditions where day length doesn’t vary
What is photomorphogenesis?
The control of growth and development in plants by specific wavelengths of light (using phytochrome)
Give 2 examples of photomorphogenesis:
- Pfr stimulates germination in some seeds
- some plants grow tall and don’t make chlorophyll until light is detected by Pfr (etiolation)
What is florigen?
A plant hormone not yet discovered that works synergistically with gibberellin to promote flowering
