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Plant responses & hormones (p&a r - 5.1.5 a, b, c, d, e, f) -…

- - - - Tannins - toxic to microbes & large herbivores. In leaves they’re find in upper epidermis. Make the leaf taste bad. In roots they prevent infection from microbes
      - Alkaloids - derived from amino acids, in plants they’re a feeding deterrent to animals, tasting bitter. Located in growing tips & flowers & outer layers of stems & roots
      - Pheromones - chemicals which are released by 1 individual & can affect behaviour or physiology of another
  - - - Shoots grow towards the light
      - Positive phototropism
    - - Roots grow towards pull of gravity
        
        Positively geotropic
        
        Better anchorage & nutriences
      - Shoots grow away from pull of gravity
        
        Negatively geotropic
    - - Pollen tubes growing down the style, attracted by chemicals from the ovary
        
        Positive chemotropism
    - - shoots of climbing plants e.g. ivy – grow towards & around structures for support
      - Don’t waste energy on supporting structures
        
        Positive thigmotropism
- - - - Prevent fruit & leaf drop in low concentrations
      - High concentration promote fruit drop
      - Useful to farmers cause they can harvest fruit in 1 go
    - - using auxins in vert low concentrations to promote root growth
    - - Applying auxin to flowers promotes ovule growth - but there has been no fertilisation - resulting in seedless fruit
    - - Stimulates shoot growth so much that the plant can't support own weight & buckles under own weight & dies
  - - - Delays ageing (senescence) in citrus fruit - can leave them unpicked for longer
      - Changes apples shape (longer)
      - Increases stalk length in grapes - gives more space to grow therefore they are bigger
    - - Once the barley seeds absorb water, enzymes can work
      - Aleurone layer produces amylase to break down starch store
      - Production of amylase is switched on gibberellins
      - Brewers adding extra gibberellins will speed up this process
      - There will then be more sugar for fermentation
    - - cause stems in sugar cane to elongate
        
        more sugar per stem (extra 4.5tons per hectare
    - - Takes a long time for conifers to mature and be able to reproduce
      - Gibberellins promote seed formation at a younger age
      - Breeding experiments / artificial selection is speeded up
    - - Adding gibberellin inhibitors to plants can reduce stem length
        
        Helps produce short stocky houseplants
      - Prevents ‘lodging’ in some plants with tall stems
        
        In winter the heads of these plants collect water and the weight causes the stems to snap. Difficult to harvest!
        
        Gibberellin inhibitors produce shorter stems to prevent lodging
  - - - Bananas have to travel long distances on boats without ripening too quickly
      - Ethene is produced by ageing tissues and promotes ripening
      - To inhibit ethene production we transport the bananas in the following conditions..
        
        Low temperature, Low oxygen, High carbon dioxide
      - Bananas stay unripe for longer and survive the long journey
      - Silver salts inhibit ethene also and are used to increase the shelf-life of cut flowers
- - - - Auxin promotes active transport of H^+ ions by a protein pump, into the cell wall, decreasing its pH.
      - The decreased pH activates wall loosening enzymes called expansins
        
        break bonds in the cellulose
      - wall becomes less rigid & cell expands
  - - - Bakanae is a fungal disease which makes rice plants grow excessively tall and spindly (not healthy)
      - the fungus releases a compound called GA3 (Gibberellic acid)
      - GA3 is a member of the gibberellin family of compounds
      - Adding GA3 to dwarf plants makes them taller
    - - Plants with the alleles “le le” are homozygous recessive and will be Dwarf
        If a rice plant has just one dominant “Le” allele it will be tall (Normal)
    - - https://docs.google.com/document/d/1IsbjeCe9Cekfumqqp-lXsQIZD655amM5DYJcuAOuvDM/edit
      - GA1 needs to be made in the plant or it will not be tall
      - If “Le” is not present then the Enzyme which converts GA20 to GA1 is missing
      - This enzyme must be present or a rice plant cannot produce GA1
      - Without this type of Gibberellin, the plant will be a dwarf.
      - A plant must have an Le allele to be Tall
      - In le le (homozygous recessive) plants this enzyme is missing so GA20 cannot be converted to GA1
      - these plants will be dwarf
    - - There is another type of dwarf rice plant called the MUTANT dwarf.
        This variety does not have the enzyme which converts ent-kaurene to GA12 -aldehyde
      - https://docs.google.com/document/d/1Skd2E96c1p4IYu64qaNUwwkojFirpjbI-qNWxfOKNI4/edit
      - If GA12 -aldehyde cannot be made then nothing else following this can be made either including the all important GA1
      - In the mutant dwarf, everything in red cannot be made because of the missing enzyme.
      - There is a blockage in the pathway
      - If GA1 is not made then the plant will be a dwarf
    - - https://docs.google.com/document/d/1hHV3WYCmhcWUNTv8xkQuAhtfgl2-JKqj3NcRhbH719c/edit
      - They took a MUTANT Dwarf plant and grafted it onto an le le Dwarf plant
        
        cause mutant to grow tall
      - The le le Dwarf has huge amounts of GA20 building up but cannot do anything with it
        The Mutant Dwarf which has the enzyme for converting GA20 into GA1 now for the first time gets a supply of GA20 and can make GA1 for itself and so grow tall
- - - - some scientists support auxins as being responsible only.  Others dispute this
    - - If an Auxin Transport Inhibitor is applied to the Apex of a healthy plant, lateral buds would grow because they are not receiving auxin. 
    - - Gocal found that in some plants auxin concentration in the lateral buds actually increases when the apex of the plant is removed.
    - - Abscisic acid is generally inhibitory
      - High auxin levels in the apex keep abscisic acid levels high in some plant regions
      - Removing the apex lowers auxin concentration and therefore also abscisic acid
      - Lack of abscisic allows lateral buds to grow
    - - Cytokinins promote lateral bud growth
      - Applying cytokinins to lateral buds will overide apical dominance and the buds will grow
      - High concentration of auxin cause most of the cytokinins to move towards the shoot apex from other areas of the plant
      - Removing the shoot tip, cytokinins spread more evenly around the plant, promoting growth in the lateral buds
- - - - https://docs.google.com/document/d/1nWHnx7uqDOHoRZhFScjy2k6ELBp39JpiSsD7mLb5lHk/edit