PCD in Plant Development

Question 1

What are the differences between animal cells and plant cells?

Answer 1

cell wall,
plastids,
large vacuole

Question 2

What are the types of cell death?

Answer 2

programmed cell death & necrosis

Question 3

How do PCD and necrosis differ in terms of their mechanism and the energy they require?

Answer 3

PCD is genetically encoded & active process;

necrosis is accidental & passive process

Question 4

What is necrosis a side effect of?

Answer 4

injury

Question 5

What is frost bite damage an example of?

Answer 5

necrosis

Question 6

What are the characteristics of PCD (apoptosis)?

Answer 6

physiological cell death,
membrane blebbing (but no loss of integrity),
condensation of chromatin,
formation of membrane-bound bodies (apoptic bodies),
no mitochrondrial swelling,
DNA laddering,
phagocytosis,
no inflammation

Question 7

What are the characteristics of necrosis?

Answer 7

accidental cell death,
loss of membrane integrity,
flocculation of chromating,
swelling of the cell and lysis,
mitochrondrial swelling,
no DNA laddering,
phagocytosis,
inflammation

Question 8

What is tissue remoeling (vertebrate limb bud development) an example of?

Answer 8

apoptosis in animal cells

Question 9

What does apoptosis allow the elimination of, with examples?

Answer 9

unwanted cells (e.g. tumor cells),
transitory organs and tissues (e.g. pronephors in higher vertebrates),
cells that have completed their function (e.g. tail of tadpole)

Question 10

What happens in humans if PCD does not take place during vertebrate limb bud development?

Answer 10

fingers would stick together

Question 11

What is Caenorhabditis elegans?

Answer 11

a model organism for studying the coe machinery involved in PCD

Question 12

Why is Caenorhabditis elegans so handy fr studying PCD?

Answer 12

exactly 131 cells undergo PCD at precisely defined times and locations

Question 13

What are ced-3, ced-4, ced-9, and Egl-1?

Answer 13

4 proteins that are central to the execution of the death program in Caenorhabditis elegans

Question 14

What are some techniques used to detect apoptosis?

Answer 14

agarose gel electrophoresis,
in situ DNA end-labelling,
light and electron microscopy,
assay systems

Question 15

How does agarose gel electrophoresis detect apoptosis?

Answer 15

can see fragmented DNA (characteristic of PCD)

Question 16

How does in situ DNA end-labelling detect apoptosis?

Answer 16

can identify fragmented DNA (characteristic of PCD)

Question 17

How does light and electron microscopy detect apoptosis?

Answer 17

look for morphological changes

Question 18

How do assay systems detect apoptosis?

Answer 18

identify Caspase family proteins

Question 19

How many techniques must be used to reliably detect apoptosis?

Answer 19

2

Question 20

What are some processes of plant development in which PCD is very important?

Answer 20

embryogenesis,
xylem differentiation,
aerenchyma formation,
shedding of root cap cells,
leaf morphogenesis,
hypersensitive cell death,
leaf senescence

Question 21

When does PCD take place during plant development?

Answer 21

from fertilization to complete death of plant (leaf senescence)

Question 22

What does a comparison of the mechanisms and molecules of PCD between the plant and animal kingdoms suggest?

Answer 22

common evolutionary origin

Question 23

What applications are there for PCD research?

Answer 23

agriculture and horticulture

delay senescence - food would last longer

Question 24

What is xylem?

Answer 24

the supporting and water-conducting tissue of vascular plants?

Question 25

How does PCD function during xylem differentiation?

Answer 25

entire contents of cells undergo PCD; cell wall left intact (multiple stack to make a tube)

Question 26

What process is the "pulling source" that allows the transportation of water up against gravity?

Answer 26

transpiration (evaporation of water)

Question 27

What keeps the water column in xylem intact?

Answer 27

hydrogen bonds

Question 28

What are aerenchyma and how are they formed?

Answer 28

gas spaces in the root cortex; | caused by the controlled collapse and death of certain cortical cells

Question 29

What are aerenchyma used for?

Answer 29

storing oxygen/allowing gas exchange

Question 30

What is the primary difference between the PCD in xylem differentiation and the PCD in aerenchyma formation?

Answer 30

cell wall left intact in xylem; | everything including cell wall undergoes PCD in aerenchyma

Question 31

What is the function of the root cap cells?

Answer 31

to protect the root apical meristem during germination and growth

Question 32

Why are root cap cells continually displaced by new cells?

Answer 32

they're easily damaged by the soil so they die often

Question 33

What is the apical meristem?

Answer 33

tissue found in the tips of roots in plants; | begins growth of new cells at the tips of roots

Question 34

How is PCD involved with root cap cells?

Answer 34

root cap cells are killed to be replaced by new cells (?)

Question 35

What induces hypersensitive cell death (HR) and why?

Answer 35

certain plant pathogens and involved PCD; | to restrict the spread of pathogens from infected sites

Question 36

What is leaf senescence?

Answer 36

the final stage of leaf development | browning... chlorophyll degrading...

Question 37

What is an example of an abiotic externally induced PCD, and what is the abiotic factor that causes it?

Answer 37

aerenchyma formation; | low oxygen

Question 38

What is an example of a biotic eternally-induced PCD, and what is the biotic factor that causes it?

Answer 38

hypersensitive cell death; | pathogen

Question 39

What are examples of developmentally regulated PCD?

Answer 39

xylem differentiation, | leaf morphogenesis

Question 40

What is leaf morphogensis?

Answer 40

hole formation in leaves

Question 41

What are the only 2 vascular plants that form holes in their leaves as part of their normal development, and where do they live?

Answer 41

``` Monstera obliqua ("swiss cheese plant"); land plant, Aponogeton madagascariensis ("lace plant"); aquatic plant ```

Question 42

How was PCD identified as being part of leaf morphogenesis in Monstera obliqua?

Answer 42

DNA fragmentation in gel electrophoresis; tunel assay to detect dying nuclei

Question 43

What colours do the lace plant appear throughout development and why?

Answer 43

early stage: red leaves (pigment anthocyanin dominates); | later (after cell death): green leaves (anthocyanin disappears as leaf matures, leaving chlorophyll)

Question 44

What are the five stages of leaf development in the lace plant?

Answer 44

1. tissue pattern formation 2. window 3. perforation formation 4. performation expansion 5. mature

Question 45

What can be seen during the tissue pattern formation in lace plants?

Answer 45

no signs of cell death

Question 46

What can be seen during the window formation in lace plants?

Answer 46

clear cells

Question 47

What can be seen during perforation formation in lace plants?

Answer 47

disappearance of organelles

Question 48

What happens during perforation expansion in lace plants?

Answer 48

holes expand in size 10+ times as leaf matures

Question 49

What can be seen in mature perforations in leaf plants?

Answer 49

holes end 4-5 cells from vein

Question 50

Where does PCD start and stop in lace plants during leaf morphogensis?

Answer 50

starts in centre; | stops 4-5 cells from vein

Question 51

Why are lace plants better model organisms to study developmental PCD in than Monstera?

Answer 51

we know when and where cells undergo PCD & transparent aquatic leaves good for microscopy; don't know where in Monstera

Question 52

What pigment/antioxidant may play a role in PCD and how do we know this?

Answer 52

anthocyanin; | PCD only occurs in lace plant leaves that contain anthocyanin

Question 53

Why are special conditions needed to prevent bacterial growth when growing lace plant on MS medium in the lab?

Answer 53

medium has a ton of nutrients for the plant

Question 54

What is the main role of anthocyanin and other accesory pigments in most plants?

Answer 54

to protect the chlorophyll II