PCD, its classes, its function in plants.

1. Programmed cell death in
development and defence...
Made by: SHEETAL MEHLA
2018BS13D
COBS&H, CCS HAU

2. Why do cells commit suicide?
• Cells commit suicide for two different reasons.
• Programmed cell death or PCD is needed for
natural development.
• PCD is also needed to naturally destroy cells if
the body recognises them as a threat to their
system or to maintain the overall integrity of an
organism.

3. PCD (Programmed cell death)
• Programmed cell death is an active,
genetically controlled process leading to
selective elimination of unwanted or damaged
cells in eukaryotes.
• It occur via apoptosis- a Greek word meaning
‘falling leaves’.
• It is essential for growth and development of
multicellular organism as well as proper
response to environment.

5. Morphological changes at cellular level
• Biochemical events lead to characteristic cell
changes (morphology) and death. These changes
include:
• Blebbing
• Cell shrinkage
• Nuclear fragmentation
• Chromatin condensation
• Chromosomal DNA fragmentation
• Global mRNA degradation.

7. NECROSIS APOPTOSIS
Cellular swelling Cellular condensation
Membranes are broken Membranes remain intact
ATP is depleted Requires ATP
Cell lyses, eliciting an inflammatory
reaction
Cell is phagocytosed, no tissue reaction
DNA fragmentation is random or
smeared
Ladder like DNA fragmentation
In vivo whole area of tissue are
affected
In vivo, individual cells appear affected

8. Importance
• Coordination between cell death and
proliferation , growth and differentiation is of
fundamental importance for the maintenance
of tissue and organ homeostasis.

9. Classes of plant PCD
PCD Classes EXAMPLES
AUTOLYTIC Rapid clearance of the cytoplasm also
called as developmental PCD.
PCD that occurs during the formation
of the male and female gametes, in
seeds, embryonic structures, and
during development of roots and
shoot.
NON- AUTOLYTIC In this tonoplast rupture may or may
not be encountered and is not
followed by complete clearance of
the cytoplasm.
Endosperm in cereal seeds.

10. Mechanism of PCD in plants

11. Regulation of PCD in plants
• Plant proteases: metacaspases,
Subtilisin- like serine proteases,
VPE family of proteases.
• Bcl-2 associated athanogene (BAG) family: is an
evolutionary conserved family of co-chaperons in
plants and animals distinguished by a
characteristics BAG domain that mediates direct
interaction with HSP70.
• Hypersensitive mediated PCD: rapid localised
plant cell death upon contact with avirulent
pathogens.

12. Localization of proteases in plants
• Proteolytic enzymes that are involved in PCD
are localized in different compartments of
plant cells:
• Cytoplasm (metacaspases)
• Vacuoles (VPE)
• Intercellular fluid (phytaspases).

13. Plant PCD is associated with a number
of developmental processes including;
• Embryo formation
• Degeneration of aleurone layer during monocot
seed germination
• Differentiation in traceary elements in water
conducting xylem tissue
• Formation of root aerenchyma and epidermal
trichomes
• Anther tapetum degeneration
• Floral organ absession
• Pollen self incompatibility
• Remodelling of some type of leaf shapes and
• Leaf senescence.

14. Programmed cell death also play
important role in providing plant
immunity to biotrophic pathogens

16. PCD in cereals
• The lifecycle of cereal seeds can be divided
into two phases development and
germination, separated by quinicent phase.
• This require growth and differentiation of new
tissue but also the ordered disappearance of
cells which takes place by PCD.

17. • At early stage of seed development, maternal
tissue (nucellar, pericarp and nucellar projection)
undergoes progressive degeneration by PCD.
• At later stage endosperm undergoes
degeneration through PCD but these cells remain
intact in the mature grain and their content will
not be remobilized until germination.
• Aleurone, scutellum remain alive unless their
functioning is required by the seed, at the time
of germination when their function is fulfilled
these also undergo PCD.

18. Role of PCD in development and
germination of seeds

19. Aleurone layer
• In seeds, aleurone cells form a secretary tissue
that releases hydrolases to digest the
endosperm and nourish the embryo.
• When it become unnecessary it finally die.

20. Root cap cells
• Cell death occurs in root caps when roots are
grown, showing that cell death is normal part
of development and not a consequence of
abrasion during soil penetration.
• Shrinks

21. Interaction with environment
• Hypoxia (Oxygen deprivation)
• Cell death can occur in the cortex of the root and
stem base in response to water logging and hypoxia.
• It leads to ROS (H2O2, ethylene).
• Ethylene triggers apoptotic pathway- eliminate some
cells- aerenchyma.
• The internal air spaces generated by cell death
facilitate more efficient transfer of oxygen from
aerial organs to waterlogged stem base and roots.

22. PCD in Xylogenesis
• Autolysis begins as the cytoplasm
and nuclei become lobed, condensed
and shrunken and ends as the
cytoplasm breaks into small packets.

24. Important in embryogenesis and
remodelling shape of leaves.
• Morphogenesis remove excess cells.
• Selection (elimination of non- functional cells).
• Deletion of suspensor cells in embryos.
• Deletion of stamen primordia cells in
unisexual flowers.

26. PCD in embryo development
• The death embryo suspensor requires
activation of autophagy related components
downstream of metacaspase mcIIPa, so its
suppression promotes a switch from PCD to
necrosis.

29. Non autolytic
hypersensitive
response
endosperm of
cereal seeds

30. Hypersensitive response mediated
PCD
• Rapid, localised plant cell death upon contact
with avirulent pathogens. HR is considered to
be a key component of multifaceted plant
defence response to restrict attempted
infection by avirulent pathogens.
• Rapid within 24 hrs.
• It also provide long lasting systemic acquiured
resistance against subsequent attack by broad
range of normally virulent pathogen.

31. Mechanism of Hypersensitive
Response:
• Ion flux (Ca2+ in cytosol)
• Oxidative burst
• Disruption of cell membrane opening of ion
channels
• Cross linking of phenolic with cell wall
components
• Production of anti-microbial phytoalexins and
PR proteins
• Apoptosis

33. Hypersensitive response by bacterial
pathogens
• Bacteria like Pseudomonas syringae inject
effector proteins into plant cells using the
Type III secretion system.
• Plant that are resistant to the bacteria have
resistance proteins that recognize the
effector proteins and cause the infected cells
to commit suicide to prevent the bacteria
from infecting rest of the plant.

35. Endosperm of cereal seeds
• In wheat seeds, the expansion of the endosperm
is preceded by PCD in cells adjacent to the
nucellar projections.
• The endosperm cavity is thus formed, allowing
the transfer of nutrients from the vascular bundle
embedded in the pericarp to the growing
endosperm.

36. References
• Martin B. et. al., (2013): Centrality of Host Cell Death in Plant- Microbe
Interactions. Annual Review of Phytopathology.2013.51:543-70
• Domínguez, F., & Cejudo, F. J. (2014). Programmed cell death (PCD): an
essential process of cereal seed development and germination. Frontiers
in plant science, 5, 366.
• Drew, M. C., He, C. J., & Morgan, P. W. (2000). Programmed cell death and
aerenchyma formation in roots. Trends in plant science, 5(3), 123-127.
• Neill, S. (2005). NO way to die–nitric oxide, programmed cell death and
xylogenesis. New Phytologist, 165(1), 5-8.
• Reape, T. J., Molony, E. M., & McCabe, P. F. (2008). Programmed cell death
in plants: distinguishing between different modes. Journal of Experimental
Botany, 59(3), 435-444.