Plant Responses Flashcards
Tannins - HERBIVORY
Bitter tasting and bind to proteins in gut to make it difficult to digest
Alkaloids - HERBIVORY
Biter tasting, noxious smell or poisonous e.g tobacco producing nicotine
Releasing pheromones- HERBIVORY
Alarm pheromones can trigger nearby plants to produce tannins in response to grazing
Corn plants release pheromones when being eaten by caterpillars that attract wasps that lay eggs in the caterpillar
Mimos pudica response to touch by folding up which can knock off insects or scare off animals
Abiotic stress
Non living environmental factor that can harm a plant. E.g mineral deficiency, drought, pollution. ( changes to environment )
Plants respond to abiotic stress by producing antifreeze enzymes which lowers the temperature at which water freezes so stops ice crystals from forming
May contain tannins
May contain bitter tasting nitrogenous alkaloids
Release cell signalling pheromones to trigger defensive responses
Tropism
Response to directions stimulus
Positive growth towards stimulus
Negative growth away from stimulus
Phototropism - plants respond to light
Geotropism - growth in response to gravity
Hydrotropism - growth in response to water
Thermotropism - growth in response to temperature
Thigmotropism - growth in response to contact with an object
Growth hormone AUXIN
Speed or slow down plant growth
- produced at top of shoot
- stimulates growth in apical shoots by cell elongation ( cell wall stretches )
Involved in tropic responses e.g IAA - inhibits growth of lateral buds which means apical dominance
Apical dominance
Therefore less competition between buds on same plant + conserving energy
If you remove apical bud, side shoots start growing
Lateral buds grow at bottom where there is low auxin concentration
Growth hormone GIBERELLINS
Giberellins produces in young leaves and seeds
- Don’t inhibit growth
- Trigger germination - cause breakdown of starch into glucose in seeds so it can be used for growth
- Can be inhibited by IAA
- fruit growth and flowering
IAA
An auxin
Shoots show positive phototropism as IAA diffuses to shaded side of tip so there’s uneven growth
IAA moves to the side, cells elongate and shoot bends towards light
Why roots show positive phototropism
Gravity causes IAA to accumulate on lower side of root.
IAA inhibits elongation of root cells
Cells on upper side of root elongate faster so root tip bend’s downwards
Synergistic and antagonistic
Synergistic - work together for plant growth
Antagonistic - oppose each others actions e.g auxin inhibits lateral growth but gibberellins stimulate lateral growth
Leaf loss ( abscission )
As leaf ages cytokinin and auxin levels lower but ethene levels increase
Triggers production of cellulase enzymes which weakens leaves by breaking down cell walls in abscission layer
Ethene stimulates leaf loss and inhibits growth :
causes formation of abscission layer at bottom of leaf stalk
stimulates cells to expand,
cells walls to break,
leaves fall off
Stomata closure - ABA
Closed stomata means less water is lost by transpiration
Guard cells full of water - plump and turgid and stomata is open
When flaccid - stomata is closed
ABA triggers stomata closure
ABA binds to receptors on guard cell membranes
Causes Ca2+ ion channels to open and diffuse
Positive feedback causes other ion channels to open
Increase in Ca2+ conc causes ion channels such as K+ to diffuse out of out of guard cell.
Raises water potential and water leaves the cell by osmosis
Guard cells become flaccid so stomata closes
Experimental evidence that auxins maintain apical dominance
Auxin production in apex means high levels of ABA and inhibit growth of side shoots
When apex removed auxin level drops so ABA levels drop
Cytokinins diffuse evenly to promote bud growth in other parts of plants = lateral growth
Experimental evidence showing gibberellins control stem elongation
Stem elongation :
Tall plants have higher gibberellin conc than dwarf plants
Germination :
Mutant seeds with non functional giberellin gene do not germinate unless gibberellin applied externally
Inhibitors of gibberellin production, prevent germination
Commercial uses
Farmers
Auxin - weed killer and herbicide as weeds grow fast and cannot get enough water to sustain themselves
Rooting hormone to stimulate cuttings to produce roots
Fruit industry
Ethene - stimulates enzymes to break down cell walls and chlorophyll and convert starch to sugars so speeds up fruit ripening. E.g bananas and ethene
Promotes lateral growth and fruit drop
Gibberellins - brewing beer for malt production
Increase sugar cane yield, prevent lodging
