B16 Flashcards
Auxins
Cell elongation, prevent leaf abscission, tropisms, stim. ethene release, fruit ripening.
Gibberellins
Stem elongation, mobilise food stores (germintation), stim. pollen tube growth (fertilisation).
Ethene
Fruit ripening, promote abscission.
Abscisic Acid (ABA)
Stim. stomata closing, maintain seed dormancy.
Germination
- Absorb water.
- Embryo activates.
- Prod. giberellins.
- Stim. prod. of enzymes.
- Break down food stores.
- Embryo use stores for ATP prod.
- Grow & break seed coat.
Synergism
Different hormones working together (complementary), give an increased response. Achieves fine control over plant response.
Antagonism
Hormones with opposite effects. E.g. growth & inhibition.
The balance between determines response.
Commercial Uses: Control Ripening
Ethene ripen climacteric fruit (cont. ripen after harvest e.g. banana). Harvest when fully formed but not ripe, transport with less damage, expose to ethene gas, inc. selling time.
Commercial Uses: Rooting Powders & Micropropagation
Auxin on cut shoots –> grows roots (propagates new plant). Agriculture & horticulture propagate large scale with micropropagation (hormones control thousands of new cell prod. and differentiation).
Commercial Uses: Hormonal Weedkillers
Weeds compete with crops & interrupt metabolism. Synthetic dicot auxins absorbed by weeds, inc. growth rate, unsustainable, weeds die. (Crops - narrow leaved monocots, weeds - broad leaved dicots).
Commercial Uses: Other Hormone Uses
Auxins (prod. seedless fruit).
Ethene (promote fruit dropping e.g. cotton).
Cytokinins (prevent ageing of ripened, control tissue development in micropropagation).
Giberellins (delay ripe/ageing, improve size/shape).
Abiotic Stresses
High wind, excess H2O, temp. change, day length.
Herbivore Stresses
Physical Defences - wax, above ground covered with cutin, subrin (walls), bark, thorns, hairy leaves.
Chemical Defences - if physical penetrated. Kill, ill , repel.
Abiotic: Leaf loss
Cold winter = less pts.
More efficient to lose leaves.
Abiotic: Daylight sensitivity
‘Photoperiodism’ = sensitivity to lack of daylight. Longer daylight hrs –> leaves bud/flowers bloom.
Abiotic: Leaf abscission
Less light, ethene switches on genes which stimulate enzymes. Enzymes digest & weaken cell walls at abscission zone. Leaf separates, leaves waterproof scar to protect plant.
Abiotic: Preventing freezing
Some plants with chemicals act as a natural antifreeze. Activated in winter, reversed by inc. temp.
Abiotic: Stomatal control
ABA dec. water potential/tugidity of guard cells (close), less H2O lost. Open again to cool plant.
Chemical defense: Tannins
Bitter, inactivate digestive enzymes in saliva of animals.
Chemical defense: Alkaloids
Bitter, nitrogenous, poisonous. Toxic to insects (caffeine), release to soil to stop germination around it (protect other plants).
Chemical defense: Terpenoids
Toxins & oils. Pyrethrin (insecticides) and Citronella (put insects off).
Chemical defense: Pheromones
Warn others in species. Tree attacked –> release pheromones –> absorbed by leaves on other branches –> leaves make callose, helps protect if attacked.
Auxin conc. in shoots
Apical Dominance.
High conc. = suppresses the growth of shoots.
Low conc. = lateral shoots inc. growth.
Tropisms
Growth response to environmental cues/unidirectional stimulus.
+ve = towards stim. -ve = away from stim.
Phototropism
Controlled by IAA (auxin).
Inc conc. = elongation in shoots and inhibit in roots.
Unilateral light = growth on dark side, IAA diffuse to shaded side, shoot bends towards light (+ve phototropism). Roots bend away from light (-ve phototropism).
Geotropism
Controlled by IAA (auxin).
Gravity. Shoots -ve geotropism (grow upwards), roots +ve geotropism (towards stim).
Ensure shoots receive light and roots in soil.
