The document discusses various types of programmed cell death (PCD), including apoptosis, autophagy, paraptosis, autoschizis, oncosis, and necrosis. It provides details on the characteristics and mechanisms of apoptosis and autophagy. Apoptosis involves blebbing, cell shrinkage, nuclear fragmentation, and is mediated by caspases through the intrinsic and extrinsic pathways. Autophagy results in autophagosomic-lysosomal degradation of cytoplasmic contents and organelles. The document also discusses some plant-specific features of apoptosis and its role in pollen self-incompatibility.

1. Prepared by:-
Kalpataru Nanda
1st
yr M.Sc.(Ag)
Adm. No. - 03PBG/16
Submitted to:-
Dr. Manasi Dash
Jr. breeder
(AICRP On Sesamum)

2. Apoptosis – Programmed Cell Death
History
The concept of "programmed cell-death" was used by Lockshin &
Williams in 1964 in relation to insect tissue development, around
eight years before "apoptosis" was coined. Since then, PCD has
become the more general of these two terms.
PCD has been the subject of increasing attention and research
efforts. This trend has been highlighted with the award of the
2002 Nobel Prize in Physiology or Medicine to Sydney Brenner (
United Kingdom), H. Robert Horvitz (US) and John E. Sulston (UK).

3. Types(cell deaths)
Apoptosis or Type I cell-death.
Autophagic or Type II cell-death.
Apoptosis
 Apoptosis is the process of programmed cell death (PCD) that occur in
multicellular organisms induced by a tightly regulated suicide program,
Controlled by specific genes.
 Biochemical
events lead to characteristic cell changes (morphology) and death.
These changes include blebbing, cell shrinkage, nuclear fragmentation,
chromatin condensation, and chromosomal DNA fragmentation.
 Cell is stimulated by certain factors and it leads to DNA fragmentation of 180
base pairs long (characteristic of apoptosis), intracellular organelles undergo
fragmentation including nucleus and the cell collapses producing blebs and
membranous vesicles pop out of the cell surface.
 When they are budded off they are recognized and engulfed by
macrophages and consumed.

5. Autophagy
 Macroautophagy, often referred to as autophagy, is a catabolic process
that results in the autophagosomic-lysosomal degradation of bulk
cytoplasmic contents, abnormal protein aggregates, and excess or
damaged organelles.
 Autophagy is generally activated by conditions of nutrient deprivation but
has also been associated with physiological as well as pathological
processes such as development, differentiation , neurodegenerative
diseases, stress, infection and cancer.
Paraptosis
 Cells swell, develop large bubbles or vacuoles with liquid inside
and die; this method of suicide is called parapoptosis.
 They don’t employ Caspases, which is hallmark of apoptosis.
This method or most similar methods have been observed in
yeast cells.

6. Autoschizis
• It is a bizarre type of death. Cells develop crates inside and cell organelles
escape from the cell and they are destroyed by some proteases that develop
inside the cell.
• This happens when cancerous cells are treated with Vitamin-C and K. Normal
cells remains unaffected, but substantial number of cancer cells die by
autoschizis.
• There is diminution in cell size, the nuclei become smaller and contain large
nucleoli, which become round and compact. Before it dies, the size of the
resultant autoschizic cell becomes much smaller than the tumor cell from which
it originated.
Oncosis
• Cells expand by taking in lot of water in an uncontrolled manner. Soon
proteins become denatured like cooked yolk proteins, then cells take excess
calcium into cells and death follows.
• Oncosis being ATP independent and does not require mitochondrial function
to proceed. While apoptosis is ATP dependent and requires a degree of
mitochondrial function during the apoptotic process.

7. Necrosis
Cells get injured, cells get punctured where cells lyse extruding
various injurious components, which cause severe damage to
other neighboring cells, causing a widespread destruction; this is
like carnage.

9. Death by Injury vs. Death by Suicide
(Necrosis vs. Apoptosis)

12. Apoptosis – Programmed Cell Death
Why? Developmental (digitation ,metamorphosis in amphibian)
Protective (destroy cells that are a threat)
infected with virus
turn off immune response
DNA damaged cells
cancer

13. What makes a cell commit suicide?
 withdrawal of positive signals (growth factors, Il-2)
 receipt of negative signals (increased levels of oxidants,
DNA damage via X-ray or UV light, chemotherapeutic drugs,
accumulation of improperly folded proteins(stress to E.R), death
activators such as: TNF-a, TNF-b, Fas/FasL)

14. Steps in apoptosis:
1. the decision to activate the pathway;
2. the actual "suicide" of the cell;
3. engulfment of the cell remains by specialized immune cells
called phagocytes;
4. degradation of engulfed cell. (This facilitates prompt clearance
before they undergo secondary necrosis. Dead cells disappear
without a trace and do not produce inflammation)
The actual steps in cell death require:
 condensing of the cell nucleus and breaking it into pieces
 condensing and fragmenting of cytoplasm into membrane
bound apoptotic bodies;
 breaking chromosomes into fragments containing multiple
number of nucleosomes (a nucleosome ladder)

16. Mechanism
Apoptosis Triggered via Two main signaling Pathways
 Intrinsic or mitochondrial pathway
 Extrinsic or death receptor pathway
• Cells contain intrinsic death and survival signals that are genetically regulated.
• The extrinsic pathway is activated in response to multiple external pro-
apoptotic signals, including endogenous Apo2L/TRAIL and other pro-apoptotic
receptor agonists (PARAs)
• The intrinsic pathway is activated by cellular developmental cues or as a
result of severe cellular stress (eg, DNA damage).
• Both pathways induce cell death by activating caspases, which are proteases,
or enzymes that degrade proteins. The two pathways both activate initiator
caspases, which then activate executioner caspases, which then kill the cell by
degrading proteins indiscriminately.
• Caspases (cysteine-aspartic-acid-proteases) are conserved across species.
Synthesized as inactive precursors; activated by proteolytic cleavage.

18. TRDD= TNF receptor associate death domain.
RIP= Receptor interacting protein.
TRAF = TNF receptor associated factor.
TRAIL = TNF related apoptosis inducing ligands.
Tumor Necrosis Factor (TNF)

19. Intrinsic -Mitochrondrial pathway
• Increased mitochondrial permeability with release of pro-apoptotic
molecules into the cytoplasm (cytochrome c).
• Synthesis of anti-apoptotic molecules (Bcl-2) promoted by Growth factors.
• When cells are deprived of growth factors or subjected to stress
antiapoptotic molecules (Bcl-2) are lost.
• Mitochondrial membrane becomes permeable and proteins that activate
caspase leak out.
Extrinsic (Death receptor initiated) pathway
• Death receptors are members of the tumor necrosis factor receptor family
and a related protein called Fas (CD95).
• These molecules contain a death domain.

25. Apoptosis in plants: specific features
• Apoptosis is an integral part of plant ontogenesis; it is controlled
by cellular oxidative status, phytohormones, and DNA methylation.
• In wheat plants apoptosis appears at early stages of
development in coleoptile and initial leaf of 5-6 days old
seedlings.
Distinct ultrastructural features of apoptosis observed are :
(1). compaction and vacuolization of cytoplasm in the apoptotic
cell,
(2).specific fragmentation of cytoplasm and appearance in the
vacuole of unique single-membrane vesicles containing active
organelles,
(3). cessation of nuclear DNA synthesis,
(4). condensation of chromatin in the nucleus,
(5). internucleosomal fragmentation of nuclear DNA, and
(6). intensive synthesis of mitochondrial DNA in vacuolar vesicles.

26.  Peroxides, abscisic acid, ethylene releaser ethrel, and DNA
methylation inhibitor 5-azacytidine induce and stimulate apoptosis.
 Modulation of the reactive oxygen species (ROS) level in seedling by
antioxidants and peroxides results in tissue-specific changes in the
target date for the appearance and the intensity of apoptosis.
 Antioxidant butylated hydroxytoluene (BHT) reduces the amount of
ROS and prevents apoptosis in etiolated seedlings, prolongs coleoptile
life span, and prevents the appearance of all apoptotic features
mentioned.
 In roots of etiolated wheat seedlings, BHT induces differentiation of
plastids with the formation of chloro(chromo)plasts.
 Therefore, ROS controlled by BHT seems to regulate mitosis, trigger
apoptosis, and control plastid differentiation and the organization of
various cellular structures formed by endocytoplasmic reticulum.

27. PCD in pollen prevents inbreeding
During pollination, plants enforce self-incompatibility (SI) as an
important means to prevent self-fertilization.
 Research on the corn poppy (Papaver rhoeas) has revealed
that proteinsin the pistil on which the pollen lands, interact with
pollen and trigger PCD in incompatible (i.e., self) pollen.
 The researchers, Steven G. Thomas and Veronica E. Franklin-
Tong, also found that the response involves rapid inhibition
of pollen-tube growth, followed by PCD