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1. Details of Module and its Structure
Module Detail
Subject Name Botany
Paper Name Systematic I (Bryophytes)
Module Name/Title Diversity in Sporophyte
Module Id
Pre-requisites
Objectives
Keywords Foot, Seta, Capsule, Spore, Elater
2. 2. Development Team
Role Name Affiliation
National Coordinator
Subject Coordinator
Paper Coordinator Dr A. K. Asthana National Botanical Research Institute, Lucknow Content Writer/Author (CW) Prof. GeetaAsthana Botany Department Lucknow University, Lucknow Content Reviewer (CR) Language Editor (LE)
Systematic I (Bryophytes) Botany Diversity in Sporophyte
Structure of Module/Syllabus of a module (Define Topic / Sub-topic of module )
Structure of sporophyte (Foot, Seta & Capsule) Liverwort Sporophyte Hornwort Sporophyte Moss sporophyte
Systematic I (Bryophytes) Botany Diversity in Sporophyte
Sporophyte Sporophyte is a dependent and diploid phase in the life cycle of Bryophytes. It is always attached to the gametophyte and nutritionally dependent on gametophyte due to lack of chloroplast. They are relatively small. They have no lateral appendages or branching as found in gametophyte. There is no mean of apical growth hence they are of determinate growth. However in hornworts the sporophyte is of indeterminate growth due to basal meristematic zone. The main function of the sporophyte is to produce spores as well as to disperse them to distant places for successful completion of life cycle. Accordingly they have adapted such morphology which is well suited to perform their ultimate function. The term sporogonium is often used for the bryophyte capsule as well as for whole bryophyte sporophyte. Nutritional dependency of sporophyte on Gametophyte: As far as nutritional dependency of sporophyte on gametophyte is concerned, the sporophytes are described as totally dependent on gametophyte and at times parasite on gametophyte also but it is not exactly true as chloroplasts occur in the capsule wall, seta and foot cells also (Müller1954, Watson 1964). In liverworts, the sporophytes are more dependent on gametophyte as they are poor in chlorophyll contents and they lack stomata. However, there are many liverworts in which the sporophytes are capable for photosynthesis at least in early stages of development as chloroplasts are present in foot, seta and capsule wall cells e.g. Marchantia polymorpha, Dumortiera, Riella americana, Sphaerocarpous texanus, Monoselenium tenerrum, Pellia epiphylla etc. (Bold 1938, 1948, Studhalter 1938, Müller 1954). In hornworts the sporophytes are green throughout the life. The capsule wall has chloroplast and functional stomata. Hence, they are not fully dependent on gametophyte. As such the sporophyte is not a free living structure, however there is a report of independent growth of sporophyte even after the death of Gametophyte, in Californian hornwort: Anthoceros fusiformis (Campbell 1924). In mosses the sporophytes are photosynthetically functional for a longer period of their lives as they have spongy green tissue and stomata which are mainly confined to apophysis region.
Systematic I (Bryophytes) Botany Diversity in Sporophyte
Structure of Sporophyte: The sporophyte in Bryophytes is differentiated into three parts: Foot, Seta and Capsule.
Foot: Foot is the basal portion of the sporophyte. It is an absorbing and anchoring organ which remains embedded in the gametophytic tissue. It is haustorial in nature and derives nourishment for developing sporophyte. It may be variously shaped being globose, bulbous, conical, acuminate and sometimes anchor shaped with extended edges which deeply penetrate in gametophytic tissue. It is commonly present in all the bryophytes. Exceptionally it is absent in Riccia. The foot is globose (in Anthoceros, Corsinia, Targionia), globose anchor shaped (in Marchantia, Pellia), acuminate (Calobryum) and dagger-like (in mosses). The foot is an important and vital organ of sporophyte as its main function is absorption of water, inorganic ions and nutrients required for the growth of the sporophyte. It has a mass of cells which are generally undifferentiated in thalloid liverworts and slightly differentiated in leafy liverworts. However in mosses the foot cells are differentiated into outer haustorial cells called as ‘Transfer Cells’ and inner unspecialized cells with central conducting cells.These transfer cells are present at the junction of gametophytic and sporophytic tissue on both the sides. They are specialized cells for efficient transfer of nutrients by cell wall labyrinth. The labyrinth is formed by infoldings and growth of the cell wall material in to the protoplast which increases the surface area for absorption. By osmosis water is transferred from transfer cell of gametophyte to sporophytic tissue. At maturity of the capsule, cell wall labyrinth is filled with new wall material and looses the ability to transfer nutrients. Then foot changes from an absorbing organ to anchoring organ (Hébant 1975). In Liverworts the foot is generally wider than the seta while in mosses the foot is not wider than seta but gradually becomes narrower, tapered and deeply penetrated.
Seta: The seta is a stalk like structure which holds the capsule. It may be short, massive or elongated and rigid. Sometimes it is absent also as in hornworts and few liverworts like Riccia. The length and movement of seta help in the dispersal of spores. The seta is variable in different groups. Liverworts: In some liverworts the seta is very small, narrow, highly reduced to few celled broad as in Sphaerocarpous, Corsinia and Riella. It does not elongate even after the maturity. While in
Systematic I (Bryophytes) Botany Diversity in Sporophyte
majority of liverworts the seta is small at initial stage but after the maturity of the capsule it elongates rapidly pushing the capsule outside the protective coverings: calyptra, perianth, perichaetium or involucre and helps in the spore dispersal e.g. members of order Jungermanniales and Metzgeriales.
Cross section showing embedded sporophyte, Riccia thallii
Foot Capsule Seta Marchantia Cross section of sporophyte Pellia: Capsule, Seta http://botweb.uwsp.edu/images/SPLab/m aster/1233.jpg
In Pellia the seta elongates at the rate of 1mm per hour and attains a length of 5 cm (Watson 1964). Monoclea is also an exceptional genus having a long seta. In the order Marchantiales the seta generally remains small throughout. The capsules (Sporophytes) are present on the lower (ventral) side of archegoniophore and they are inverted and hanging. In Riccia the seta is totally absent. The seta is generally composed of thin walled cells but the seta anatomy may be variable. It may be differentiated or undifferentiated, massive type or with fixed number of cells having8+4 seta anatomyin (Cephalozia, Cephaloziella), sometimes articulated also as in the family Lejeuneaceae with 12+4 or 16+4 seta anatomy. Hornworts: In hornworts the seta is entirely absent. It may be represented by mere a constriction in between capsule and seta. Mosses: In all the mosses the seta is relatively very long and stout or rigid with well differentiated outer cortical and inner central conducting region. It develops gradually and attains its full length before the maturity of the capsule. It is recorded up to 5 cm long in Polytrichum commune and up to 7 cm long in Pohlianutans. In cleistocarpous mosses, the seta is short (e.g. Ephemerum and Phascum), while in some other mosses the seta is totally absent (e.g. Sphagnum, Andreaea). In these mosses the capsule is raised by means of leafless gametophytic axis (pseudopodium) which develops after the maturation of capsule due to meristematic activity.
Systematic I (Bryophytes) Botany Diversity in Sporophyte
Capsule:The capsule is main fertile portion of the sporophyte which is often termed as sporogonium also. It is of variable shapes:Spherical or globose (Sphaerocarpous, Riccia, Pellia, Fossombronia, Sphagnum and most of leafy liverworts), ovoid (Riccardia, Marchantia), elongated (Calobryum, Haplomitriium, Pallavicinia, Trichocolea, Monoclea), cylindrical (Notothylas, Anthoceros), pyriform (Funaria), asymmetrical somewhat feeding bottle shaped (Buxbaumia) andumbrella like (Splachnum). The structure of capsule is slightly different in liverworts, hornworts and mosses however basic structure is same having capsule wall enclosing spores. Liverwort Capsule: The liverwort capsule is of determinate growth. It has 1-many layered capsule wall. The stomata are totally absent. In the orders Marchantiales, Sphaerocarpales and Calobryales the capsule wall is unistratose while in Jungermanniales and Metzgeriales it is 2-many layered. The cells of the capsule wall is either thin walled throughoutor has characteristic thickening patterns: (i) Nodular thickenings - present at the corners or angles of cells or (ii) Annular thicknings - present on the end walls, radial walls or tangential walls. The thickening in the capsule wall cells plays an important role in the dehiscence of the capsule which is mainly 4-valved in liverworts. Sometimes there may be 2-4-valved dehiscence or irregular dehiscence (Marchantia). Besides in few members of the family Aytoniaceae (Plagichasma, Reboulia) the capsule dehisces through a lid or operculum. While in few taxa, there is no special dehiscence mechanism and the capsules are cleistocarpous where the capsule wall and surrounding tissue disintegrate releasing the spores. In most of the liverwort genera the capsule has spores and elaters. Spores: The spores are fertile cells which are haploid and are the first cell of the gametophyte. They may be of three types: Polar, Apolar and Cryptopolar with or without triradiate mark. They are spherical to tetrahedral in shape with various sporoderm patterns. Elaters: The elaters are the sterile cells. They are generally elongated and tapered at both the ends with 1-2 (3 or 4) spiral thickening bands: single spiral thickening band (Riccardia, Stephensoniella, Frullania), two spiral thickening bands (Marchantia, Pellia, Calycularia), three-four spiral thickening bands (Athalamia, Mannia). These elaters are generally free as in the genus Marchantia or sometimes they are attached to the wall of the capsule with their narrow end as in some leafy liverwort (e.g. Frullania, Lejeunea). Besides normal elongated elaters, few short and stumpy elaters are also present in some genera of order Marchantiales.In some members of the order Metzgeriales, a central mass of elongated sterile cells (elaterophore) is also present which may be fixed at the base (basal elaterophore in Pellia), or at the
Systematic I (Bryophytes) Botany Diversity in Sporophyte
apex (apical elaterophore in Metzgeria, Riccardia). The elaters are absent in Riccia and the capsule has spores only while in Sphaerocarpous, Corsinia, the capsule has spores and some rounded sterile cells called as nurse cellswhich are nutritive in function. Elaters are absent in these genera.
Hornwort Capsule: The hornwort capsules are indeterminate in growth. They continue to grow due to basal meristematic tissue. They are needle or horn like, cylindrical in shape with multilayered capsule wall, spores, elaters (pseudoelaters) and central sterile column called as columella. The stomata are generally present in the capsule wall (Anthoceros, Phaeoceros and Folioceros) while they are absent in Notothylas, Megaceros and Dendroceros. The columalla is present in most of the hornworts but it is absent in few species of Notothylas (N. levieri, N, pfleidereri, N. khasiana). The spores are variable with different sporoderm pattern. In hornworts the elaters are 4-celled in contrast to single celled elaters in liverworts. The normal elongated elaters with spiral thickening bands are present in Megaceros and Dendroceros while 1-3 celled, short stumpy pseudoelaters are present in Anthoceros, Phaeoceros, Folioceros and Notothylas.
Hornwort (http://botit.botany.wisc.edu/images/130/Fern_Allies/Lycophyta /Club_mosses/Lycopodium_vs_Huperzia.low.jpg ) Hornwort Sporophyte
Systematic I (Bryophytes) Botany Diversity in Sporophyte
Moss Capsule: The moss capsule is of determinate growth. It has multilayered capsule wall, spore sac and central columella. Stomata may be present or absent in the capsule wall. A typical moss capsule generally has three main parts: Apophysis, Theca and Opercular region.
ffoot
Capsule
Seta
Peristome
Gametophyte
Moss Sporophyte (Glime, J. M. 2013. Ecophysiology of Development: Sporophyte. Chapt. 5-9. In: Glime, J. M. Bryophyte Ecology. Volume 1. 5-9-1 Physiological Ecology)
(i) Apophysis: Apophysis is the basal sterile portion of the capsule which may be indistinct (less developed e.g. Pogonatum) or distinct (well developed e.g. Polytrichum). It is much prominent and greatly expanded in Splachnumampuullaceum and umbrella like in Splachnumluteum. (ii) Theca: The theca is main fertile region of the capsule. It has multilayered capsule wall, spore sac and central columella. The spore sac is generally present all around the columella (in most of mosses) which is attached to the capsule wall on outerside and to the columella on innerside by means of outer and inner trabeculae respectively. In some mosses the spore sac is dome shaped which arches over the columella (e.g. Sphagnum, Andreaea). The columella is generally present throughout but it is absent in Archidium. The spores are generally small and present in large number. In few taxa like Ephemarum the spores are very large and very few in number. (iii)Opercular region: The apical portion of the capsule is opercular region. It consists of operculum, annulus and peristome. The Operculum is a lid or cap at the capsule mouth whichis present in most of the mosses. At maturity, it gets removed. The operculum may be absent in few mosses like Andreaea, Takakaia. The Annulus is the junction point of operculum and theca. It has a ring of thin walled delicate cells which helps in the removal of operculum at maturity. The Peristomeis taxonomically very important. It is present at the capsule mouth below the operculum.
Systematic I (Bryophytes) Botany Diversity in Sporophyte
It has a fringe of peristomialteeh. The number of teeth may vary. Either they are 4 or multiple of 4, i.e.16,32, 64. They may be present in one or two rings and help in spore dispersal. The peristomial teeth are of two types: Nematodontous or Arthodontous. The Nematodontousperistome consists of several concentric layers of entire thick walled elongated cells. They are 16-32 or 64 in number and present in a ring. This type of peristome is found in the members of order Polytrichales (Polytrichum, Pogonatum). The Arthodontous peristome consists of locally thickened periclinal wall pairs. The plates constituting the outer (dorsal) and inner (ventral) faces of the teeth are derived from the rest part of the contributing cells which remains present after the breakdown of cells. This type of peristome is found in most of the members of Bryales. They are present in one (haplolepidousperistome) or two (diplolepidousperistome) rings. The peristome teeth are absent in the orders Sphagnales, Andreaeales and Takakiales.
Sphagnum Andreaea Takakia (www.aamaljudaibi.kau.edu.sa)( (www.biologados.com) (Phytoimages.siu.edu)
Arthodontous Peristome (Haplolepidous, reduced) (Glime, J. M. 2013. Ecophysiology of Arthodontous Peristome (Diplolepidous) Development In: Glime, J. M. Bryophyte Nematodontous Peristome Ecology. Volume 1.) (www.flickr.com) (www.blogs.ubc.ca)
Systematic I (Bryophytes) Botany Diversity in Sporophyte
Spores & Elaters (Liverworts) (Glime, J. M. 2013. Ecophysiology of Development In: Glime, J. M. Bryophyte Ecology. Volume 1.)
Systematic I (Bryophytes) Botany Diversity in Sporophyte