Plant Hormones Flashcards
(59 cards)
Define ‘plant hormones’
Chemicals that are produced in one region of the plant and transported both through transport tissues and from one cell to another
What are the 6 roles of auxins?
Control cell elongation Abscission Maintain apical dominance Involved in tropisms Stimulate release of ethene Involved in fruit ripening
What are the 3 roles of gibberellins?
Causes stem elongation
Trigger the mobilisation of food stores in a seed at germination
Stimulate pollen tube growth in fertilisation
What are the 2 roles of ethene?
Causes fruit ripening
Promotes abscission in deciduous trees
What are the 3 roles of ABA?
Maintains dormancy of seeds and buds
Stimulates cold protective responses
Stimulates stomatal closing
Why are scientists still unsure about the details of many plant responses?
Plant hormones work at low concentrations so isolating them and measuring changes is difficult
Multiple interactions between chemical systems so difficult to isolate one chemical system
Explain the process of how germination is triggered
Seed absorbs water and the embryo is activated
Gibberellins start to be produced
Stimulates production of enzymes that breakdown the food stores of the seed
Embryo plant uses the food stores to produce ATP for building materials so they can grow and break out seed coat
Gibberellins switch on genes which code for amylases and proteases which are key for germination
Give 2 pieces of evidence that support the role of gibberellins in the germination of seeds
Mutant varieties of genes have been produced without gibberellins and they do not germinate. When fertilised with gibberellins externally they germinate.
Gibberellin biosynthesis inhibitors are applied to seeds, they don’t germinate as they cannot break dormancy
Give an example of an auxin
IAA- indoleacetic acid
Where are auxins produced?
Tips of roots and shoots and in the meristems
How does lateral growth in a plant occur?
Apical bud removes
Decrease in the concentration of auxins leads to the growth of lateral shoots
How does apical dominance occur?
High concentrations of auxins inhibit the growth of lateral shoots and apical shoots is stimulated
Explain the mechanism of action of auxin
Auxin binds to receptors on the cell membrane
H+ ions are actively pumped across the membrane into the cell wall
Build up of H+ ions lowers the pH to 5
Decrease in pH activates proteins called expansins
Cellulose cell wall becomes more plastic and there is cell expansion
What are the benefits of having low levels of gibberellins?
The plants are less vulnerable to damage by weather and harvesting
Define synergism
Different hormones working together, complimenting each other and giving a greater response than they would have individually
Define antagonism
Substances have opposite effects, the balance between them determining the response
Give 5 abiotic stresses
Seasonal changes in day length Temperature changes Lack of water Too much water High wind
Why is not efficient for plants to continue photosynthesizing through winter?
As plants need to produce enough glucose to support respiration in leaves
Glucose required for chlorophyll based process that protect the plant against freezing
How do deciduous trees combat seasonal changes and the inefficiency of photosynthesis?
Lose all of their leaves in the winter and remain dormant until the days lengthen and temperatures rise
Explain the phenomenon that is ‘wind rock’
Trees in full leaf are top heavy
During winter months there are often heavy winds
Heavy winds can cause uproot which damages the roots.
Stems may break which damages the xylem and phloem tissue in the stem.
How do trees respond to ‘wind rock’?
Losing all their leaves in winter months to make them less vulnerable as less heavy
Explain how ethene triggers abscission
Ethene is produced when the days get shorter
Ethene triggers the genes to switch on
Enzymes produced
Enzymes digest and weaken the cell walls of the cells in the separation zone
Vascular bundles supplying the leaf are sealed off and the cells bellow the abscission zone swell
Leaves are pushed off
How does the plant respond to leaf loss via abscission?
Fatty material deposited in the cells on the stem side of the separation layer
What is the abscission zone?
Two layers of cells that are sensitive to ethene
