plant responses Flashcards
How do plants coordinate functions?
Plants produce hormones in one region and then transport from cell to cell through transport tissues to have an effect on another part of the plant.
What are the main plant hormones?
Auxins, gibberellins, abscisc acid (ABA), ethene
Why are scientists unsure about the details of plant responses?
Plant hormones work at very low concentrations so they are hard to isolate and measure
There are multiple interactions between different chemical systems so it is hard to isolate a singular chemical system
What is required for seed germination before plant growth?
The seed will absorb water , the embryo will activate and produce gibberellins.
Gibberellins will stimulate the production of enzymes which break down food stores in the seed.
Embryo plant uses these food stores for ATP to build materials required to break out the seed.
What does evidence suggest for gibberellin function?
That gibberellins switch on genes which code for digestive enzymes such as amylase and proteases.
What are some experimental evidence that support the claim that gibberellins are involved in seed germination?
1) Mutant variables of seeds with the lack of gene that produces gibberellins do not germinate. When gibberellin is added externally, they germinate
2) Gibberellin biosynthesis inhibitors are added , they do not germinate. When inhibition is removed and gibberellins are applied, seed can germinate.
What are auxins and where are they produced?
Auxins are produced in the shoots and roots and the meristem tissue and are involved as growth stimulants in plants.
They stimulate the growth of the main apical shoot.
How do auxins stimulate growth?
Auxins affect plasticity of the cell walls.
Auxin molecules bind to the specific receptor on the cell membrane and cause the ph to fall to 5,
This is the optimum temperature for enzymes to keep the wall flexible and plastic. The cell wall will expand as they absorb water and change shape.
As cells mature, auxin is destroyed and the ph levels return to normal, the cell wall will become rigid and in a fixed shape.
What is apical dominance?
Apical dominance is the result of high concentrations of auxin as they suppress the growth of lateral shoots,
Growth in the main shoot is stimulated quickly by auxin, lateral shoots are inhibited and will move down the stem.
Further down the auxin concentration is lower hence lateral shoots grow more strongly.
What is some experimental evidence for the role of auxins in apical dominance?
If the apical shoot is removed, the auxin producing shoot is removed and therefore lateral shoots are freed from dominance and will grow.
However when auxin is supplied artificially to the cut apical shoot, apical dominance is reasserted and lateral shoot growth is restricted,
What promotes and inhibits root growth?
Low concentrations of auxin promote root growth.
High concentrations of auxins inhibit root growth,
Up to a given concentration, the more auxin that reaches the roots, the more they grow.
If the apical shoot is removed, the amount of auxin reaching the roots is greatly reduced and root growth will slow and stop.
Restoring auxin artificially will return the growth.
How do gibberellins affect plant growth?
What is the evolutionary advantage of less gibberellin?
Gibberellins affect the length of the internodes of plants.
Plants that have little gibberellins have short stems , for example dwarf plants which have had their gibberellin synthesis path interrupted.
Evolutionary advantage: Reduces waste and less vunrable to weather damage.
What are abiotic stress? Give some examples.
The negative impact of non-living factors on living organisms (plants) for example the weather and lack of water.
What is photoperiodism? What are some responses to photoperiodism?
The idea that plants are sensitive to a lack of light in the environment
Responses: Breaking of dormancy in leaf buds and timing of flowering.
Where do plants sensitivity to light come from?
Results from light sensitive pigments called phytochrome which exists in two forms being Pr and Pfr that absorb different levels of light, the ratio is dependent on the levels of light.
What do the lengthening if dark periods trigger in plants?
Triggers a number of changes in plants such as abscission or leaf fall and a period of dormancy during winter months.
How is auxin and ethene hormones involved in the abscission of leaves?
Falling light levels lead to a fall in auxin concentration.
Fall in auxin concentration leads to the production of ethene.
The abscission zone is made up of two layers of cells sensitive to ethene.
Ethene initiates gene switching in these cells to produce new enzymes (cellulase)
Cellulase will digest and weaken the cell walls in the outer layer of the abscission zone known as the seperation layer.
How is a protective layer formed after the seperation layer?
Vascular bundles are sealed off.
Fatty material is deposited into the cells on the stem side of the seperation layer which forms a protective layer when the leaf falls.
