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the green planet 2 > mechanisms of plant growth and plant defence > Flashcards

mechanisms of plant growth and plant defence Flashcards

1
Q

middle lamella

A

layer of adhesive between two cell walls (between two cells)

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2
Q

characteristics of meristem cell walls

A
  1. thin
  2. plastic (can be stretched and remain at the stretched length)
  3. allow growth.
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3
Q

bark (cork) cell wall characteristics

A
  1. waterproof - stops tree losing water and absorbing water and getting soggy.
  2. germ proof - keeps out micro-organisms.
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4
Q

xylem cell wall characteristics.

A
  1. waterproof
  2. non-compressible (has to carry weight of the tree)
  3. rigid
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5
Q

root cap cell wall characteristics

A
  1. slimy (lubricates passage through soil)
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6
Q

two ways in which we can found out the components of a cell wall

A
  1. microscopy - stain cell wall components =makes them visible
  2. isolate cell walls in a test tube and analyse the test tube chemically.
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7
Q

advantages and disadvantages of cell wall microscopy

A

ADVANTAGE - provides brilliant spatial resolution (can see where the substance is)

DISADVANTAGE - doesn’t tell you exactly what the substance is.

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8
Q

advantages and disadvantages of chemical cell wall analysis

A

ADVANTAGE - can get every detail of chemical substance bing studied - very precise.

DISADVANTAGE - can’t see where the substance is - it is somewhere in that test tube.

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9
Q

how are cell walls isolated?

A
  1. smash up tissue in a blender to free walls of other components
  2. filter cell walls out
  3. dissolve starch
  4. filter out starch
  5. dissolve proteins
  6. filter out proteins
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10
Q

polysaccharide

A

polymeric molecule composed of sugars

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11
Q

what composition is usually found in cell walls

A
  • 90% polysaccharides
  • 10% structural glycoprotein
  • 30% lignin/cutin/suberin
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12
Q

three classes of polysaccharides

A
  1. pectin
  2. hemicellulose
  3. cellulose
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13
Q

how to separate the three polysaccharide classes from a cell wall.

A
  1. treat cell walls with a chelating agent - brings PECTINS into solution.
  2. dissolve insoluble with sodium hydroxide which brings HEMICELLULOSE into solution
  3. the third left over insoluble is CELLULOSE
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14
Q

physical properties of the three polysaccharide classes.

A

PECTIN - can gel

HEMICELLULOSE - viscous

CELLULOSE - water insoluble, tough, not stretchable.

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15
Q

biological roles of the three polysaccharide classes.

A

PECTIN - intercellular glue. lubrication of cell wall for expansion.

CELLULOSE - scaffolding of cell walls in the form of microfibrils.

HEMICELLULOSE - tether microfibrils together.

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16
Q

monosaccharides that make up PECTIN

A

galacturonic acid

galactose

arabinose

rhamnose

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17
Q

monosaccharides that make up HEMICELLULOSE

A

glucose

xylose

arabinose

mannose

galactose

fucose

glucuronic acid

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18
Q

monosaccharides that make up CELLULOSE

A

glucose

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19
Q

turgor pressure

how does it work

A

pressure inside each cell which drives cell expansion.

  1. higher concentration of solutes inside the cell drives osmosis of water from outside to inside the cell.
  2. this uptake of water creates pressure.
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20
Q

why does turgor pressure require energy?

A

creation of solutes inside cell uses ATP.

solutes are either…
- taken up.
- synthesised by the cell.

21
Q

how does turgor pressure not cause the cell to burst?

A

cell wall exerts a back pressure against turgor pressure - reaches equilibrium of pressure from both directions.

22
Q

definition of growth

A

irreversible increase in volume.

23
Q

how can turgor be zeroed?

A
  1. wilting
  2. freezing-thawing
  3. bathing in concentrated sugar.
24
Q

elastic cell extension

A

expansion from turgid for to zeroed form.

25
Q

plastic cell expansion

A

expansion from turgid state to zeroed state.

26
Q

how do microfibrils impact direction of cell expansion

A
  1. microfibrils lie parallel with each other. they can be separated but not stretched and thus get longer instead of fatter.
  2. microfibril lie unorganised in cell wall - shape will become more balloon-like.
27
Q

how is growth rate increased.

A

growth rate is proportional to the amount by which the turgor pressure exceeds the yield threshold.

yield threshold - before this point no growth occurs.

28
Q

what can rate of cell expansion be controlled by?

A
  1. onset of germination
  2. hormonal treatments
  3. light/dark
  4. maturation
  5. genetic dwarf//tall
29
Q

m in plant growth

A

modulus of extensibility

30
Q

how can a cell alter its modulus of extensibility?

A
  1. loosen of existing cell wall material
  2. tightening of existing cell wall material
  3. synthesis of new wall polysaccharides.
31
Q

how does cell wall loosening happen?

A
  1. microfibrils pulled apart by turgor pressure.
  2. xyloglucan tethering them together becomes taut.
  3. this tether is cut to further loosen the cell wall.
32
Q

structure of xyloglucan

A
  1. backbone made up of glucose residues
  2. xylose is attached to 3 of 4 glucose residues.
  3. galactose is attached to some of the xylose.
  4. fucose is attached to some of the galactose.
33
Q

what can cut xyloglucan in cell wall loosening?

A
  1. endo-beta-glucanase (cellulase)
  2. xyloglucan endotransglucosylase (XET)
  3. hydroxyl radicals (*OH)
34
Q

how does cellulase split xyloglucan?

A

hydrolyses glucose-glucose bond to break it which splits the xyloglucan.

35
Q

how does XET split xyloglucan?

A

a hybrid xyloglucan chain is created by combining a piece from two others.
- XET catalyses this reaction.

36
Q

how do hydroxyl radicals split xyloglucan?

A

hydroxyl radicals created in the Fenton reaction are very reactive.

they react with the xyloglucan which splits the chain.

37
Q

expansins

A

proteins responsible for cell wall creep (another method of cell extensibility).

expansions break hydrogen bonds keeping xyloglucan tethered to microfibrils.

38
Q

how can cell walls be re-tightened?

A
  • phenolic substances attached to polysaccharides can oxidatively couple together.
  • this pulls polysaccharides together.
  • peroxidase catalyses this reaction.
39
Q

how is cell wall synthesised?

A

microfibrils are built at the plasma membrane.
- glucose from UDP-G gets added to glucose chain in a Rosette in membrane.

matrix polysaccharides are synthesised in the Golgi bodies.

40
Q

in which biologically important situations might a cell wall be attacked?

A
  1. holes appear in walls
  2. separation layer of abscission zone (leaves fall of trees naturally)
  3. ripening fruit —> tissue softening
  4. wall loosening for cell expansion
  5. penetration by pathogenic fungus - through cuticle and epidermal cell wall.
  6. penetration of interior cells.
  7. rotting
  8. digestion in animals guts.
41
Q

what industrially important situation requires attacking cell walls and why is it so expensive?

A

exploitation of straw for biofuels.

waste cell walls are indigestible so lots of energy needed to break them down.

42
Q

what two enzyme types digest polysaccharides?

A

glycanases (endo-hydrolases)

glycosidases (exo-hydrolases)

43
Q

how do glycanases digest polysaccharides?

A

attack the middle of the polysaccharide.

the enzyme splits a glucose-glucose bond by hydrolysis. this creates two smaller polysaccharides.

44
Q

how do glycosidases digest polysaccharides?

A

attack polysaccharides from the non-reducing end releasing one sugar at a time.

45
Q

enzyme proofing agents

A

help defend cell walls

46
Q

how do we know that lignin is an enzyme proofing agent?

A
  1. if we de-lignify wood it decays faster (take lignin out and it doesn’t have defence)
  2. if we add lignin to paper it resists digestion by cellulase.
47
Q

synthesis of lignin

A
  1. phenylalanine (precursor of lignin) is turned into coniferyl alcohol.
  2. this makes a free radical.
  3. two free radical forms join together to form an AB dimer.
  4. lots of dimers together make lignin.
48
Q

structure of lignin

A

its a heptamer.

made up of coniferyl alcohol building blocks.

49
Q

characteristics of lignin

A
  1. waterproof
  2. indigestable
  3. very abundant

the green planet 2 (10 decks)

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