M5Ch16 Plant Responses Flashcards
Hormones found within plants
Hormones found within plants:
-Auxin
-Giberellin
-Ethene
-ABA (abscisic acid)
Roles of auxin in plants
Auxin:
-Controls cell elongation
-Prevent leaf fall (abscission)
-Maintain apical dominance
-Involved in tropisms
-Stimulate the release of ethene
-Fruit ripeningq
Roles of giberellin
Roles of giberellin:
-Causes stem elongation-Trigger the mobilisation of food stores in a seed at germination
-Stimulate pollen tube growth in fertilisation
Roles of ethene
Roles of ethene:
-Causes fruit ripening
-Promotes abscission in deciduous trees
Roles of ABA (abscisic acid)
Roles of ABA:
-Maintains dormancy of seeds and buds
-Stimulates cold protective responses for example antifreeze production
-Stimulates stomatal closing
Process of seed germination
Process of seed germination:
-Embryo activated and produced gyberellins
-Stimulates enzyme release that break down food stores in the seed
-ATP produced + digestive enzymes released
Where is the food store found for plants in order to geminate?
The food store is in the cotyledones in dicot seeds and the endosperm in monocot seeds
What is the experimental evidence supporting the role of giberellins in seed germination?
Experimental evidence of giberellin:
-Mutant varies of seeds bred that lacks gene which produce giberellin -> no germination
-Giberellin biosynthesis inhibitors applied to seeds and germination does not occur
Effects of auxin on plant growth
Effects of auxin on plant growth:
-Stimulate the growth of the main, apical shoot
-High auxin concentrations supress growth of lateral shoots, leading to apical dominance
-Low concentration of auxin promote root growth
How do auxins stimulate the growth of the main, apical shoot
How auxins stimulate growth of main apical shoot:
-Cell walls stretch more easily due to auxin
-Binds to receptor sites in membrane causing pH to fall - optimum for enzymes to maintain the wall plasticity
-Cells mature = auxin destroyed
-pH rises back and wall becomes rigid
How do high auxins supress the growth of lateral shoots? (apical dominance)
-Growth in the main shoort is stimulated by auxins but lateral shoot growth inhibited by it
-Lateral shoots grow stronger lower down stem where auxin less strong
Why does low concentrations of auxin promote root growth?
-Auxins used stimulate growth of main apical shoot by affecting cell wall plasticity so reduced amounts in roots increases root growth
What is synergism?
Synergism is when different hormones work together to produce a greater response
What is antagonism?
Antagonism is when opposing hormones have opposing effects and so do not work well together
What is Photoperiodism?
Photoperiodism is a plant’s sensitivity to lack of light in their environment
-Responsible for variety of changes in plants such as dormancy of leaf buds. time of flowering and tuber formation for overwintering
Abscission in deciduous plants
Abscission in deciduous plants:
-Lose their leaves in the winter as the cost of glucose required to maintain leaves and produce anti freezing chemicals is greater than glucose produced
How is freezing in plants reduced?
Freezing in plants are reduced by actively transporting salts into the vacuole and cyotplasm
-Freezing point lowered, water does not expand as freezing causes breakage of H bonds in cell wall
Stomatal control in plants
Stomatal control in plants:
Roots detect abiotic stress of lack of water -> hormone ABA produced and travels in vascular system -> ABA binds to receptor on stomata -> activates change in ionic conc of guard cells + reduces water potential and turgour -> closing cells and reducing water potential
Plant physical defences
Plant physical defences:
-Thorns, spiny leaves, inedible tissue, hairy leaves, stingers
Substances released from the plant as part of the chemical defence of plants
Chemical defences:
-Tannins
-Alkaloids
-Terpenoids
-Pheromones
Tannins
Tannins: bitter tasting to deter large animals, toxic to insects
Alkaloids
Alkaloids:
-Bitter tasting compounds
-Poisonsinsects
-Eg morphine, caffeine
Terpenoids
Terpenoids:
-Essential oils produced by plants
-Toxic to insects and gfungi
Pheromones
Pheromones:
-Chemical that affects the social behaviour of the same species
Behavioural plant defence
Behavioural plant defence:
-Folding in response to touch, which collapses to frighten large herbivores and dislodge small pests
-Occurs as a result of electrochemical change in cells
Plant responses to changes in their environment
Plant responses to changes in their environment:
-Phototropism = growth in response to light
-Geotropism = growth in response to gravitational pull
-Hydrotropism = growth in response to water
-Chemotropism = growth in response to chemicals
-Thigmotropism = growth in response to touch
Why is tropism important?
Tropism are important in plants, as if unable to response to their environments plants may become malnourished and dead
Why are monocotyledenous seedlings used in research on tropism?
Monocotyledonous seedlings are used most commonly in reseach on tropism as the stem has no lateral growth and change can be seen and manipulated rapidly
Phototropism in plants
-Phototropism = growth in response to light
-Result of auxins moving across root/shoot so stem bends towards direction in sunlight
-Shoots are more positively phototropic and roots are negatively phototropic
Outline the process of phototropism
Outline the process of phototropism:
-Shoot exposed to unilateral light source, cells are equal length
-Auxin moves to the shaded side of the plant, creating high conc
-Higher conc causes cells to elongate, making stem bind to light source
-Auxin transport stops and plant grows towards light source
How can we explore phototropism?
-Growing plants in omnilateral, unilateral or completely withou light then observing rates nad directions of growth
-Growing plants with different filters, to see which wavelength of light trigger phototropism
Geotropism in plants
Geotropism = plants sensitive to gravitational pull
-Shoots are negatively geotropic and roots are positively geotropic
What is a clinostate?
A clinostat is a contantly rotating horizontal drum which can cause a plant grown horizontally to grow straight out, as regular rotation causes equal force of gravity on all sides
Ethene and plants
Ethene is a gaseous plant hormone important in ripening climacteric fruit
Hormone rooting powders
-Auxin application to cut roots increase root growth
-Used on a large scale for micropropagation for clones
Use of synthetic auxins
Synthetic auxins:
-Fine balance of hormones lost = plants will die
-As metabolism is increased and rapid growth becomes unsustainable and plant dies
Commercial use of plant hormones
Commercial use of plant hormones:
-Auxins can be used in production of seedless fruit
-Ethene can be used to cause fruit to fall
-Cytokines prevent ripe fruit from ageing and control tissue development
-Giberellins delay ripening and ageing in fruit
