Programmed cell death, Aging, and Senescence in plants

1
Programmed cell death, Aging, and Senescence in
plants

• I have lived long enough my way of life
• Is falln into the sear, the yellow leaf
• Macbeth Act V, Scene III

April 11, 2012
2
(No Transcript)
3

• Life is not easy for any of us. But what of
  that?
• We must have perseverance and above all
• confidence in ourselves. We must believe that we
  
• are gifted for something and that this thing
  must
• be attained.
• Marie Curie (1867-1934)
• Two Nobel Prizes in the area of physics
  and chemistry.

4
Publication date 2007, April
5
(No Transcript)
6

• OUTLINE
• (1) Programmed cell death (PCD) and senescence
• (stay green mutant).
• (2) Types of plant senescence
• whole plant, tissue (flower, leaf, and fruit),
  cells and organelles (chloroplast).
• (3) Molecular biological approach to study leaf
  
• senescence (use leaf as an example).
• (4) Deciphering the complicated network of
  plant senescence
• exogenous factors abiotc and biotic
  stress, nutrients
• endogenous factors plant hormones
• (5) Different types of PCD in plant. (trachery
  element formation (xylogenesis), aleurone cells
  death, and arenchyma formation in root).
• (6) HR (Hypersensitive response) in plants

7

• QUESTIONS
• 1. Why is senescence necessary? Is senescence
  a positive or negative value for survival,
  evolution and recycling in plants life?
• 2. Why study senescence? (stay green, and
  post-harvest physiology)
• 3. What are the difference and similarity in
  the control of senescence between animals and
  plants?
• 4. Is program cell death (PCD) a general
  phenomenon in plants life cycle? How is
  senescence related to PCD?
• 5. What are the general factors (intrinsic
  and external) that cause senescence?
• (Internal factors reproduction, plant
  growth regulators, physical constraints, shading,
  External factors day length and light flux,
  temperature, water and mineral relations,
  pathogen attack).

8

• 6. What is our current understanding of tissue
  (leaf, fruit
• and seed) senescence?
• (Morphological, biochemical, molecular
  biological, genetically approach)
• 7. What is our current understanding of
  organelle senescence?
• (Chloroplast, mitochondria, peroxysomes,
  ER, nuclei, and vacuole)
• 8. What is our current understanding of
  senescence at the molecular level?
• (Pigments, proteins, lipids, DNA/ RNA).
• 9. What is the molecular mechanism of
  senescence? Is there a common pathway or shared
  component in the process of senescence?
• (Initiation, threshold, reversibility,
  factors interaction, senescence-related genes)

9

• 10. What are the examples of PCD in the
  development of
• plants and plant response to stress? What
  are the
• relationship among growth, differentiation,
  stress and
• senescence?
• (TE element formation, cereal aleurone
  layer, arenchyma
• formation, HR response etc.)
• 11. What are the future questions and future
  directions for
• PCD research?

10
I. Developmental and physiological significance
of senescence

• Senescence
• A program in which the function of organ or whole
  plant naturally
• declines to death. This is an essential phase of
  the growth and
• development in plant. Senescence can occur at
  different levels cell,
• tissue, organs and whole plant.
• Senescence of individual organs such as, leaves
  allow for the
• recovery of most of the nutrients within
  them and their
• relocation to other areas of plant,
  providing a considerable
• energy saving to the plant as whole.
• 2. Senescence may improve the
  efficiency of the plant by removing
• organs which are no longer
  functioning optimally, such as shaded
• lower leaves, and replacing them
  with organs better suited to the
• prevailing condition.

11
Agronomical and Horticultural importance of
senescence

• 1. Annual, biannual (monocarpic), and perennial
  (polycarpic) crops.
• 2. stay-green traits.
• 3. post-harvest physiology.

12
II. Types of plant senescence
Whole plant

• (1) Overall Senescence
• Senescence occurs in whole plant body, such as
  annuals which senesces to death after flower and
  setting.

13

• (2) Top Senescence
• The part aboveground dies with the end of
  growth season,but the part underground is alive
  for several years..
• Perennial weeds , corm(??) and
• bulb(??)lily ?

In summer
In winter
14

• (3) Deciduous senescence
• The leaf falls in specious
• season, in summer or winter.
• Deciduous trees.

15

• (4) Progressive senescence
• Senescence only occurs in older organ or
  tissue.New organ or tissue develops while old
  those are senescing. Green trees?

16
Types of plant senescence (Tissues)
17
(No Transcript)
18
Science 323, 262-265 (2009)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
How do the cells perceive and respond to death
signals, or, put more teleological, how do they
know when to die? (the molecular events that
initiate senescence?)
How do the cells perceive and respond to death
signals, or, put more teleologically, how do
they know when to die? (the molecular events
that initiate senescence?)
23
Leaf-senescence is accepted as a highly
regulated, active process that can lead to
programmed cell death (PCD).
24
Annu. Rev. Plant Biol. 2007. 5811536
25
(No Transcript)
26
Ethylene production of petunia flower after
pollination
27
Programmed Cell Death in Floral Organs How and
Why do Flowers Die?
Annals of Botany 97 309315, 2006
28
(No Transcript)
29
Annals of Botany 97 309315, 2006
30
(No Transcript)
31
What is the role of sugar in petal senescence?

• 1. sugar starvation is the direct cause of leaf
• senescence.
• 2. an increase (sugar accumulation) rather
• than a decrease in sugar levels induces
• leaf senescence.

32
Hypothetical schemes of the relationship between
maturation, sugar starvation, mobilization, and
cell death during petal senescence. In these
schemes, cell death is a result of mobilization
of proteins, carbohydrates, and lipids.
premature senescence
Three conceivable signals for mobilization
maturation, starvation, and sugar accumulation.
33
Is Petal Senescence Due to Sugar Starvation?
34
(No Transcript)
35
(No Transcript)
36
Ethylene production and the expression of
ethylene-induced genes in ripening tomato fruit
B Bracker
Climacteric vs. Non-climacteric fruity
37
Effect of ethylene on tomato fruit formation
Exogenously added ET
never ripe
ein
Exogenously added ET
ein
38
Ethylene synthesis by leaves of control (blue) or
antisense (red) tomato plants expressing ACC
synthase
39
Postharvest biotechnology development on
Vegetables and Fruits
40
Three main morphotypes of programmed cell death
in animals and plants
Types of plant senescence (cellular level)

• 1. Apoptosis
• (1) DNA appears marginalized on the nuclear
  envelope
• (pyknosis) and is fragmented to
  nucleosomal-sized lengths.
• (2) The nucleus and cytoplasm are fragmented
  into vesicles.
• (3) Macrophages remove the corpse in vivo.
• 2. Autophagic or cytoplasmic degenerative PCD
• Consumption of cytoplasm by autophagic
  organelles. May
• or may not display nuclear degradation and
  pyknosis, and usually does
• not involve the participation of
  macrophages.
• 3. lysosomal degenerative PCD
• general loss of cytoplasm without the clear
  involvement of an organelle
• or another cell.

41
Several types of cell death
42
DNA cleavage in apotopsis cell and the terminal
deoxynucleotidyl transferase (TdT)-mediated dUTP
nick end in situ labeling (TUNEL) method
43
Plant Physiology, May 2009, Vol. 150, pp. 217228
44
(No Transcript)
45
(No Transcript)
46
Caspase signaling
Caspase Cysteine protease with aspartate
specificity
47
(No Transcript)
48

• Types of plant senescence (Organelles)
• 1. Chloroplast
• Chloroplasts are one of the earliest sites of
  catabolism in leaf senescence.
• Senescent chloroplasts is different from
  chromoplasts, though in terms of pigment
  composition both of them look very similar.
• Senescent chloroplasts (Gerontoplasts)dev
  elop only from mature chloroplasts, can not
  divide, do not retain any biosynthetic activity
  and have lost their own DNA.
• (c) morphological changing
• increase in the number and diameter of
  osmiophilic globuli (plastoglobuli), loosening
  and disorientation of the granna and dialation of
  the thylakoids, reduced in the density of
  ribosomes and finally size.

49
(No Transcript)
50
Chlorophyll breakdown process
51
(No Transcript)
52
Trends in Plant Science Vol.14 No.3
53
Stay-green mutants have been classified into five
groups, A through E, using both temporal and
biochemical Characteristics.
54
(No Transcript)
55

• 2. Mitochondria
• (a) Mitochondria remain to be intact until a
  very late stage of senescence.
• (b) The respiration rate is generally increased
  during the late stage of senescence. Ex The low
  respiration quotient (RQ), 0.63, is found in 2
  days after the induction of senescence in barley
  leaf segments. This indicates that fatty acids
  may be a major respiratory substrate for
  senescence.
• (c) The activity of the mitochondrial enzyme
  glutamate dehydrogenase has been shown to peak
  late in the senescence of wheat flag leaves.

56
(No Transcript)
57

• 3. Peroxisomes
• (a) During senescence, peroxisomes are
  active in purine catabolism, glyoxylic acid cycle
  and photorespiration.
• (b) Glyoxysomes and leaf peroxisomes are
  interconverted during the development and
  senescence of oil-storing rape cotyledons.
• (c) During senescence, two key enzymes
  involved in the glyoxylate cycle, isocitrate
  lyase and malate synthase, are induced, as well
  as uricase which participated in the breakdown of
  RNA.

58

• 4. Endoplasmic reticulum and vacuole
• (a) As senescence progress, phospholipid
  declines in a coordinated way in rough and smooth
  ER.
• (b) Vacuoles are the last and involved in the
  final stages of chlorophyll breakdown during
  senescence.
• VPE (vacuole processing enzymes----capasaes
  -like enzyme)

59
IV. Molecular biological approach to study leaf
senescence
60
How is leaf senescence assayed?

• As with any other biological phenomena, it was
  critical to develop
• an accurate and proper assay for leaf senescence.
  Two main
• points must be seriously considered in analyzing
  leaf senescence.
• First, leaf senescence should be measured on a
  single leaf base
• along with its age information. Measuring
  senescence parameters
• with a mixture of several leaves at a given age
  of a plant is not a
• valid analysis for leaf senescence because the
  individual
• leaves of a plant have different ages.
• Second, the senescence symptom should be
  measured with
• various senescence parameters and ideally with
  markers that
• cover various aspects of senescence physiology.
  Senescence
• results from a sum of various physiological
  changes and it is
• often possible that a single parameter may not
  reflect senescence
• but only the change of a specific physiology
  related to the
• measuring parameter.

61

• Many parameters must be assayed when looking at
  leaf senescence as many processes are known to be
  involved.
• Only single leaves can be measured, as senescence
  is age related different leaves on the same
  plant will be of different ages.
• a. Leaf Yellowing, a sign of mesophyll
  cell senescence
• b. Photochemical efficiency
• c. Expression of photosynthetic related
  genes
• (RuBisco, LHCP, Chla/or b(CAB))
• d. Ion leakage
• e. Chlorophyll content
• f. Protein levels
• (total protein amount, NH4
  accumulation)
• g. Expression of known senescence
  stimulated genes (SAG)
• h. Expression of senescence stimulated
  enzymes
• (DNase, RNase, protease,peroxidase
  etc.)
• i. DNA fragmentation (TUNEL assay)

62
(No Transcript)
63
(No Transcript)
64
Journal of Experimental Botany, Vol. 48, No. 307,
pp. 181-199, February 1997
65
mRNA expression during leaf development
66
LSC54, LSC222 LSC25
LSC7,LSC210 LSC212,LSC460 LSC94 LSC550,
LSC680 LSC8, LSC101
67
To reveal the molecular mechanism of initiation
and progression of leaf senescence by analysis of
the modes of regulation of SAGs
(senescence-associated genes) -- Class I
Housekeeping genes control essential metabolic
activities of the cell and
expressed at a constant level through the life of
leaf. (not specific to
senescence) -- Class II and III Genes
expressed at green leaf stage. Genes are active
well before senescence starts and
switched off before any sign of
senescence. Class III genes may
encode proteins that cause the
initiation of senescence by
their absences. -- Class IV Regulatory genes
expressed immediately prior to or at the onset
of senescence and expressed for a relative
short time only. -- Class V Genes involved in
the mobilization processes that occur
specifically during senescence. -- Class VI
Genes involved in the mobilization of storage
products that may also function during
other developmental stage. -- Class V and VI
genes would be expressed from the onset of
senescence until the death of the leaf.
68
The function of the protein products of SAGs
based on sequence homology

• I. Genes involved in protein degradation.
• Ex Cysteine protease, Aspartic protease,
  polyubiquitin.
• II. Genes involved in nucleic acid breakdown.
• Ex RNase, uricase, xanthine oxidase.
• III. Genes involved in lipid remobilization.
• Ex malate synthase, Isocitrate lyase, PEP
  carboxylase etc.
• IV. Genes involved in chlorophyll breakdown.
• None.
• V. Genes involved in nitrogen remobilization.
• Ex Glutamine synthetase, Asparagine synthetase.
• VI. Genes with unknown function.

69
(No Transcript)
70

• V. Deciphering he complicated network of plant
  senescence

SENESCENCE -ASSOCIATED (SAG) gene STAY-GREEN
(SGR/SID) gene
Annu. Rev. Plant Biol. 2007. 5811536
71
(No Transcript)
72
Genetic Analysis of Leaf Senescence

• The approach was to identify and characterize
  genes that show enhanced or
• reduced expression during leaf senescence.
• Buchanan-Wollaston et al. (2005). Comparative
  transcriptome analysis reveals significant
  differences in gene expression and signalling
  pathways between developmental and
  dark/starvation-induced senescence in
  Arabidopsis. Plant Journal. 42567 to 585.
• Lim et al. (2007) Leaf Senescence. Annual Review
  of Plant Biology. 58 115 to 136.
• van der Graaff et al. (2006). Transcription
  analysis of Arabidopsis membrane transporters and
  hormone pathways during developmental and induced
  leaf senescence. Plant Physiolgy. 141 776 to 92.
  

73
The utilization of promoter from SAG related genes
74
Molecular Approaches toUnderstanding Leaf
Senescence

• The genetic approach involves isolation and
  characterization of
• mutants that show altered senescence phenotypes.
  So far, most of
• the genetic screening was focused on identifying
  delayed
• senescence mutants from T-DNA or a chemical
  mutant pool, which
• allowed identificationof various important
  positive elements of
• senescence. Early-senescence mutants screened
  from T-DNA or
• chemical mutant pools would enable identification
  of negative factors
• involved in the leaf senescence process .
  However, this approach
• should be taken with the caution that mutations
  with apparent early-
• senescence symptoms may not be directly
  associated with control
• of senescence because mutations in many
  homeostatic or
• housekeeping genes could also give apparent
  early-senescence
• symptoms.

75
Activation tagging of senescence regulator
76
Plant Physiology, June 2001, Vol. 126, pp.
707716
147 out of 1,300 lines displayed senescence-associ
ated GUS expression in leaves. This frequency
(11.3)
77
(No Transcript)
78
(No Transcript)
79
(No Transcript)
80
(No Transcript)
81
Sel101 acyl hydrolase
82
(No Transcript)
83
VI. Different types of programmed cell death in
plants

• 1. Formation of trachery element (TE) in plants
  (Xylogenesis).
• Zinnia mesophyll cells as a model system
• 2. GA and ABA regulates cell death in cereal
  aleurone .
• 3. The arenchyma formation in roots of plants in
  response to
• flooding.

84
(No Transcript)
85
(No Transcript)
86
(No Transcript)
87
(No Transcript)
88
(No Transcript)
89
(No Transcript)
90
(No Transcript)
91
Thanks for everyone of you to stick together
with me for over eight weeks. I think we already
fight for a beautiful war and have a pleasant
memory for this class. Bless you!