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plant cell wall - exam Flashcards

1
Q

Importance of the Cell Wall in Plant Development

chatgpt

A

The plant cell wall is essential for plant development as it determines cell shape, guides differentiation, and allows the plant to withstand internal pressure and external forces. It also plays key roles in growth, intercellular communication, and defence.

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2
Q

Cell Wall Formation and Structure
Primary Cell Wall:

chatgpt

A

Thin, flexible wall rich in pectin and cellulose, allowing growth.

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3
Q

Cell Wall Formation and Structure
Secondary Cell Wall:

chatgpt

A

Thickened, often lignified wall for strength and function (e.g. xylem).

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4
Q

Cell Wall Formation and Structure
Built from:

chatgpt

A

– Cellulose microfibrils (scaffolding)
– Hemicellulose (cross-linker)
– Pectin (gel matrix, flexibility)
– Proteins (regulation and customization)

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5
Q

Cell Wall Function in Immunity

chatgpt

A

The cell wall acts as both a physical and biochemical barrier against pathogens.
It provides:

Passive defence (e.g., lignification, trichomes)

Active defence (e.g., ROS, callose, PRR signalling) Pathogens fight back by modifying pH, degrading polysaccharides, and manipulating Ca²⁺, creating an ongoing evolutionary arms race.

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6
Q

Cell Wall Function in Growth

chatgpt

A

The plant cell wall allows for controlled expansion. Growth occurs when turgor pressure stretches the wall, and proteins like expansins regulate where and how much the wall loosens. The orientation of cellulose fibres controls the direction of growth.

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7
Q

Concept of Turgor and Its Implications

chatgpt

A

Turgor is the pressure exerted by the fluid inside the cell (mainly from the vacuole) against the cell wall. It is essential for:

Cell expansion and growth

Maintaining tissue structure (preventing wilting)

Driving nutrient transport and mechanical strength Loss of turgor leads to wilting, growth arrest, and reduced metabolic activity.

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8
Q

PLANT CELL WALL STRUCTURE:
global challenges:
zero hunger

A

: creating a world free of hunger by 2030 (food security)
o Ukraine war -> massive disruption to food supply chain

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9
Q

PLANT CELL WALL STRUCTURE:
global challenges:
climate action

A

: taking urgent action to combat climate change and its devastating impacts
o Extreme weather events
 Driver of this is CO2

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10
Q

PLANT CELL WALL STRUCTURE:
global challenges:
life lands

A

: protect, restore and promote sustainability use of terrestrial ecosystems, sustainably manage forests, combat desertification and halt and reserve land degradation and halt biodiversity loss

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11
Q

PLANT CELL WALL STRUCTURE:
global challenges:
affordable and clean energy

A

about ensuring access to clean and affordable energy

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12
Q

PLANT CELL WALL STRUCTURE:
global challenges:
good health and well being

A

ensure healthy lives and promote well being for all at all ages

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13
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development

A
  • Climate change and food security are the two main areas where we need to work with plants
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14
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development:
food security

A

o Crop yield
 Have been able to increase yield
o By the 2000s had maxed out the yield
o All the while the world’s population id exponentially growing

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15
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development:
climate change: native forests

A

 Native forests contain more carbon than plantations of similar age
 Natural regeneration is a cost-effective way to draw down atmospheric CO2
 Also protect biodiversity
 Forests regulate hydrologic cycles

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16
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development:
climate change: plantation forests

A

 New plantation forests rapidly sequester atmospheric CO2
 Plantations are a source of harvested food products
 With sustainable management and a mixture of native species, plantation forests support critical ecosystem services
 Plantations can support local livelioods and generate income in rural regions

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17
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development:
climate change: harvested wood products

A

 Can substitute fossil based cement, steel, and crude oil products
 Long-lived HWP create an ‘urban’ carbon source
 HWP enhances economic security in local communities especially in rural areas

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18
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development:
climate change: bioenergy

A

 Burning of wood residues from sustainably managed plantations can offset the use of fossil fuels
 Wood residues for bioenergy avoids wasting HWP that would oherwise produce greenhouse gases via decomposition

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19
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development:
plant specific organelles: chloroplasts

A

o Underpinning ecosystems
o Oxygen rich atmosphere

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20
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development:
plant specific organelles: vacuole

A

o Animal and human food

  • starch is contained in double enveloped anyloplasts
    o found in roots, and storage tissue
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21
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development:
plant specific organelles: cellular processes

A

(metabolism)

o Pharmaceuticals
 Medicinal uses
 E.g. Plantago – laxative
 E.g. calendula – anti-tumour properties
o nutraceuticals
 borage – seeds rich in gamma lunolenic acid
 purple viper’s bugloss – seeds eich in okega-3 and 6 fatty acids

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22
Q

PLANT CELL WALL STRUCTURE:
Importance of plant cell development:
plant specific organelles: cell walls

A

food and fuels
- source of fibre
o cell walls are hard to digest
- source of carbon (fuel)
o miscanthus grass: hard to break down
- cellulose is the most abundant organic compound on earth
o is important for plant growth

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23
Q

PLANT CELL WALL STRUCTURE:
what is so special about plant cell walls

A

provides shape

Limits the rate and direction of cell growth

It is a dynamic compartment

Primary and secondary cell wall

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24
Q

PLANT CELL WALL STRUCTURE:
what is so special about plant cell walls
provides shape

A

o Without it we have spherical protoplast

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25
PLANT CELL WALL STRUCTURE: what is so special about plant cell walls - Limits the rate and direction of cell growth
o The flexibility and extensibiloty of the cell wall is what drives plant cell growth and shape changes o Pressures in a plant cell can be 20x that in a car tyre * Turgor pressure o Cell walls contain this pressure o The pressure also plays a role in shape and growth (along with limiting growth)
26
PLANT CELL WALL STRUCTURE: what is so special about plant cell walls dynamic compartment
o Changing throughout the life of the cell
27
PLANT CELL WALL STRUCTURE: what is so special about plant cell walls - Primary and secondary cell wall
o Primary cells are capable of expansion, Need to be able to adapt to the environment  Adhesion between certain cells is maintained by the middle lamella and the cell corners are often filled with pectin rich polysaccharide o Secondary cells build complex structures uniquely suited to the cell’s function
28
PLANT CELL WALL STRUCTURE: what is so special about plant cell walls - highly organised
- It is a highly organised composite of many different polysaccharides and proteins o Sugars are building blocks of the cell wall o Monosaccharides linked into cell wall polymers are derived from glucose o Polymers of specific sugars are further characterised byyteir linkage types and configuration of their carbons o Polymer branching produces great structural diversity
29
PLANT CELL WALL STRUCTURE: what is the principal scaffolding
cellulose
30
PLANT CELL WALL STRUCTURE: cellulose
o Cellulose, a key structural component in plants, is a linear polymer of glucose units linked by β-1,4-glycosidic bonds and stabilized by intermolecular hydrogen bonds between chains, contributing to its strength and insolubility - Accounts for 15-30% of the dry mass of all primary cell walls - Cellulose exists in the form of microfibrils (this is what makes cellulose so strong) - which are para-crystalline assemblies of several dozen (1->4)-b-d-glucan chains hydrogen bonded to one another
31
PLANT CELL WALL STRUCTURE: cellulose microfibrils
- In vascular plants, each microfibril consists of a crystalline core of about 24 chains coated with 12 more that can interact with other glycans and water o 24 in middle, 12 outside - Microfibrils of 36 glucan chains have a theoretical diameter of 3.8 nm - Microfibrils of angiosperms have been measured to be between 5 and 12 nm wide in the electron microscope o Considerable in size!
32
PLANT CELL WALL STRUCTURE: why is cellulose important
- Forestry industry expected to be $998 billion in 2022 - Agricultural industry $12.2 trillion in 2023
33
PLANT CELL WALL STRUCTURE: why is cellulose important application of cellulose microfibres
- Controlled drug delivery - Transdermal drug delivery - Anticancer drug delivery - Antimicrobial drug delivery - Formulation excipients - Hydrogel preparation - Biodegradability - Wound healing dressing - High mechanical strength - High reactive surface area - Skin tissue engineering - Papers - Fibres - Cellophane
34
PLANT CELL WALL STRUCTURE: why is cellulose important novel biofuels
algae
35
PLANT CELL WALL STRUCTURE: other components of the cell wall: carbohydrates
Hemicellulose (xyloglucan) Pectin - The cellulose microfibrils are linked via hemi cellulosic tethers to form the cellulose-hemicellulose network, which is embedded in the pectin matrix
36
PLANT CELL WALL STRUCTURE: other components of the cell wall: proteins
- Proteins can also form networks in the wall - There are three major classes of structural proteins: Hydroxyproline-rich glycoproteins (HRGPs) Proline-rich proteins (PRPs) Glycine-rich proteins (GRPs) - Cell wall proteins (CWPs) can modify cell wall components and customizing them to confer appropriate properties to cell walls o Proteins are key for the functions of the cell wall!
37
PLANT CELL WALL STRUCTURE: take home messages
- Plant science is important - The plant-specific components of cells are of huge relevance - The plant cell wall is formed of cellulose, hemicellulose and pectin - The structure of cellulose and applications o FUNCTION
38
CELL WALL FUNCTION - IMMUNITY first defence
First defence: physical barriers of plant surfaces - Trichomes - Thickened cuticle layers o Rich in oils to avoid contact - Thickened cell wall layers
39
CELL WALL FUNCTION - IMMUNITY first defence: trichomes
- In certain cell types, walls are elaborated to carry out specialized functions - The protoplast disintegrates during development and the mature cell consists of entirely cell wall o Only cell wall on top of the epidermis
40
CELL WALL FUNCTION - IMMUNITY Induced defences: recognition of pathogens
- Microbes are often detected by the host plant at early stages of interaction - Perception is mediated by pattern recognition receptors (PRRs) - PRRs are able to perceive pathogen-associated molecular patterns (PAMPs) - Plants also perceive signalling molecules released for their own cell wall constituents - These signalling molecules are described as damage-associated molecular patterns (DAMPs)
41
CELL WALL FUNCTION - IMMUNITY doubled layered
a doubled layer immune system PAMPs - 1st layer PAMP triggered immunity - 2nd layer
42
CELL WALL FUNCTION - IMMUNITY PRR cell wall defences: ROS
- Reactive oxygen species (ROS) are generated such as superoxide anion and hydrogen peroxide (H2O2) e.g. the generation of ROS in the model grass Brachypodium distachyon in response to attack by the rice blast fungus Magnaporthe oryzae red arrow indicated the appressorium
43
CELL WALL FUNCTION - IMMUNITY roles of H2O2
a ROS: - Toxic to pathogens - Crosslinks host cell wall components to strengthen the barrier against fungal penetration - Acts as a second messenger to turn on defence-related genes
44
CELL WALL FUNCTION - IMMUNITY PRR cell wall defences: Callose rich-papillae
Strengthen the cell wall mechanically to block pathogen penetration. Act as a barrier for toxic compound delivery, concentrating antimicrobials (like ROS, phytoalexins). Help signal downstream immune responses, including gene activation. e.g. deposition of callose in Solanum lycopersicum (tomato) leaves in response to attack by the late blight pathogen Phytophthora infestans
45
CELL WALL FUNCTION - IMMUNITY PRR cell wall defences: Callose rich-papillae role of callose
- Physical barrier to pathogens - Chemical delivery of toxic compounds - Acts as a second messenger to turn on defence-related genes
46
CELL WALL FUNCTION - IMMUNITY role of cell wall in defence
- Some specialised cells provide pre-invasive protection - Fragments of wall polysaccharides may elicit secretion of defence molecules, and the wall may become impregnated with protein and lignin to armour it against invading fungal and bacterial pathogens - Walls contain signalling molecules that participate in cell-cell and wall-nucleus communication
47
CELL WALL FUNCTION - IMMUNITY Microbial modification of the cell wall: how can pathogens modify cell walls
- Modifications of polysaccharides - Modification of pH - Modification of Ca2+
48
CELL WALL FUNCTION - IMMUNITY Microbial modification of the cell wall: - Modifications of polysaccharides
- Pathogens secrete degrading enzymes to loosen cell walls o Expansins and expansin like proteins o Loosenins o Swollenins - Disrupt the interactions between polysaccharides and break them into smaller fragments - Necrotrophs o Kill plant cells o E.g. Botrytis cinerea - Biotrophs o Live from plant cells o E.g. phytopthora infestand (Both degrade plant cell walls)
49
CELL WALL FUNCTION - IMMUNITY Microbial modification of the cell wall: Modification of pH
- Cell wall proteins are pH regulated (e.g expansins) - Changes in pH can result in cell wall loosening as pH influences the binding of cellulose and pectin - Microbial changes of pH can alter cell wall structure to favour colonisation - Modification of pH  impact defence signalling o No such rule for increased or decreased pH between necro and biotrophs
50
CELL WALL FUNCTION - IMMUNITY Microbial modification of the cell wall: Modification of Ca2+
- Pectins (and also cellulose) can bind Ca2 and the binding affects mechanical properties - Ca2+ between pectin strings - Ca2+ ions are some of the first elements in PTI - Some bacterial pathogens can effectively chelate Ca2+ causing the gelification of extracellular polymeric substances that act as “glue” to stick the pathogen to the plant o Ca2+ is also a second messenger for different pathways
51
CELL WALL FUNCTION - IMMUNITY Microbial modification of the cell wall: what communications
- Modification of Ca2+ o Second messenger o PTI Pathogen-cell wall interaction - Plant pathogens cause a loss of turgor on plant cells o More on this to follow
52
CELL WALL FUNCTION - IMMUNITY take home messages
- The plant cell wall is involved in defence against pathogens at different levels - Pathogens can modify cell walls - Plants are not oblivious to the colonisation and use the changesin the cell wall to activate defence mechanisms
53
CELL WALL FUNCTION - GROWTH AND TURGOR General concepts
- Water potential is a measure of the potential energy in water o The potential energy in a system is compared to pure water when both temp and pressure are the same - In other words water potential is the energy required per quantity of water to transport an infinitesimal quantity of water from the sample to a reference pool of pure free water - E.g. salt will make water potential more negative - The water potential o Water will tend to the more negative water potential o (in order to bring a negative water potential closer to 0)
54
CELL WALL FUNCTION - GROWTH AND TURGOR pressure in the cells
- In plant cells the pressure is generated primarily by water within the vacuole o Limit o Energy to blow up comes from the water pressure o But has a limit o Limit will cause cell to pop  This is referred to as elasticity
55
CELL WALL FUNCTION - GROWTH AND TURGOR pressure in the cells: elasticity
* How much you can expand or retract the cell without lysis of the cell  Cell wall needed to be somewat flexible * So the volume of the cell can change
56
CELL WALL FUNCTION - GROWTH AND TURGOR pressure in the cells: cell walls needs to be...
tough enough to withstand pressure but not so tough that the cell cannot grow in change in volume
57
CELL WALL FUNCTION - GROWTH AND TURGOR concept of elasticity
- Elasticity is how much the volume of the cell has changed per unit of change of pressure - When have a cell wall these values are significantly larger because they can withstand higher pressure
58
CELL WALL FUNCTION - GROWTH AND TURGOR primary cell wall: a flexible matrix
Cells walls are made from different molecules: * Mostly cellulose and pectin o These cellulsoe fibres are aligned in specific directions in the cell o These directions determine the elasticity (what direction the elasticity is in)
59
CELL WALL FUNCTION - GROWTH AND TURGOR primary cell wall: a flexible matrix different organisations
- Second image (criss-cross): this organisation allows elasticity in any direction
60
CELL WALL FUNCTION - GROWTH AND TURGOR primary cell wall: why do the fibres retract again
- Pectin - Combination of cellulose giving strength and telling in which direction can expand and pectin determining how much expansion
61
CELL WALL FUNCTION - GROWTH AND TURGOR Expansion: growth or elasticity
How can expansion be held for a long period So cell can grow * Expansin protein o Holds expansion of the cell
62
CELL WALL FUNCTION - GROWTH AND TURGOR expansin protein
- Pectin in between strands of cellulose - Expansin protein separates the pectin - Letting them expand - Then reconnecting in a new place very well regulated
63
CELL WALL FUNCTION - GROWTH AND TURGOR growth direction and shape
- Different direction of cellulose will give different shapes o Pressure also plays a role * The more pressure applied the more the shape will change
64
CELL WALL FUNCTION - GROWTH AND TURGOR growth direction and shape how is this controlled
- Each cell by itself cannot control the direction they grown in o Have cells next to them o The shape of the cell is not defined by itself, it is defined by the cell and the neighbouring cells  How this actually works is still being studied
65
CELL WALL FUNCTION - GROWTH AND TURGOR Microscopic effect of pressure in plant cells
Cells in plants are part of different tissues - Have in common the microscopic effect of the pressure Microscopic effect? - Can measure the pressure change e.g. o Chloroplasts pushed against wall  Better for photosynthesis (exchange) o Turgor used to maintain the structure inside the cell in specific places
66
CELL WALL FUNCTION - GROWTH AND TURGOR Macroscopic effect of pressure in plant cells
- Wilted plant o Plant has loss turgor o Does not have enough pressure to maintain against cell wall o As a consequence all the tissues suffer o How do plants get to this point - but can we study/avoid this - If able to correlate the energy that is required to move water from one place to another with the amount of water that you have o We know the buffer that we have before the plant is under stress
67
CELL WALL FUNCTION - GROWTH AND TURGOR Macroscopic effect of pressure in plant cells pressure volume curve
To get a relationship between pressure and water content: - Why does the plant loose more or less water at different pressures?
68
CELL WALL FUNCTION - GROWTH AND TURGOR Macroscopic effect of pressure in plant cells pressure volume curve: what it tells us
- The intersection point shows the pressure that the cell is projecting against the cell wall is 0 - This is the turgor loss point o When this point is reach it seems that the plant has lost their ability to control how much water is missing o Not just physically important but also biologically important - Can calculate how much the cell changed its volume and how much of that change of volume gives a buffer for the plant
69
CELL WALL FUNCTION - GROWTH AND TURGOR Macroscopic effect of pressure in plant cells pressure volume curve: what can we learn
- Plants experience dry conditions and water-stress by losing turgor - Species with a lower modulus of elasticity have a stiffer cell wall - More negative water pressure is associated with a more drought-resistant species
70
CELL WALL FUNCTION - GROWTH AND TURGOR summary: Cell walls give...
structure and shape to plant cells
71
CELL WALL FUNCTION - GROWTH AND TURGOR summary: Cell wall elasticity...
is fundamental for plant survival and growth
72
CELL WALL FUNCTION - GROWTH AND TURGOR summary: Turgor is the...
pressure generated by the cytosolic and vacuole fluid against the cell wall
73
CELL WALL FUNCTION - GROWTH AND TURGOR summary: Plant cells’ normal state in under...
turgor pressure plants need turogor
74
CELL WALL FUNCTION - GROWTH AND TURGOR summary: There is a direct link between...
cell wall properties and macroscopic effect at the plan level, such as drought tolerance
75

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