Plant Cell - Dalhousie

Plant Cell lectures I - IV

Why are cells small?

They need to have a big cell surface area to cell volume ratio

What does the resolution of a microscope determine?

How close two objects can be and still be seen as two objects (not merged together)

Desribe a light microscope

It uses the beam of light to see objects. Uses glass lenses, resolution around 200nm

Give some examples of light micrsoscopes

• bright field microscope

• phase contrast microscope

• dark field microscope

• differential interference contrast, DIC

• flourescence microscope

• confocal microscope

What is a transgenic plant?

A genetically modified plant wiht a new gene that may import a new function

What is the natural genetic engineer? And how is it used

Agrobacterium tumefaciens is a natural genetic engineer, where the t-DNA (transfer DNA) of the Ti-plasmid can be used to fuse modified genes into the plant’s own genome. The bacteria senses the compound acetosyringone (which the plant releases when wounded) and uses it to infuse the t-DNA and infect the plant.

Where does Agrobacterium tumefaciens originate from?

It is a virus which causes the Crown Gall disease in trees.

What’s callus?

an unorganized and undifferentiated group of cells. stimulated by auxin and cytokinin (more auxin → shoots, more cytokinin → roots)

What’s totipotency?

the ability of one plant cell to develope a whole new plant, with all cell types represented. asexual reproduction.

Give some examples of electron microscopes

• scanning electron microscope

• transmission electron microscope

• laser capture dissertion

• atomic force microscope, AFM

What’s a scanning electron microscope?

An electron microscope uses an electro-magnetic lenses to study surface structures. Resolution 10nm and magnifying up to about 20 000 times

What’s a transmission electron microscope?

An transmission electro-magnetic lense to study ultrastructure. It magnifies images up to about 100 000 times, resultion 2nm.

Describe the tissue preparation for transmission electron microscope

• fixation (preserve a sample of biological material as close to its natural state as possible)

  • primary fixation (glutaraldehyde and paraformaldehyde)

  • post fixation (osmium tetroxide)

• dehydration (get away all of the water in the cell (ethanol or acetone))

• resin embedding (for preserving the sample)

• sectioning (cutting ultrathin sample (ultramicrotome))

• staining (to be able to see the preparate) (uranyl acetate and lead citrate)

Describe laser capture microdissection

A dissection where a laser beam is separating cells of interest from other cells

What’s atomic gorce microscope (SFM)?

A microscope for mapping and measuring surface features of very small objects (with very high-resolution)

What’s the cell theory?

• all organisms are made up of one or more cells

• the cell is the basic unit of structure of all organisms

• all cells arise from pre-existing cells

What’s the differences between an animal and plant cell?

• the cell wall (stronger in plant cells)

• plant cells contain large vacuoles

• plant cells contain plastid chloroplasts

How is the plant cell organised?

• the cell wall surrounds the protoplast

• in the protoplast, there’s the nucleus and cytoplasm

• in the cytoplasm: there is the plasma membrane, endomembrane system, cytosol, organelles and cytoskeleton

Name some organelles in the plant cell

• chloroplast, mitochondria, cytoskeleton, oxelate, vacuole

Describe what a protoplast is

It’s all the living cells in a plant cell, as it is everything that the cell wall contains

What are the different parts of the cell wall?

• middle lamella

• primary cell wall

• secondary cell wall

• plasmodesmata

What’s the difference between cytokinesis in plant cells and animal cells?

In plant cells cytokinesis occurs through the formation of a cell plate, while the animal cells do it through a cleavage furrow. A cell plate is a plate that develops at the midpoint between the two groups of chromosomes in a dividing cell

What’s the phragmoplast?

The organelle that builds the cell plate

Why do plant cells have cell walls?

• turgor pressure

• structural support

• protection

• adaption to terrestrial life

• transport and signaling

• cell adhesion

What does the primary cell wall consist of?

cellulose microfibrils in a matrix

• cellulose

• hemicellulose

• pectins

• proteins

What is the most abundant renewable carbon source on earth?

cellulose

What does hemicellulose consist of?

• polysaccharide

• xylose

• arabinose

• mannose

What does pectin exist of?

• polysaccharides

• polygalacturonic acids

When does the cell wall get rigid?

Once lignin is present. Then the cell dies. This only happens in the secondary cell wall

How is the cell shape of a plant cell determined

The microtubules determine how to deposit the cellulose microfibrils

What’s the cortical microtubulues?

An array of microtubules laying under the plasmamembrane, which determines the shape of the cell

What deposit of cortical microtubules creates and spherical and elongated cell, respectively?

random deposit → spherical shape

vertical deposit → elongated cell

What is lignin?

It’s a class of compolex polymerrs. It adds compressive strength and bending stiffness to the secondary cell wall (cell is dead when lingnin is present). Important for xylem transport!

What is cutin and suberin?

Fatty acid substances that is abundant in the outer protective tissues of the plant. It has portective properties (subrerin) and help reduce the loss of water (suberin and cuterin)

What’s the functions of the cell wall?

• provide tensile strength (keeping cells from rupturing from turgor pressure)

• provide mechanical support

• xylem long distance transport

• cutinized walls to prevent water loss (cutin in cuticle)

• provide insects, pathogens and water loss

• growth development

What is the only organism that can decay lignin?

white rot fungi

What is the middle lamella?

a thin layer between the primary cell walls that glues them together. they mainly consists of pectin.

Compare the tracheary element cell types:

• tracheids: lack perforation plates in end walls, they are intact. the water movement is therefore slower and more narrow, but safer (as water bubbles are confined to one cell

• vessel elements: have perforation plates in the end walls, letting water pass through. this makes the water transportation more faster and more efficient (wider) but also more vulnerable.

What is plasmodesmata?

cytoplasmic channels that connect plant cells (via lack of secondary cell walls). they allow molecules to pass between cells

What is a desmotubule?

a connection (sort of pipe) inside the plasmodesmata which connects the ER from one cell to the ER of the next

What’s the symplast?

the living portion inside the plasma membrane

What’s the apoplast?

The non-living portion outside of the plasma membrane, i.e. the cell wall, the spaces between the cells and the xylem

What’s the apoplastic pathway?

the pathway through non-living parts. much quicker than the symplastic pathway

What’s the symplastic pathway?

the pathway through living-part. much slower, since it must pass through membranes

Describe what the endodermis is and does

The endodermis is a part of the symplastic pathway, and it regulates the flow of substances between the cortex and the vascular tissue

What is a casparian strip?

it’s like a tube that surround four of the six sides of an epidermal cell, and makes the water and minerals to pass across the cell membranes instead of between the cell walls. it’s mainly made of suberin

Which are the structural cell wall proteins and their function?

• glycoproteins

• extensins (pathogen defense, cell-cell recognition, cell adhesion)

what are the different enzymes in the cell wall?

• peroxidases (oxidative enzymes) (lignification and suberization)

• pectinases, cellulases (hydrolytic enzymes)

• expansins (enzymes that catalyse cell wall creep activity)

What are the functional enzymes good for?

• pathogen protection

• cell expansion

• cell wall maturation