Life cycle of Mrachantia plant belonging to Hepaticopsida .ppt

Presentation on life cycle of Marchantia including external morphology, internal structure and reproductin

1. LIFE CYCLE OF MARCHANTIA
DR. AVINASH K. ANEY
M.Sc., M. Phil., Ph.D. SET
Professor and 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

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.

8. REPRODUCTION IN MARCHANTIA
Death of posterior part
Fragmentation
Adventitious branches
Tubers
Gemmae
Spores
Antheridium
Archegonium

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

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 antheridium:
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 perichaetium 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

21. Go Out and Thank a Tree!