PCD in Plant Development Flashcards
What are the differences between animal cells and plant cells?
cell wall,
plastids,
large vacuole
What are the types of cell death?
programmed cell death & necrosis
How do PCD and necrosis differ in terms of their mechanism and the energy they require?
PCD is genetically encoded & active process;
necrosis is accidental & passive process
What is necrosis a side effect of?
injury
What is frost bite damage an example of?
necrosis
What are the characteristics of PCD (apoptosis)?
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
What are the characteristics of necrosis?
accidental cell death, loss of membrane integrity, flocculation of chromating, swelling of the cell and lysis, mitochrondrial swelling, no DNA laddering, phagocytosis, inflammation
What is tissue remoeling (vertebrate limb bud development) an example of?
apoptosis in animal cells
What does apoptosis allow the elimination of, with examples?
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)
What happens in humans if PCD does not take place during vertebrate limb bud development?
fingers would stick together
What is Caenorhabditis elegans?
a model organism for studying the coe machinery involved in PCD
Why is Caenorhabditis elegans so handy fr studying PCD?
exactly 131 cells undergo PCD at precisely defined times and locations
What are ced-3, ced-4, ced-9, and Egl-1?
4 proteins that are central to the execution of the death program in Caenorhabditis elegans
What are some techniques used to detect apoptosis?
agarose gel electrophoresis,
in situ DNA end-labelling,
light and electron microscopy,
assay systems
How does agarose gel electrophoresis detect apoptosis?
can see fragmented DNA (characteristic of PCD)
How does in situ DNA end-labelling detect apoptosis?
can identify fragmented DNA (characteristic of PCD)
How does light and electron microscopy detect apoptosis?
look for morphological changes
How do assay systems detect apoptosis?
identify Caspase family proteins
How many techniques must be used to reliably detect apoptosis?
2
What are some processes of plant development in which PCD is very important?
embryogenesis, xylem differentiation, aerenchyma formation, shedding of root cap cells, leaf morphogenesis, hypersensitive cell death, leaf senescence
When does PCD take place during plant development?
from fertilization to complete death of plant (leaf senescence)
What does a comparison of the mechanisms and molecules of PCD between the plant and animal kingdoms suggest?
common evolutionary origin
What applications are there for PCD research?
agriculture and horticulture
delay senescence - food would last longer
What is xylem?
the supporting and water-conducting tissue of vascular plants?
How does PCD function during xylem differentiation?
entire contents of cells undergo PCD; cell wall left intact (multiple stack to make a tube)
What process is the “pulling source” that allows the transportation of water up against gravity?
transpiration (evaporation of water)
What keeps the water column in xylem intact?
hydrogen bonds
What are aerenchyma and how are they formed?
gas spaces in the root cortex;
caused by the controlled collapse and death of certain cortical cells
What are aerenchyma used for?
storing oxygen/allowing gas exchange
What is the primary difference between the PCD in xylem differentiation and the PCD in aerenchyma formation?
cell wall left intact in xylem;
everything including cell wall undergoes PCD in aerenchyma
What is the function of the root cap cells?
to protect the root apical meristem during germination and growth
Why are root cap cells continually displaced by new cells?
they’re easily damaged by the soil so they die often
What is the apical meristem?
tissue found in the tips of roots in plants;
begins growth of new cells at the tips of roots
How is PCD involved with root cap cells?
root cap cells are killed to be replaced by new cells (?)
What induces hypersensitive cell death (HR) and why?
certain plant pathogens and involved PCD;
to restrict the spread of pathogens from infected sites
What is leaf senescence?
the final stage of leaf development
browning… chlorophyll degrading…
What is an example of an abiotic externally induced PCD, and what is the abiotic factor that causes it?
aerenchyma formation;
low oxygen
What is an example of a biotic eternally-induced PCD, and what is the biotic factor that causes it?
hypersensitive cell death;
pathogen
What are examples of developmentally regulated PCD?
xylem differentiation,
leaf morphogenesis
What is leaf morphogensis?
hole formation in leaves
What are the only 2 vascular plants that form holes in their leaves as part of their normal development, and where do they live?
Monstera obliqua ("swiss cheese plant"); land plant,
Aponogeton madagascariensis ("lace plant"); aquatic plantHow was PCD identified as being part of leaf morphogenesis in Monstera obliqua?
DNA fragmentation in gel electrophoresis; tunel assay to detect dying nuclei
What colours do the lace plant appear throughout development and why?
early stage: red leaves (pigment anthocyanin dominates);
later (after cell death): green leaves (anthocyanin disappears as leaf matures, leaving chlorophyll)
What are the five stages of leaf development in the lace plant?
- tissue pattern formation
- window
- perforation formation
- performation expansion
- mature
What can be seen during the tissue pattern formation in lace plants?
no signs of cell death
What can be seen during the window formation in lace plants?
clear cells
What can be seen during perforation formation in lace plants?
disappearance of organelles
What happens during perforation expansion in lace plants?
holes expand in size 10+ times as leaf matures
What can be seen in mature perforations in leaf plants?
holes end 4-5 cells from vein
Where does PCD start and stop in lace plants during leaf morphogensis?
starts in centre;
stops 4-5 cells from vein
Why are lace plants better model organisms to study developmental PCD in than Monstera?
we know when and where cells undergo PCD & transparent aquatic leaves good for microscopy;
don’t know where in Monstera
What pigment/antioxidant may play a role in PCD and how do we know this?
anthocyanin;
PCD only occurs in lace plant leaves that contain anthocyanin
Why are special conditions needed to prevent bacterial growth when growing lace plant on MS medium in the lab?
medium has a ton of nutrients for the plant
What is the main role of anthocyanin and other accesory pigments in most plants?
to protect the chlorophyll II
