1. LIFE CYCLE OF MARCHANTIA
DR. AVINASH K. ANEY
M.Sc., M. Phil., Ph.D. SET
Head
Department of Botany,
Science College, Pauni, Dist. Bhandara
2. Occurrence and distribution:
Cosmopolitan in habitat
Genus comprising 65 species. M. ploymorpha is widely distributed
11 species reported from India (Chopra, 1943)
Mostly confined to Himalayas
6 species reported from Himalayas (Udar, 1970): M. palmata, M. nepalensis, M.
polymorpha, M. simalana and M. indica
Commonly found on moist soil on rocks in shady places in Kashmir, Kumaon, Punjab,
Leh, Laddakh, Kolkata, Assam, etc.
Classification and systematic position:
Division: Bryophyta
Class: Hepaticopsida
Order: Marchantiales
Family: Marchantiaceae
Genus: Marchantia
3. External features/External morphology:
Plant body is thalloid gametophyte, prostrate, (upto 2 to 10 cm)
Thallus dorsiventrally differentiated, lobed and dichotomously branched
Dorsal surface: Dark green in colour and smooth
Ventral surface: Faint green in colour and rough in appearance
Apex of each branch is with apical notch in which growing point is situated
Prominent dark coloured midrib present on dorsal surface
Cup-like structure present exactly on midrib towards apical region (Gemma cups)
Gemma cups contains numerous, green, flat, stalked vegetative bodies called gemmae
Ventral surface is with pinkish, multicellular scales protecting growing points
Scale divided by narrow constriction into two parts, the body and appendage
Presence of both types of rhizoids: Smooth walled and tuberculated
Rhizoids absorb water and minerals from soil and anchor the thallus with substratum
4.
5. Internal structure of the thallus: (V.S. of thallus)
Thallus shows elaboration of tissue
Many cells in thickness.
The cells are arranged in three distinct regions
1. Epidermal region:
Thallus is covered by well-defined upper and lower epidermis.
Upper epidermis also called dorsal epidermis forms the surface layer over the
photosynthetic region.
Consists of single layer of thin-walled cells.
Epidermal cells contains few chloroplasts. It is protective in function and checks the
transpiration.
Dorsal epidermis is not continuous and is interrupted by the stomata like structures
called air pores. Air pore is surrounded by four tiers of four cells each. Presence of air
pore facilitates gaseous exchange.
Lower surface is covered by single layered thick lower or ventral epidermis. It is
continuous and bears both the types of rhizoids and scales
Lower epidermis protects the thallus from lower side and provide surface for the
formation of rhizoids and scales
6. 2. Photosynthetic region
Below the upper epidermis, large sized air chambers are present.
Arranged in single horizontal row.
Chambers are bounded by one cell thick partition wall, which are three to four cells in
height.
Each chamber open outside by the barrel-shaped air pore.
The chamber contains short, simple or branched filaments of green cells called as
assimilatory or photosynthetic filaments.
7. The cells of these filaments contains numerous chloroplasts.
This region is the site of photosynthesis and hence also called assimilatory or
photosynthetic region.
3. Storage region
Present below the photosynthetic region towards ventral surface.
It is thick in the center and reduced to 3-4 layers of cells towards margins.
Consists of uniform tissue made up of relatively large, colourless, thin-walled
polygonal parenchymatous cells. The cells are without chloroplasts and contains
starch and protein grains.
This region is covered from ventral surface by single layered lower or ventral
epidermis.
9. 1. Vegetative reproduction:
Takes place by following ways
A. Fragmentation:
Occasionally, older mother plant is broken into several fragments.
Separted fragments with growing point develop into young thallus of Marchantia.
B. By death and decay of posterior part of thallus:
The older posterior part of the thallus disintegrates due to ageing.
When this decay of cells reaches dichotomy, the lobes become separated.
Each detached lobe with growing point can develop into new plant of Marchantia.
C. Formation of adventitious branches:
In some species, small adventitious branches develop from margin of thallus
These branches detached from the thallus and may develop into new thallus of
Marchantia.
D. Formation of tubers:
Spherical tubers develops on the marginal region
Detached from the mother plant
Each tuber develop into young plant of Marchantia
10.
11. E. By gemmae:
Most common method of reproduction in Marchantia
Gemmae: Special vegetative reproductive structure produced in gemma cups
Structure of mature gemma:
12. Mature gemma is attached by a single celled stalk attached to the base of gemma cup
Disciform and few celled thick in center and thin in margin
Gemma is dump bell like
It has two depressions or notches on the lateral margins opposite to each other
Growing point is present in the notches
All the cells contains chloroplast
Some larger cells are colourless containing oil called oil cells, which develops into
rhizoidal cells
Rhizoids arise from these cells
A. Germination of gemma:
Detached gemma falls on suitable soil and germinate
Rhizoids comes out from the rhizoidal cells and enter the soil
Growing point in the notches activate and develops into young gametophyte
Two young gametophyte develops from single gemma
13. B. Asexual reproduction:
Takes place by spores produced in sporophyte
C. Sexual reproduction:
Sex organs are antheridia and archegonia
Develops on the special erect stalked structure called antheridiophore and archegoniophore
Structure of anthrediophore:
E
Each
Modified branch bearing antheridia
Arise from apical notch of the matured lobe of male thallus
Differentiated into two to three cm long stalk, and a flattened,
eight lobed disc at apical end.
The antheridial disc is somewhat convex
Internally differentiated into elongated stalk and flattened disc
at the apex
Stalk is elongated and multi-layered
Rhizoids arise from the lower portion
Antheridial disc is convex and consist of antheridia
Upper portion of the disc is photosynthetic with alternate air
chambers and flask-shaped cavities, called anthredial cavity
Upper epidermis is interrupted by barrel shaped air pores
Air chambers contains photosynthetic filaments and opens
outside by air pores
Each anthredial cavity contains single, stalked anthredium
Anthredial cavity opens outside by an opening called ostiole
14. Structure of mature anthreduim:
Mature antheridium is oval shaped structure
Consist of short stalk and rounded body
Body of antheridium is surrounded by single layered jacket
It contains densely crowded large number of androcyte mother cells
Antherozoid:
Structure of archegoniophore:
E
Each
Androgonial cells in the antheridium divides to form androcyte mother cells
Each androcuye mother cell divides to form androcytes
Androcyte metamorphoses into male gamete, antherozoid
Each antherozoid is elongated, rod-like, uninucleate and biflagellate structure
Two equal length flagella arise from anterior narrow end
Posterior end, somewhat swollen containing male nuclei
The antherozoids move by swimming on the film of water with the help of flagella
Antherozoids are chemotactic and motile
Stalked and elongated structure
Modified branch producing archegonia
Differentiated into elongated stalk and forked disc at the apex
Bears archegonia attached to the lower surface of the disc
15. Internally, it consists of elongated stalk and
archegonial disc
Stalk is multicellular and 4-6 cm long
Archegonial disc is convex and forked
Disc is having large air chambers containing
photosynthetic lamellae
Covered by interrupted upper epidermis
Each air chamber opens outside by air pores
Archegonia develops on the upper surface of
the disc
Fertilization takes place at this stage
After fertilization, marginal portion of the disc becomes inverted and the archegonia now become
hanging on the lower surface
There are 12-15 archegonia present per archegoniophore
Older archegonia situated towards periphery and the younger close to the stalk
After fertilization, single layered plate of tissue develops on either side of group of archegonia
It is called perichetium that protects the group of archegonia
Structure of mature archegonium:
Mature archegonium is flask shaped structure, attached to the lobe by small stalk
Consist of elongated neck and a broader venter
Neck is covered by single layer of cells called wall or the jacket of archegonium
16. Axial row of four or more neck canal cells (NCC) present in the neck
Venter is somewhat swollen and surrounded by a single layered jacket
Venter contains large basal egg cell (n) and upper venter canal cell (VCC)
Egg is also called as oosphere
At the tip of neck, four cells are compactly arranged, called cap/lid or cover cells
These cells open to form minute opening for the entry of spermatozoids
Fertilization:
Act of union of haploid male gametes (n) with haploid female gamete (n) is called
fertilization
Water is very essential for the act of fertilization
Pre-fertilization changes:
Matured antheridia opens due to water
The biflagellate antherozoids liberated in masses and swim on the film of water to reach
archegonia
Chemotactic and free swimming antherozoids reaches the mouth of archegonia
All NCCs and VCC disintegrates to form mucilage substance containing malic acid, proteins
inorganic salts of potassium.
Mucilage substance absorb the moisture and swells. It exerts a pressure on the walls of
archegonium resulting in the separation of cover cells forming the opening for the entry of
spermatozoids
Many antherozoids enter the archegonium, travel through neck and.
However, only one of it discharge the nucleus that fuses with the egg nucleus to form zygote (2n)
h
17. Post-fertilization changes:
Fertilization takes place inside archegonial venter
Fertilized egg (2n) begins to enlarge, secrete a cellulose wall around and develops into
zygote
Zygote enlarges in its size and fills the entire venter cavity
Zygote divides first by transverse wall producing two celled embryo
Embryo divides and redivides to produce spore producing structure called
Sporogonium
Many changes taken place in archegoniophore after fertilization
Stalk of the archegoniophore begins to elongate and ultimately becomes 3-4 cm long
Cells in the venter wall also divides to form two or more celled thick calyptra
Calyptra covers the sporophyte and protect the developing sporophyte
Some of the cells at the base of venter also divides repeatedly giving rise to a one celled
thick collar-like structurer called perigynium, which acts as a protective structure.
It enclose the young sporogonium
Finally, the matured sporogonium is covered by three protective layers: perichaetium,
calyptra and perigynium
18. Sporophyte:
Fertilization takes place inside archegonial venter
Differentiated into three regions: the foot, seta and capsule
Foot is bulbous, present towards the base of fertilized archegonium
Absorptive structure: absorbs nutrition and water from the
gametophyte
Middle portion is seta. It is somewhat elongated and connects the
foot and capsule
Seta helps is pushing the capsule out of protective coverings.
Capsule is the only fertile portion, situated at the apex
Somewhat oval in shape
Covered by single layered jacket or wall of capsule
Capsule cavity accommodates numerous spores and elaters
Elaters are sterile and hygroscopic, spindle-like structure
Elaters shows spiral thickenings
Contraction and relaxation of elaters helps in dehiscence of
spores
Spores are initially present in tetrad (group of four spores)
Sporogonium is covered by calyptra, perigynium and
perichaetium
19. Dehiscence and dispersal of spores:
On maturation, capsule comes out of three layers by elongation of seta
It hangs downward from the lower side of archegonial disc
Wall of mature capsule ruptures forming longitudinal slits
The elaters are hygroscopic
In dry condition, they lose water and get twisted.
The coiling reopen during moist condition
The action of elaters helps in release of spores from the ruptured capsule
The released spores are dispersed by wind
Structure of spores:
Spores are small and spherical, range from 12 µ to 30 µ in diameter
Centrally placed haploid nucleus and small amount of granular cytoplasm
Covered by spore wall, differentiated into outer thick, inelastic, rough,
sculptured layer called exospore or exine and inner thin, elastic and
smooth called endospore or intine
The spores start germination immediately during
favourable condition
Absorb water and increase in size
Intine protrudes out in the form of germ tube through germ
pore
Nucleus divides to form two celled structure, which further divides to form long irregular filament
Rhizoids comes out from lower surface and enter the soil
Finally, it develops into young gametophyte of Marchantia
20. Life cycle and alternation of generation:
Life cycle is heteromorphic and haplodiploidy type
Consist of two phases i.e. gametophytic and sporophytic
Gametophytic phase is haploid, first, dominant and independent
Sporophytic phase is diploid, second, conspicuous and dependent on the gametophyte
Two important events takes place in life cycle i.e. fertilization and meiosis
Fertilization results in diplodization (2n)
Meiosis results in haplodization (n)
Two phases comes in alternate manner with one another, hence called alternation of generation