Structure & Life Cycle of Marchantiacms.gcg11.ac.in/attachments/article/115/Marchantia.pdfStructure...
Transcript of Structure & Life Cycle of Marchantiacms.gcg11.ac.in/attachments/article/115/Marchantia.pdfStructure...
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Structure & Life Cycle
of Marchantia
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Marchantia
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General Characters
External surface of thallus (DorsalDorsalDorsalDorsal viewviewviewview)
�Shows prominent midrib at the apex of whichgrowing point is situated
�Branch Dichotomously at the Apex.
�Thalli also show cup like structure (Gemma�Thalli also show cup like structure (GemmaCups)
�Gemma cup encloses a number of gemmaemeant for asexual reproduction.
�Sex organs are borne on special uprightbranches attached to dorsal surface nearapical notch.
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Lower (Ventral) surfacesLower (Ventral) surfacesLower (Ventral) surfacesLower (Ventral) surfaces Upper (Dorsal) surfacesUpper (Dorsal) surfacesUpper (Dorsal) surfacesUpper (Dorsal) surfaces
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General CharactersExternal surface of thallus (VentralVentralVentralVentral viewviewviewview)
�Shows median longitudinal groove.
�Rhizoids and scales are present.
�Rhizoids may be smooth walled ortuberculatedtuberculated
�Scales arranged in 2-4 rows on each side ofmid rib.
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General Characters
Internal structure of thallus
�Epidermal regions: Dorsal and Ventral
epidermis.
�Photosynthetic (Assimilatory) Zone: Layers of
chlorenchyma below the dorsal epidermis. Thechlorenchyma below the dorsal epidermis. The
photosynthetic cells are slightly columnar and
there is a lot of air space between the cells
(Aerenchyma).
�Storage Zone: In ventral region, subtends the
chlorenchyma.
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Asexual reproduction� Fragmentation: Occurs by
death and decay of posteriorportion of thallus.portion of thallus.
� Adventitious branches:Develop on any part ofthallus, separate and growinto new plant.
� By Gemmae: Gemmae areproduced inside cup shapedgemma cups. These cups areproduced on dorsal surfaceof thallus close to growingapex, along midrib.
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Marchantia's Gemmae Cup Cross Section
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Sexual reproduction
�Oogamous type
�All species are dioecious.
�Sex organs: antheridia (male) andarchegonia (female)
�Antheridia borne on antheridiophore�Antheridia borne on antheridiophore
�Archegonia borne on archegoniophore.
�Sex organs appear once a year in April-May.
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Sexual reproductionAntheridia
�Antheridiophore is differentiated into Stalk and Disc.
�Disc is 8-lobed, each representing a single branchof thallus.of thallus.
�Disc is thick in middle and thin towards periphery.
� It resembles thallus and divided into air chambersalternating with antheridial chambers.
�Antheridia are borne inside antheridial chambers.
�They are arranged in 8-radiating rows on dorsal(upper) surface of disc, reach row representing asingle branch of thallus.
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Antheridial Disc
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Sexual reproduction
Antheridia�Mature Antheridium isdifferentiated into Stalkand Body.
�Body has a single layeredjacket, encloses largenumber of androcyteswhich metamorphore intowhich metamorphore intoanthrozoids.
�Antheridia dehisce inpresence of water.
�Sterile jacket imbibeswater and antherozoidsooze out in mass and swimin water film.
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�Also called Carpocephallum.
� It is differentiated into Stalk and Disc.
�Stalk is short and elongates after fertilization.
Sexual Reproduction
Archegonia
�Stalk is short and elongates after fertilization.
�Disc is 8-lobed directed away from centre.
�Archegonia develops on upper surface of discin acropetal (youngest archegonium is neargrowing point of lobe and oldest in the centreof disc) succession in 8-rows.
�Each row represent single lobe of thallus andbears 12-18 archegonia.
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Sexual reproductionArchegonia�After fertilization, stalk elongates, centralportion of disc buldges out pushing archegoniaat periphery.
� It results in complete hanging (downward) ofarchegonia.
� It results in complete hanging (downward) ofarchegonia.
�It shifts youngest archegonia to reach nearstalk and oldest and fertilized towardsperiphery.
�Intercalary growth occurs between fertile lobeswhich results in formation of radially elongatedgreen outgrowths called RAYS.
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Sexual reproduction
Archegonia� Internal structure of disc shows photosynthetic zoneconsists of air chambers.
� The archegonia are arranged in 8-radiating rows on lowersurface of disc.
� Archegonia are inverted and hand downward from tissue ofdisc.disc.
� Each archegonia has an extra sheath called PERIGYNIUM.
� Each group of archegonia are enclosed in 2-lippedinvolucres called PERICHAETIUM.
� Mature archegonium is flask shaped consists of stalk,venter and long neck.
� In mature archegonium, neck canala cells and venter canalcells disintigrate and become mucilagenous whichabsorbs water and put pressure so as to get separated.
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Fertilization
�Occurs in presence of water.
�Male and female thalli of Marchantia grow in closecompact masses.
�The antherozoids (biflagellated)swim in cavity ofdisc of antheridiophores.disc of antheridiophores.
�The antherozoids fall on disc of archegoniophoreand flows down to its neck and fuses with egg.
�Haploid nucleus of antherozoids fuses with haploidnucleus of egg and forms zygote.
�The zygote is the first cell of sporophytic generation.
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The Sporophyte
�Each sporophyte is divided into FOOT, SETA andCAPSULE
�The archegonia are ranged in 8-radiating rows onlower surface of disc.
�Archegonia are inverted and hand downward from�Archegonia are inverted and hand downward fromtissue of disc.
�Each archegonia has an extra sheath calledPERIGYNIUM.
�Each group of archegonia are enclosed in 2-lippedinvolucres called PERICHAETIUM.
�Mature archegonium is flask shaped consists ofstalk, venter and long neck.
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The Sporophyte
• FootFootFootFoot, which both anchors the sporophyte in
place and receives nutrients from its
"mother" plant,
• Setaetaetaeta (stalk), which lies between the other
two regions and connects them.two regions and connects them.
• CapsuleCapsuleCapsuleCapsule, inside which the spores are
produced for dispersing to new locations,
• At maturity, the sporophyte the seta
elongates, pushing its way out of the
archegonium and rupturing it.
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The Sporophyte
• Foot remains anchored within the parent plant,
the capsule is forced out by the seta and is
extended away from the plant.
• Within the capsule, cells divide to produce
both elater cells and spore-producing cells.both elater cells and spore-producing cells.
• The elaters are spring-like, and push open the
capsule wall, capsule bursts and scatter
themselves.
• The spore-producing cells undergo meiosis to
form haploid spores to disperse, upon which
point the life cycle start again.
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Old Archegoniophores with
attached sporophytes
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Marchantia Sporophyte
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Marchantia Sporophyte
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