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Embryology (発生学)






Mount Usu / Sarobetsu post-mined peatland
From left: Crater basin in 1986 and 2006. Cottongrass / Daylily

Developmental biology

animal
plant

索引

Animal developmental biology (動物発生学)


Gametogenesis (配偶子形成)


Testis and sperm (精巣・精子)

Sperm or spermatozoon (pl. –a) (精子)
The morphology is different at species level. Sperms, mostly consisting of nucleus, contain least nutrients but have high mobility.
sperm
Fig. 32. Diagram of primitive metazoan spermatozoon (Franzen 1956). A: acrosome, H: head piece, M: mitochondrial body, PP: principal piece, MP: middle piece, T: tail section, EP: end piece, C: centriole, N: nucleus. [Sperms of Gymnosperms: Ginkgo biloba and Cycas revoluta]

Egg ()

Organization of egg cytoplams (卵細胞質)

egg
Fig. 63. Redistribution of cytoplasmic inclusions in the egg of Cynthia partita following centrifugation. a, Egg immediately after centrifugation; b, centrifuged egg 22 hours later (the yellow granules, shown black, have taken up a subequational position on one side of the egg). 1st m, Spindle of first meiotic division. (Conklin 1931)

egg
Fig. 1. The four stages of egg maturation at which fertilization occurs in the animal kingdom. (Dalcq 1952)
Lampbrush chromosome (ランプブラシ染色体)

egg
Fig. 3.2. Part of a chromosome from a growing egg cell (oocyte) in the ovary of a salamander showing some of the variety of different kinds of “lampbrush loops” that are formed along the chromosome.


Table. Chemical composition of the jelly coat of echinoderm and amphibian eggs (% dry weight). +, qualitative estimation only; ?, to be controlled; G, glucose; Gl, galactose; M, mannose; F, fucose; X, xylose; Fr, fructose; Ga, glucosamine; Gla, galactosamine; Tot.N., total nitrogen.
SpeciesGGLMFXFrGaGlaTotal NSO4
Arbacia lixula++++
Echinus esculentus+
Paracentrotus lividus4.63.824.30.84.720.9
Strongylocentrotus droebachiensis++25.0
S. purpuratus255.723
Sphaerechinus grarrularis+++
Heliocidaris crassispina+
Echinarachnius parma+
Hemicentrotus pulcherrimus+
Pseudocentrotus depressus+
Echinocardium cordatum32.74.120.5
Brissopsis lyrifera8.1
---
Rana temporaria?12.73.57.1?8.99.58.1
R. esculenta+++?9.3
R. japonica28.0?14.08.8
R. clamitans???++
Discoglossus pictus+++1.716.510.0
Bufo bufo++10.420-407.6
B. vulgaris formosus30.0?20.08.4
Axolotl+++8.3
Triturus cristatus12.21.36.220.310.0

Fertilization (受精)


Theories on fertilization

1. Fertilizin theory (Lillie FR) - negative
2. Lysin corrective factor theory (Loeb)
The issues on Loeb theory: conjunction of sperm and egg (Epel)
Exp. in jelly of sea urchin
sperm → Ca++ permeability (capacitation) → [Ca++ influx] → intracellular Ca++ level, acrosome reaction
→ acrosome

acrosin → dissolution of envelope
lindin → attachment → membrane fusion

→ [Na influx* (phisiological change) ↔ H efflux**]

└* fertilization potential (fast block against polyspermy)
└* intracellular Ca++ level → (a) (b)
└** alkalization of cytoplasm

└ actin polymerization → displacement of cytoplasmic
____________________ constitutions
└ activation of various enzymes
__(ca pH 7.2 = optimum pH for various enzymes)
mRNA is unmasked by this mechanisms (unmasking)

Ex. DNA polymerase → chromosome formation

(a) → cortical vesicle (exocytosis)

└ veteline delaminase → fertilization membran
_____________________(block against polyspermy)
└ sperm receptor hydrolase
_______(attacks binder and slows block against polyspermy)

(b) → oxidation of unsaaturated fatty acid (Ca-activated enzyme)

→ O2 uptake

Table. O2-consumption of unfertilized and fertilized eggs
Species                  Stage of mat.    (O2 uptake of 
                         division         fertilized egg)/
                         at the time of   (O2 uptake of
                         fertili1ization  unfertilized egg)

Nereis succinea                                    1.3
N. limbata               Germinal vesicle          1.35
Mactra laterialis                                  1.8
Urechis caupo                                      1.2
Cumingia tellinoides                               0.45
Chaetopterus variopedatun                          0.53
Marthasteriaa glacialis                            1.0
Saxostrea commercialis   Metaphase of 1st mat.     1.0
Sabellaria alveolata     Division                  1.1
Asterias glacialis                                 1.0
Ciona intestinalis                                 1.5
Phallusia mamillata                                2.0
Rana platyrrhina                                   1.0
Bufo bufo                Metaphase of 2nd mat.     1.0
Fundulus heteroclitus    Division                  1.0
Oryzias latipes                                    1.0
Fucus vesiculosus                                  1.9
Strongylocentrotua purpuratue                      3.7
Psammechinus miliaris                              3.6
Paracentrotus lividus                              4.7
Arbacia punculata                                  4.5
Dendraster excentricus                             3.0

Table. Fertilizability of Asterias eggs at various pH values
               HCl                            NaOH
Concentration   N/   N/   N/   N/  N/ Normal   N/    N/    N/   N/  N/
in sea water   500 1000 2000 4000 104 sea     104  4000  2000 1000 500
                                      water
Cleaved egg %   0   2.5  8   22.5 45    53     84  92.5  88.5   89   0

Cleavage (卵割)


cleavage
Fig. 60. Displacement of organ rudiments in an embryo of Cynthia partita as a result of centrifugation of the egg. n, neural system; p, eyp pigment; ch, autochord; ect, ectoderm; ms, muscle cells. (Conklin 1931)

Table. Cleavage of frog eggs by the injection of tissue (testis) extract and of various fractions of the same obtained by centrifugation.

Preparation________Eggs reaching blastula stage (%)
Whole tissue extract__________94
Large granules______________35.2
Medium and small granules____19.5
Supernatant_________________0
Phosphate buffer_____________0.3
Pricked "dry"________________ 0

Table. Nucleic acid content in nuclei during gametogenesis and cleavage in Chaetopterus
    Stage                 Amount of DNA    Condition of nucleus

    1st polar body          127 ±  3              2n
    Sperinatozoid            61 ±  1              1n
    Cleavage, interphase    210 ±  9              2n-4n
    Cleavage, prophase      263 ± 10              4n
    Cleavage, telophase     124 ±  3              2n

Asymmetric property (非対称性)

1928 Spearman

Spearman
Fig. 13. "Retarded nucleation" in Triton. Zygote nucleus pushed to one side by the constriction of the egg. (a) first cleavage. In the nucleated half; (b) further cleavages In this part, the other half Is still imcleaved; (c) passage of one nucleus from the nucleated into the non-nucleated half, beginning of development In the latter; (d) the two embryo. that developed from the constricted (収縮された, 窄まった) egg; the one produced by the half In whIch nucleation was retarded is considerably younger, but normally built. (Spemann and Tannhauser 1938)

1953 Briggs & King: Rana pipiens

Organogenesis (器官形成)


Development of gonad (生殖腺発達)

1. Origin of primordial germ cell (gamete) (始原生殖細胞の起源)
organogenesis
Fig. Diagrams showing the displacement of the germinal cytoplasm during the early development of Bufo regularis.
2. sex differentiation (性分化)

Pre-embryo (初期胚)

= early embryo or nascent embryo
blastula
Fig. Diagrammatic comparison of blastulae (胞胚) of an echinoderm (a), a frog (b), a bony fish (c) and a bird (d).

Gastrulation process (嚢胚形成過程)


gastrula
Fig. A, B, development of an embryo with animal pole material graft placed in the grey crescent. A, during gastrulation; B, after neurulation. nt, neural tissue, ntt, non-neural tissue, C, D, E, development of an embryo with grey crescent graft at ventral margin. In C embryo shows two neural plates and dorsal lips, one induced, the other normal, D, E show two extreme types of embryo which are produced by these grafts, after neurulation.
sea urchin
Fig. Segmentation and gastrulation in sea urchin. a) fertilized egg, b) 2 blastomere stage, c) 4 blastomere stage, d) 8 blastomere stage, e) 32 blastomere stage, f) blastula (appearance from above), g) blastula (longitudinal section), h) arising of first mesenchyme cells, i) gastrula occurrence. Bld-blastoderm: 1.a.g. first abdominal gap, 1.m.c. first mesenchyme cells.
sea urchin
Table. Chemical composition of sea urchin embryo (% wet weight)
    Substance         Unfertilized   Blastula   Pluteus
                           egg       (12 hrs)

    Water                  77.3       77.3        78.8
    Dry substances         22.7       22.7        21.2
    Protein nitrogen       10.7       10.2         9.7
    Total carbohydrates     5.43       5.46        3.4
    Glycogen                5.13       4.8        traces
    Fat                     4.82       4.43        3.69
    Ash                     0.34       2.07        3.56

Table. Chemical composition of the egg and embryo of a frog (mg)
    Substance                          Egg  Hatched tadpole

    Total nitrogen                      162       159
    Extractable nitrogen                 40        42.8
        (N of active protoplasm)
    Nonprotein nitrogen                   4         5.0
        (in nucleic acid?)
    Total carbohydrates                 104        58
    Glycogen                             73.2      31

Table. Chemical composition of the eggs and later stages of development in three species of dog fish (g)
    Species                   Egg   Young

    Scyllium canicula (oviparous)
        Total weight          1.3    2.7
        Organic substances    0.61   0.48
        Water                 0.68   2.15
    Mustellus vulgaris (ovoviviparous)
        Total weight          3.9    60.6
        Organic substances    1.9     8.9
        Water                 1.9    49.8
    Mustellus laevis (viviparous)
        Total weight          5.5   189.0
        Organic substances    2.8    32.0
        Water                 2.6   152.0

mammal (哺乳類)

Neurula (neurula stage, 神経胚)


ectoderm: epidermis, neural tissues, neural crest cell
mesoderm: 体節somite → muscle, nephorotome → excretory system, lateral plate → somatic layer, parietal l.
extraembryonic structures (胚体外膜)

yolk sac (卵黄嚢), amnion (amniotic sac, 羊膜), chorion (漿膜), allantois (尿膜)

archenteron (primitive gut, 原腸)
enteric (gut tract, 腸管)
neurula
neurula
Fig. 78. Gastrulation of Amphioxus. A series of consecutive stages (median sections). (Conklin 1932)

Neural induction (神経組織誘導)

gastrula
Fig. Diagrammatic illustration of the morphogenetic movements. (a) of normal gastrulation, and (b) of exogastrulation. c, main differentiations in an exogastrulated embryo. (Holtfreter 1933)
gastrula
gastrula
gastrula

Developmental fate (発生運命)


1920-30 Spemann: completed the fate map a few years before

discovered organizer, by using hair loop, glass needle, pipette, etc.

Organizer (形成体)
= dorsal lip
1) neural induction (神経誘導) – mesoderm, endoderm
2) organization center of embryo

neural induction
embryonic induction
primary induction
⇒ not only dorsal lip but also the others can be organizer

Analysis for nature of induction (誘導特性解析)

Technical
grafting in vivo (A, B) → tissue (organ) culture system in vitro (C, D)
fate
Figure 165. Four methods of exposing gastrula ectoderm to induction (diagrammatic). A, Transplantation of part of dorsal lip (stippled) into the ventral marginal zone, where it invaginates and forms a secondary archenteron. B, Transplantation of part of dorsal lip (stippled) into the blastocoele through a slit at the animal pole. Graft is eventually pressed against the ventral ectoderm. C, "Sandwich experiment": inductor (such as a centrifuged tissue homogenate) placed between two pieces of presumptive gastrula ventral ectoderm. D, Cultivation of a piece of presumptive ventral ectoderm of a gastrula in a watch glass filled with fluid containing inducing substance in solution. The reacting ectoderm is held between two layers of supporting material (silk) to prevent it from curling.
fate
Fig. Cell-transfer experiment

formation of limb (or wing) on vertebrate (脊椎動物における肢(羽)形成)


Renal system (腎臓系)

developed from nephrotome, showing the relationship between ontogeny and phylogeny
renal system
pvc: posterior vena cave, bc: blood corpuscles, md: mesonephric (Wolfflan) duct, ga: gonad anlage, pp: presumed path of primordial germ cells to gonad anlage

gonad (♂/♀) (mesodermal) ┅┅┅ different origin
_________↑ incursion_______
_________primodial germ cells (始原生殖細胞) → sperm or egg
┣ ovary ━━━━━┓
┗ testis ━━━ sperm or egg determined by the surrounding tissues
__⇑ hormones
[testis, mesonephros – urinary duct, Wolffian duct]
[ovary, pronephros – Müllarian duct, oviduct]

Metaphros (kidney, 腎臓)
mesodermal epithelium, mesodermal mesenchyme

renal system vreteric bud - mesencyme - branching - collecting duct
(尿管芽)______┗━━━━━┛
_____________condensation (forming duct)
______________________→ uriniferous tubule
renal system
a) epithelium: singular separation (分離単独) → no differentiation / mesenchyme: singular separation → no differentiation
b) ureter: dependent on metanephic mesenchyme
c) uriniferous tuble [replacement is possible to salivary gland epithelium, spinal cord]: not dedepnent on ureter (ureteric bud)
⇒ the formation of urinary duct is "permissive"
mesenchyme: cell adhesion is weak prior to the formation of ureteric bud

Pattern formation (パターン形成)

1) limb field and limb area
1910 Harrison: Salamander tail bud

a) destroyed 1/2 limb bud → normal limb
b) slit limb bud vertically → duplicated limb
c) combined 2 lim buds in harmonous orientation → normal limb
d) rotated limb field at 180o and transplanted →

AP-axis: neural tube closure stage / DB-axis: tail but stage

Proximal-distal: forming limb (need re-consideration)

2) limb bud – polarity

A-P / D-V, somatic layer mesoderm, epidermis epithelium

3) mesodermal-ectodermal interaction

Synthesis (合成)


synthesis
synthesis
Fig. 86. Changes in the synthesis of various classes of nucleic acids in oogenesis, at fertilization, and during early development in the frog embryo. (Gurdon 1968)
synthesis
synthesis
Fig. Maternal inheritancee and manifestation of the o gene in the axolotl (Briggs & Justus 1968)

Immunological response and immune system (免疫反応と免疫システム)


Table 17. Properties of non-IgM immunoglobulins of lower vertebrates.
Species      Class     Intact   Light Heavy CHO(%)  Desig-  Formula
                                                    nation

Lung fish    Dipnoi    120000   22000 38000 N.D.     IgN    L2υ2
Bullfrog     Amphibian (150000) 22000 53000 2.0      IgG ?  L2γ(?)2
Marine toad  Amphibian 160000   22500 53000 4.2      IgG ?  L2γ(?)2
Xenopus      Amphibian N.D.     22000 53000 N.D.     IgG ?  L2γ(?)2
                                26700 64500
Turtle       Reptile   180000   22500 67500          IgG(Y) L2γ(Y)2
                       120000   22500 38000 0.9      IgN    L2υ2
Sleeply      Reptile   151000   22400 51000 N.D.     IgG ?  L2γ(?)2
lizard
Duck         Avian     178000   22400 68000 5.0      IgG(Y) L2γ(Y)2
                       118000   23000 35000 0.6      IgN    L2υ2
Chicken      Avian     174000   22500 67500 2.2(HEX) IgG(Y) L2γ(Y)2
                       N.D.     N.D.  N.D.  N.D.     IgA    (L2α2)
Echidna      Monotreme 150000   22500 49000 2.0(HEX) IgG    L2γ2
             mammal

Cell-mediated immunity (cellular immunity)

Ab: overlays on cell surface – Ag-receptor

Humoral immune response: plasma cell → Ig circulation
Cellular immune resposne: lymphocytes → Ab

Genetic basis of cellular immune response


                                              Accept   Reject

    1) isograft (= autograft), isogenic          O
    2) allograft                                         O
    3) AA × BB (P)         Transplant P → F1   O
       → AB (F1)           F1 → P                      O*
    4) → AA, AB, BB        F2 → F1             O

*: reject the substances that have not present in itself

Plant developmental biology (植物発生学)


Morphogenesis (形態発生)

____seed germination
________
________formation and growth of stem and root ←
________↓ senescence and abscission_________
________↓ bud dormancy →→→→→→→→→→→
________formation of flower
________↓ senescence and abscission
________fruit set →→→→→→→→ seed formation
_________________________________
________growth and riping of fruit______
____←←←←←←←←←←←←←← seed dormancy
development

Polarity (極性)

young: shoot apical meristem (root as well as stem)
young: root apical meristem

meristem (meristematic tissue) - absent in animals

Plant hormones (植物ホルモン)


Auxin

Gibberellin

Cytokinin

Abscisic acid

Ethylene

Florigen

Changes in RNA metabolism induced by auxin

Table. Requirement of nucleoplasimic factor for enhanced RNA synthesis by IAA (Unit = 3H-UMP incorporated (c.p.m))

Incubation system____________Unit


Complete___________________336
Complete – DNA______________ 56
Complete + IAA______________328
Nucleoplasm only_____________ 72
Nucleoplasm + IAA____________ 68
Complete + nucleoplasm_______412
Complete + nucleoplasm + IAA__727


Table. Simulation of RNA synthesis by IAA and acceptor protein in vivo

Incubation system_β, γ32P-ATP incorporated_3H-UMP incorporated
________________(pmol/mg of enzyme)____(nmol/mg of enzyme)


Complete_______________________60______________6.3
Complete + acceptor protein________35______________4.2
Complete + acceptor protein + IAA__108_____________14.8


Table. Comparison of RNA polymerase activity by incubation of plasma membrane in 0.1 μM 2,4-dichlorophenoxyacetic acid, indoleacetic acid, or 3,5-dichlorophenoxyacetic acid.

________[3H]-UMP incorporated (pmol/30 min/mg protein)


RNA polymearase____________88
+ PM-IAA_________________ 146
+ PM-2,4-D supernatant______138
+ PM-3,5-D supernatant_______96


PM, plasma membrane fraction

Table. Enhancement of RNA polymerase activity by incubation of plasma membranes in 2,4-dichlorophenoxyacetic acid. Numeral = [3H]-UMP incorporated (pmol/30 min/mg protein)

RNA polymerase____________________________________ 72
+ PM suspended in TGMED__________________________ 162
+ Repelleted PM resuspended in TGMED________________116
+ TGMED supernatant after PM repelleted________________74
+ PM suspended in TGMED + 0.1 μM 2, 4-D_____________ 236
+ Repelleted PM resuspended in TGMED + 0.1 μM 2, 4-D___162
+ TGMED suspended after PM repelleted with 0.1 μM 2, 4-D_106
+ TGMED + 0.1 μM 2, 4-D_____________________________84


PM, plasma membrane fraction

Table. Effect of α-amanitin on enhancement of RNA polymerase by auxin-related factor.

RNA polymeraase__________________160
+ α-amanitin*______________________133
+ PM-2,4-D supernatant_____________ 227
+ PM-2,4-D supernatant + α-amanitin*__ 140
RNA polymerase___________________186
+ α-amanitin*______________________146
+ PM-IAA supernatant_______________267
+ PM-IAA supernatant + α-amanitin*___ 140


* α-amanitin acts as the inhibitor of mRNA synthesis. Each assay contained 2 μg of α-amanitin


      PLASMA    CYTOPLASM  NUCLEAR    NUCLEUS
      MEMBRANE             MEMBRANE
Auxin   | |                  | |
-----→ | | ---→ Factor -→ | |--→ Factor + RNA polymerase
        | |                  | |      ↓
        | |                  | |     Modified RNA polymerase
        | |                  | |      ↓
        | |                  | |     Altered genome transcription
A hypothesis in relation to the synthesis of nucleic acids operated by auxin.
alpha;-amylase formation induced by gibberellin
GA
(left) α-amylase as % of total cell free protein synthesis. (right) Rate of α-amylase synthesis in vivo (U per 120 min)
Hormonal control on hormone level
Auxin-induced ethylene production - regulation of ethylene biosynthesis -

RA + RB = RAB ← additive response (R: response, AB: hormones)
RA + RB < RAB ← synergistic response
IAA, ABA, Cytokinin havce complementary functions

Cell cycle (細胞周期)


Differentiation (分化)


1968 Harris H

Ⓧ + ◎ + UV irradiation → differentiation


                             Amoclae    F hoclies

        Dry weight             5-8        2.5-4
        Protein                2-5        1.5-2 ↓
        RNA (mg)               1          0.4
        Total carbohydrate     0.5        0.4 =
        Cellulose              0          0.1
        Mucopolysaccharide     0          0.08
        DNA                   36         30

de novo: Ex. temporal changes in the synthesis patterns of actin (structural protein)

differentiation
Fig. Decrease in dry weight and oxygen consumption

the most of energy during the emergence process is from protei. carbonhyborates are used least
→ expression of genes that are for storage-specific proteins and the RNAs

1972 Firtel RA

3H-DNA → thermal denaturation for single strand → sharing force, ca 400 nucleotides → remnant, return to double strand (= repeated sequence) → hydroxyappite column
3H-labeled single strand = DNA (unique sequence) → probe DNA-RNA hybrid


                          % of genome      Estimated
                          present as RNA   number of genes
                          transcripts      expressed

      Growth                  30.2 (%)           8600
      Aggregation             27.4               7800
      Pseudo-plasmodium       34.2              10000
      Culmination             35.6              11000
      All stage               56.0              11000
      Growth + Culmination    49.0

Growth + (Growth + Culmination) = 65.8: common genes present
2.86 × 107 nucleotide pair → one gene = 103 bp (M.W. = 4300) ⇒ unique gene = 286 × 104

Key enzyme (キーエンザイム)
UDP-galactose (polysaccharide) transferase: spore-specific substances

enzymes related to carbohydrate synthesis (cf. PSV: prespore vacuole) - absent in the stalk

Ex. Blastocladiella emersonii (水生菌), Acetabularia mediterranea

nuclear-cytoplasm interaction after the nuclear transfer

Higher plants (高等植物)
seed: analogy of animal embryo
Ex. α-amylase / β-amylase

de novo: gene = active → m-RNA → protein (α-amylase)

Germination and growth (発芽と成長)


embryo: gibberellin synthesis after immersion → active α-amylase synthesis → auxin → differentiation

Seed formation (種子形成)


Double fertilization and division pattern

double fertilization
Fig. Life cycle of Angiospermae (Engler’s Syllabus 1964)
embryo
Fig. Embryo development in Daucus carota. Longitudinal sections. The lower end of embryo in each drawing is the end directed toward micropyle. A-C, stages in development of linear four-celled embryo. D, E, two common variations in eight-celled embryos: difference in division of cell a of the four-celled embryo. F-I, older embryos varying in cell arrangement. J, embryo differentiated into main body and suspensor. Initial organization of tissue regions is present in J. Relation of parts of certain embryos to cells of the four-celled embryo (C) is indicated by the letters a-d. (Borthwick 1931).
double fertilization
Fig. Embryo development in Lactuca sativa (lettuce). Longitudinal sections. Lower end of embryo in each drawing is the end directed toward micropyle. A, zygote in division. B-G, embryos in successive stages of development, showing establishment of several horizontal tiers of cells. In G, cell h later gives rise to all of the suspensor cells, and the tiers above h develop into the main body of embryo. H-M, further development stages.

Dormancy (休眠)


Cell differentiation and growth (細胞の分化と成長)


Shoot apex (茎頂)

Relationships between stem and root (茎と根の関係)
1950 Skoog: Tobacco pith

IAA 0.002 ppm → root
Adenine 40 ppm → stem (leaf)
IAA 0.005 ppm + Adenine 40 ppm → stem, leaf, root

1957 Skoog & Miller: Tobacco pith  Callus

_____________Callus___Roots___Leaves
IAA (mg/l)______3______3________0.03
Kinetin (mg/l)___0.2_____0.02_____ 1

1958 Steward (USA): liquid medium – free cell

1) embryoid (胚様体)
2) origin = unicell (plant): (need to obtain the evidence)

1965 Vasil & Hildebrandt

tobacco pith cells → culture single cell → can form both bud and root

1965 Chen & Gaglston: Pelargonium pith collecting from pith → callus

medium: auxin, kinetin + agar → to liquid: differentiate root, stem and leaf
in general, the differentiation occurs under auxin-free condition ← substances for growth regulation

1970 Backs-Hüsemann & Reinert: unicell → embryoid
1971 Nagata & Takebe (長田・建部): Tobacco mesophyll protoplast

→ mature plant/embryoid → callus mass

Defoliation and shedding (落葉・落花・落果)


Defoliation (落葉)

C2H4: promoting cellulase in the abscission layer (or zone)

Lamina senescence____Abscission layer(zone)
___________________
IAA production →→→→ Stimulate senescence
____________________
_________C2H4(exo) ⇔ C2H4 production
____________________
____________________Increase cellulase
____________________
____________________Cell separation

Defoliation process (落葉過程)

cell differentiation plant hormones
_____________ _______________specific gene activation
functional specification specific enzyme
____________________
specific structure__specific protein ← specific mRNAs _______________ or polypeptide___
______________________________specific transcription
Fig. Conceptual framework for predicted cell differentiation processes

Flower shedding (落花)

Fruit shedding (落果)

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