TOPIC 12- Plant Control Systems and Behaviour

hormones

____ are produced in regions of active growth like at meristems, embryos, leaves, and fruit

auxin

____ are produced in SAM and young leaves

auxin

functions of ____ include:

o  Promotes cell elongation

o  Promoting axillary bud dormancy

o  Promoting lateral root development

cytokinins

____ is produced in the roots, embryo, and fruits

cytokinin

functions of ____ include:

o  Promotes cell division

o  Promotes axillary bud growth

abscisic acid

______ produced by all plant cells

abscisic acid

functions of ___ include:

• Promotes seed dormancy

  • Seeds become dormant to help them stay alive during winter

• Inhibits growth

• Closes stomata

gibberellins

____ produced in meristems, leaf primordia and embryos

gibberellins

functions of ____ include:

o  Promoting fruit growth

o  Stimulate cell division and elongation

o  Promote seed germination

ethylene

gaseous hormone that can be produced by any part of a plant

• synthesis may be stimulated by wounding and stress

ethylene

functions of ____ include:

• response to stress / obstacles

• fruit ripening

• leaf abscission

phototropism

behaviour fueled by auxin; behaviour in which plant grows towards light

1. shoot tip produces auxin

2. auxin is spread down the length of the cell; moves towards the shady side of the plant

3. this promotes growth towards the light source

gravitropism

behaviour fueled by auxins; behaviour in which the plant roots grow with or against gravity

• horizontal roots:

  • caused by the statolith in the root cap

    • statolith- starch-filled plastid that helps organisms sense gravity

  • statolith settles in the lower side of the root, distorting its cytoskeleton

  • stauxin is moved to the lower side of the root, and it inhibits cell elongation upside down; so the roots grow downwards

acid-growth hypothesis

explains cell elongation in auxins

1. auxins pump protons through modified proton pumps to acidify the cell wall

2. low pH activated expansins

3. wall enzymes chop up polysaccharide that holds the fibrils

4. at the same time, the new bonds are forming and new microfibrils are being created

5. the cell wall becomes loose, which lessens wall pressure, which allows the elongation (growth)

longer

to make roots grow ___: low cytokinin concentration, and high auxin concentration

longer

to keep shoot apical meristem growing ___: low auxin concentration and high cytokinin concentration

• this is why herbs like basil grow more leaves when we cut stems off

• by removing the SAM, we are reducing the plant’s concentration of auxin

• this increases shoot / leaf growth

cell wall

gibberellins works well with auxins and works to loosen the ___ ___, this is helpful for:

• stem elongation and fruit growth

embryo

gibberellins are produced in the ____ of a newly rinsed seed

• triggers the release of alpha-amylase, which digests the starch stores in the yolk of the embryo, and turns it into glucose

• this triggers germination

dormancy

high abscisic acid concentration induces seed ___

• this is only reversed once the ABA is washed off by rain or melting snow

opens

during periods of drought, ABA accumulates in the leaves:

• this ___ potassium channels on the leaves leading to the stomata closing

• unfortunately this also slows the rate of photosynthesis since the stomata is closed

ethylene’s affect on stress response

·Ethylene produced at the shoot tip accumulates causing:

• Slowing elongation, thickening of stem, and bending of the stem

·Once the obstacle is avoided, the concentration of ethylene decreases and normal growth resumes

• The larger the obstacle, the more the concentration of ethylene

ethylene in fruits

·      Cellulose loosening; cell wall breaks down, so the fruit is softened

·      Starch breakdown into sugars makes fruit sweet

·      Attractive scents, and attractive colors to attract pollinators and animals to eat the seeds of the plant

triple step stress response with ethylene

• slowing of elongation

• thickening of stem

• bending of stem

decreases ethylene

as auxin concentration ___ in leaves, they are more vulnerable to ___ which causes leaf abscision

cellular signalling

o  Reception of the signal by special proteins

o  Transduction- small molecules that amplify the signal gotten from reception

o  Response to the signal

phytochromes

photoreceptors that detect light and trigger the change towards de-detiolation behaviour