Plant Responses

1. Abiotic factors

   Nota:

   • such as drought, high temperatures, low temperatures e.g. carrots produce their own anti freezing mechanisms proteins bind to ice crystals and lower the temperature that water freezes so stopping the ice crystals from growing
2. Biotic Factors

   Nota:

   • predation, white clover produces substances which are toxic to cattle, 
3. Increase chances of survival
   1. move to light

      Nota:

      • move to light so they can photosynthesise 
   2. sense gravity

      Nota:

      • so they can grow roots which anchor them in the soil and so there roots and shoots grow in the correct direction
   3. sense of touch

      Nota:

      • significant to climbing plants so they can reach sunlight

Nota:

• is a plant growth response to an external stimulus, where the direction of  growth is always related to the stimulus  

1. Slow

   Nota:

   • respond by regulating their growth which can take a while 
2. Directional response
   1. Negative

      Nota:

      • away from the stimulus e.g. shoots away from gravity
   2. Postitive

      Nota:

      • towards the stimulus e.g. shoots towards sunlight
3. different types
   1. photostropism

      Nota:

      • towards light
   2. Chemotropism

      Nota:

      • towards chemical
   3. hydrotropism

      Nota:

      • towards water
   4. thermotropism

      Nota:

      • towards temperature
4. Oppostie to Nastic

   Nota:

   • a quick non directional change due to external stimulus 
   1. Changes due to water

      Nota:

      • rather than plant growth regulators, ation potential causes change in turgidity of hinge cells causing them to swell and cause movment  when a petal closes leaves at night instead of causing growth involves tempoary changes in tempoary changes in cell volume
   2. quick

1. made by..

   Nota:

   • groups of cells in different parts of the plant, not organs like animal
2. Carried in..

   Nota:

   • the phloem and the xylem
3. bind too..

   Nota:

   • recceptos like animal hormones do
4. Hard to examine because..

   Nota:

   • only found in tiny quantities nd usually two or more hormones act together having very different effects when either of them are present and often they have different effects in different species and in different parts of the same plant 
5. Phototropism experiments
   1. Darwin

      Nota:

      • intact coleoptile moves towards light, no tip = no movement, tip that is shaded does also not bend towards light
      1. cut tip
      2. non cut tip
      3. cap
      4. Conclusion

         Nota:

         • a growth stimulus is produced in the top of the coleoptile the growth stimulus is transmitted to the area of cell elongation the cells on the shaded side of the coleoptile elongate more then those on the light side 
   2. Boysen Jensen

      Nota:

      • a sheet of mica (insol) inserted through the shaded half of the coleoptile and it stops the curvuture response, its inserted in the illimuniated side and does not stop the curvuture response. the tip is cut off and tip is replaced with block of geletian and tip placed ontop of gelatine = normal curvuture response 
      1. insoluble martieral
         1. Placed in the side
      2. soluble matieral
         1. placed inbetween cleoptile tip and shoot
      3. Conculsion

         Nota:

         • matierals which are not permeable to water such as mica can stop the curvurture response but matierals which are soluble to water such as gelatine do not interfere with the curvuture response
   3. Went

      Nota:

      • placed celoptiles on agar for some time and blcoks from agar were cut out, blocks where placed on the celoptile which had had its tip removd, it would be placed to one side, the celoptile side which had the agar placed on it would grow faster then other side causing it to bend. the more celoptile tips placed on the agar the more it would bend
      1. Celoptile tips on agar
      2. agar cubes on to the shoot missing the tip
      3. the dark
      4. Conclusion

         Nota:

         • curvuture response is due to chemical which moves from the tip and effects cell elongation
6. 1.Blue light
   1. 2. Hits phototropins

      Nota:

      • proteins that sit in the plasma membrances of cells 
      1. 3. Phosophorylates phototropin

         Nota:

         • if blue light comes from one side it phosophorylates that side, if it comes from another it phosphorylates the other side
         1. 4. triggers transporter protein

            Nota:

            • in plasma membrance of some of the cells (in the sides of the cells)  in the shoot which actively moves auxin out of the cell either the phosphorylation causes transporter proteins to work harder on either side or for more to move to one side (the shady side) 
            1. 5. Auxins build up

               Nota:

               • on the shady area of the plant casuing the plant cells to elongate on the shady side causing it to bend to the light
               1. 6.auxin bind to receptor in shoot
                  1. 7. effects the transport of ions though the pm
                     1. 8. build up of h ions in cell wall = low ph
                        1. 9. Activates enzymes

                           Nota:

                           • activated by the low ph
                           1. 10. cell takes up water via osmosis

                              Nota:

                              • making them longer
                              1. 11. swell and become longer

                                 Nota:

                                 • this is a permenant change 

Nota:

• the presense of apical meristem inhibits lateral mersitem division and therefore lateral growth = apical dominance 

1. apical meristem

   Nota:

   • near the tip of the shoot, contains small undifferentiated cells that are constantly dividing and growing increasing the length of the stem.
   1. Terminal bud

      Nota:

      • where apical meristem is 
2. Lateral buds

   Nota:

   • buds on either side of them also contain meristems that divide but do not become active whilst the apical meristem is in tact and differentiating 
3. Test it

   Nota:

   • remove the terminal bud and the lateral buds will grow. 
   1. Cut tip off two shoots

      Nota:

      • tip produces auxins so if cut off no auxins are made
      1. apply IAA to one of them

         Nota:

         • symthetic auxin 
         1. the one with IAA will have apical dominance
         2. no IAA will show no apical dominance
   2. tip a growing shoot upside down
      1. lateral buds grow and no apical dominance
         1. this is because auxin is not transported upwards towards gravity

            Nota:

            • so auxin does not reach the lateral buds and does not inhibit them
   3. how to test it
      1. plant 30 plants

         Nota:

         • same age, heigh and weight in pots 
         1. count the number of side shoots

            Nota:

            • growing from each stem
            1. remove the tips of 20
               1. apply auxin past IAA to 10
               2. apply past with nothing in
                  1. let all 3 groups grow for the same number of days & in the same conditions

                     Nota:

                     • light intensity, temperature, water = controlling variables which makes the experiment reliable then count again how many side shoots there are 
                     1. Tabulate data
            2. leave 10 as they are = control

               Nota:

               • always need control for comparison
4. Auxin

   Nota:

   • constantly made in the terminal bud (tip of the shoot) and is transported downwards from cell to cell and accumilates in the nodes the lateral branches = inhibits their activity 
   1. Made in terminal bud
      1. transported down cell by cell

         Nota:

         • move via diffusion, active transport or in the phloem
         1. accumilates in lateral bud nodes

            Nota:

            • there is uneven disribution of auxins in the plant causes growth at different areas
            1. inhibits their growth
5. exam q

   Nota:

   • explain why side shoots grow when the terminal buds are removed? auxins are produced in the terminal buds, auxins inhibit lateral grwoth, remove terminal bud lowers auxin conc so lateral buds can grow
6. exam q

   Nota:

   • auxin could effect the change in growth of stems; cause cell longation, increase plasticity of cell walls by buid of h ions, enzyme synthesis, vaccuolation

Nota:

• gibberelin causes rapid stem elongation only need small quanitites to grow huge

1. effect gene expression
   1. dwarf beans variates lack gene for GA
   2. short pea plants lack dom allele for GA
   3. can make rice lack gene that codes for enzymes involved in GA production
   4. why is this useful?

      Nota:

      • more energy is put into yeild then into stem, stem is usually not useful product
   5. 1. GA move through PM into cell
      1. 2, binds receptor protein
         1. 3. RP binds to another RP

            Nota:

            • the previouse receptor protein binds to another receptor protein 
            1. 4. resulting in the breakdown of the dela protein

               Nota:

               • dela protein normally bound to transcription factor preventing it from transcribing
               1. 5. transcription factor released
                  1. 6. transcription can occur
2. Gib & Auxin

   Nota:

   • can be synergistic = work together for large effect e.g. very tall plant or antagonostic = opoose each others actions e.g. gibberlin causes side shoots where as auxin trys to inhibit
3. experiments
   1. can water plants with dilute GA
4. exam q

   Nota:

   • how dwarf variety arisen? mutatuion, change in allel freq, random genetic enggerneering, altered mrna, selective breeding

Nota:

• 3 hormones involved = ethene, ABA and auxin

1. leaf abscission

   Nota:

   • trees in temperate countrys drop their leaves in winter, it is triggered by shortening day lengths 
   1. why?

      Nota:

      • can't photosynthesis much in winter due to low light levels and temperature so there is no real use for leaves & they can drain resources
      1. reduce water loss

         Nota:

         • through the leaf surfaces
      2. avoid frost damage
      3. avoid fungal infections
2. 1. auxin decrease

   Nota:

   • auxin inhibits abscission, if making lots of auxin will not fall off tree this makes the leaf more sensitive to ethene. Auxin and ethene work antagonistically 
   1. 2. Ethene increase

      Nota:

      • this inhibits auxin production furthur, ethene is a gas that moves through air spaces between cells via diffusion, it tends to be produces by ageing and maturing frutis or plants, as the leaf gets older it produces more ethene 
      1. 3.abscission layers grows in the petiole

         Nota:

         • made of thin walled cells which are weakened by enzymes that hydrolyse the polysaccarhides in their cell walls
         1. pertiole

            Nota:

            • base of the leaf stalk
         2. 4. trees grows a protective tissue

            Nota:

            • where the leaf will break off creating a scar which will prevent pathogens and microorganisms from entering the plant this is made of cells that have suberin in their cell walls
            1. suberin

               Nota:

               • waxy waterproof substance
            2. 5. the leaf falls off at the abcsission layer

               Nota:

               • ethene causes cells in the abcission layer to exapand causing the cell walls to break leaving the suberin layer of cells behind
3. ABA

   Nota:

   • abscisic acid = stress hormone released by plants, was thought played a large part in leaf abscission but does not 

1. Auxin
   1. prevent abscission

      Nota:

      • fruits stay on the plant longer so the can be harvested when they are ripe
   2. Formation of fruits

      Nota:

      • even when the plant has not be pollinated = seedless fruits 
   3. Root Formation

      Nota:

      • can be applied to the lower cut end of a shoot to encourage root formation, widely used in vegetative propogation - roots grown from cuttng, planted the lots of cuttings taken from orginial and auxin added = lots of the orginial plant
      1. veg prop
   4. selective herbicides

      Nota:

      • synthetic auxins such as IAA can be used as selective herbicides, they kill only certain weeds but not others (kill dandelions and daisys but not grass and ceral crops) 
      • they also make the weed grow long stems and no leaves so the  weed grows to fast but can't take up any nutrients or water due to lack of leaf
      1. how

         Nota:

         • in through the auxin transporter but not out again, natural auxins go out cell through facialiated diffusion = build up in cell unti eventually die
   5. exam q

      Nota:

      • commercial uses of auxin; stimulate root hair growth, induce seedless fruit, avoid need for pollination, increase fruit set, increase fruit size, prevent abscission, 
2. Ethene
   1. promotes ripening

      Nota:

      • can be harvested before they are fully ripe and then sprayed with ethene in store to make them ripe this means they can travel long distances without becoming damaged and old
3. Gibberellin
   1. promote growth

      Nota:

      • increase the movment of sucrose which in turn brings in more water via osmosis so they are larger and sweeter
      1. sucorse
         1. osmosis
   2. prevent abscission

      Nota:

      • allows grower to leave fruit to maximum before picking crops - citrus fruits
      1. citrus fruits
   3. increase sucrose in sugar cain

      Nota:

      • in cold temperatures the stems do not grow as long, increasing sucrose makes them grow longer
   4. germination

      Nota:

      • stimulates germination in seeds = beer making GA spayed onto barley grain to make them germinate and the germinating seeds produce enzymes that break down starch to maltose and yeast + maltose = alchol
   5. seedless

      Nota:

      • similar to auxin = cuases production of fruits without pollination = seedless fruits 
      1. grapes