This Presentation has been made to explore the cell wall and range of thallus structure & its modification for academic pleasure.

1. MYCOLOGY
PRESENTATION BY:
Dr. N. Sannigrahi,
Associate Professor,
Department of Botany,
Nistarini College, Purulia,
D.B. Road, Purulia
( W.B), 723101,
INDIA.

2. CONTENTS
 Fungi as cell,
 Cell components,
 Thallus organization,
 Thallus modifications,
 Special structure of thallus,
 Cell wall-Structure & Function,
 Ultra structure of cell wall & Composition,
 Conclusions.

3. FUNGAL CELL
 Fungi as ubiquitous in the form of saprophytes, parasites or symbionts
is the eukaryotic in nature with wide diversity as far as the somatic
structure is concerned. The fungi enjoys a wide range as far as
reproduction is concerned and the cellular organizational beauty has
made it unique one in this respect.
 Eukaryotic with distinct cell wall. Cytoplasm & nucleus,
 Uninucleate or multinucleate as coenocytes,
 Heterokaryotic or homokariotic in nature,
 Nucleus contains one or more nucleoli,
 Cytoplasm colorless and granular to reticulate in appearance,
 Cytoplasm contains many big but irregular vacuoles whereas the
higher members contain single large vacuole found in central position,
 Cells contain mitochondria and complex system of internal membranes
including ER, Golgi apparatus,
 Cell membrane contain ergo sterol that replace the cholesterol in animal
cells.

4. TYPICAL FUNGAL CELL

5. THALLUS ORGANISATION
 Unicellular Thallus :
 In some of the lower fungi such as the chytrids, the thallus is more or less a
spherical, single-celled structure . At the time of reproduction, it becomes a
reproductive unit. The latter produces the asexual or sexual cells. Such fungi
are called holocarpic. In them, the vegetative and reproductive stages do not
occur together in the same thallus.
 Plasmodiophora has a vegetative phase consisting of a naked, multi-
nucleate, amoeboid mass of protoplasm. It is termed Plasmodium. The
protoplast of the diploid Plasmodium cleaves to form the resting spores. The
yeasts, which are related to the filamentous forms, also have a unicellular
thallus. In the unicellular holocarpic forms (Synchytrium) the mycelium is
absent.
 Filamentous Thallus :
 The vast majority of the fungi have a filamentous thallus. It originates
through the germination of a spore. The spore germinates as it lands on a
suitable substratum where other conditions of life are also favorable. In
some species, the spore, on germination, produces only a short, tubular
structure of limited growth.

6. RANGE OF THALLUS STRUCTURE

7. RANGE OF THALLUS STRUCTURE
 It constitutes the thallus and is technically called a hypha. The spores of
most of the fungi, however, give rise to a fluffy thallus consisting of a
cottony mass of fine, branched filaments. These long, fine filaments are
called the hyphae (sing, hypha). Some of these hyphae, at a certain stage of
maturity, extend into the air and bear the reproductive bodies.
 The rest spread over or within the substratum and continue the normal
activities. Such fungi are called eucarpic. Collectively the hyphae comprise
the vegetative body (thallus) of a fungus which is called the mycelium. The
hypha is thus a structural unit of the mycelium. It consists of a thin,
transparent wall filled or lined with a layer of cytoplasm.
 The medium upon which the mycelium grows is known as substratum. The
mycelium is the food procuring structure in the life cycle. It carries on the
general activities of a plant cell such as absorption, digestion, respiration,
excretion and growth but not photosynthesis. The hyphae constituting the
mycelium branch, spread in all directions within or over the substratum to
form a loose and ramifying network.

8. RANGE OF THALLUS STRUCTURE
 The hyphae are usually colourless particularly those embedded in the
substratum. The aerial hyphae in some fungi become colored. Black,
orange, yellow, red, blue and brown are the usual tints. The color is usually
confined to the hyphal wall.
 Even when the pigments are present in the protoplasmic contents, they do
not form an integral part of the living matter. The pigments play no role in
the physiology of the fungus. The growth in length takes place at the tips of
the hyphae and is thus termed apical.
 The thallus may be grouped into- holocarpic or eucarpic; When the thallus as a
whole is vegetative as well as reproductive in function- holocarpic but when the
portion of the hyphae of the thallus takes part in reproduction-eucarpic.
 Hyphae- aerial or substrate , both are branched; substrate hyphae for nutrients but
aerial hyphae for reproductive structures, look black, red, blue , green , brown in
color diversity;
 Hyphae may be modified- Prosenchyma, Pseudo parenchyma, Rhizomorph,
Sclerotia, Sporophore, Stroma etc depending on species diversity.

9. KINDS OF MYCELIUM
 The fungus mycelium in fact, is a multinucleate structure lacking
complete internal cell boundaries.
 i. Aseptate Mycelium- In algal fungi, it is multinucleate, aseptate,
grows terminally by the apical elongation of the hyphae accompanied
by increase in the number of nuclei by nuclear division, becomes
coenocytes.
 Ii. Septate Mycelium- Develop internal cross walls that divide the
hyphae into segments at regular intervals behind the hyphal tip,
segments uninucleate or multinucleate. Formation of septa is always
preceded by the division of nucleus, each has a central pore or rarely
more than one pore although complete partitions do not occur during
vegetative phase.
 Mostly found in the members of Ascomycetes & Basidiomycetes,
 In Basidiomycets, further elaboration of the septum to produce a more
complex pore called dolipore and it is covered by round bracket like
structure – Parenthesome.

10. AGGREGATION OF HYPHAE
 Different types of modifications of hyphae mycelium are found as
follows:
 PLECTENCHYMA-A kind of false tissue formed by the aggregation of
hyphae, may be two types-
 A. Prosenchyma - Rather loosely woven hyphae, hyphae do not lose
their identity, run more or less parallel to each other composed of
elongated cells,
 B. Pseudoparenchyma - The hyphae become woven and intertwined
into a compact mass, hyphal mass appears to be continuous structure
consisting oval cells , resemblance with parenchyma tissue of higher
cells
 RHIZOMORPH- Interwoven hypae to form rope like structure,
 Tightly packed and individual hyphae lose their individual identity,
 Outer hard black external layer of the rhizomporph called rind,,
 Each rhizomorph contains a growing tip,
 Rhizomorphs are perennating structure to withstand adverse conditions.

11. RANGE OF THALLUS STRUCTURE

12. AGGREGATION OF HYPHAE
 SCLEROTIUM- Specially modified mycelium for storage,
perennation and vegetative propagation,
 Compact, rounded. Cushion shaped, cylindrical or irregular object,
 Dense mass of thick walled short hyphae to form
pseudoparenchymatous structure,
 polyhedral shape,
 Outer surface dark brown black and crest like,
 It may be pin head to large with several inches in diameter.
 SPOROPHORES- Spore bearing modified into group to form
pycnidia, sporodochia, hymenia, acervuli etc,
 Aerial, erect and arise from the prostrate hyphae,
 Branched or unbranched with sporangia or conidia with them,
 Spore bearing sporophores are sporangiosphores and conidia bearing
called conidiophores.

13. AGGREGATION OF HYPHAE
 STROMATA: The fungal tissue forms a mass of
pseudoparenchymatous tissue like flat or cushion shape structure,
 Several fructifications to form reproductive structures,
 PESUDOSCLEROTIUM
 The sclerotium like bodies are formed at the base of the fruit bodies of
higher fungi,
 In Polyporous basilapiloides formed below the soil surface
 Composed of sand particles surrounded by hyphal aggregations
 APPRESORIUM
 Common in parasitic fungi mostly found in ectoparasites, Terminal
simple or lobed swollen structure of germ tubes or infection hyphal
 Adheres to the surface of the host and helps in the penetration of the
hyphae of the pathogen,
 Found in the parasitic fungi of the orders Erysiphales.

14. APPRESORIUM

15. AGGREGATION OF HYPHAE
 HAUSTORIUM
 Mostly found in the intercellular absorbing structure of obligate
parasites,
 Usually produced in the fungi in which intercellular mycelium formed,
 Vary in shape , may be knob shaped or branched finger shaped,
 Secrete certain enzymes which hydrolyses the proteins and
carbohydrates of the host cell and absorb the nutrients from the host
cell without killing them,
 Provide greater surface area for the exchange of materials.
 In addition to these above kind of modifications, different other
specialized modifications are formed in order to address the stress and
other issues appear in course of their survival and reproductive
potential.

16. HAUSTORIUM

17. CELL WALL COMPOSITION
 The fungal cell wall is located outside the plasma membrane and is the cell
compartment that mediates all the relationships of the cell with the
environment.
 It protects the contents of the cell, gives rigidity and defines the cellular
structure.
 The cell wall is a skeleton with high plasticity that protects the cell from
different stresses, among which osmotic changes stand out.
 The cell wall allows interaction with the external environment since some of
its proteins are adhesions and receptors.
 Since, some components have a high immunogenic capacity, certain wall
components can drive the host’s immune response to promote fungus
growth and dissemination.
 The cell wall is a characteristic structure of fungi and is composed mainly
of glucans, chitin and glycoprotein.

18. CELL WALL COMPOSITION

19. CELL WALL COMPOSITION
 The cell wall is a specific and complex cellular organelle composed of
glucans, chitin, chitosan, and glycosylated proteins. Proteins are generally
associated with polysaccharides resulting in glycoprotein. Together, these
components contribute to the cell wall rigidity. The synthesis and
maintenance of cell wall involves a large number of biosynthetic and
signaling pathways (Casadevall and Perfect, 1998).
 The cell wall is structured in different layers where the innermost layer is a
more conserved structure on which the remaining layers are deposited and
can vary between different species of fungi.
 Glucans is the most important structural polysaccharide of the fungal cell
wall and represents 50–60% of the dry weight of this structure. Most
polymers of glucans are composed of 1,3 linkage glucose units (65–90%),
although there are also glucans with β-1,6 (in Candida but not in
Aspergillus), β-1,4, α-1,3 and α-1,4 links. The β-1,3-D-glucan is the most
important structural component of the wall, to which other components of
this structure are covalently linked. The β-1,3-D-glucan is synthesized by a
complex of enzymes located in the plasma membrane called glucans
synthases.

20. CELL WALL COMPOSITION
 The chitin content of the fungal wall varies according to the morphological
phase of the fungus. It represents 1–2% of the dry weight of yeast cell wall
while in filamentous fungi, it can reach up to 10–20%. Chitin is synthesized
from n- acetyl glucosamine by the enzyme chitin synthase, which deposits
chitin polymers in the extracellular space next to the cytoplasmic
membrane.
 Proteins compose 30–50% of the dry weight of fungal wall in yeast and 20–
30% of the dry weight of the wall of the filamentous fungi. Most proteins
are associated to carbohydrates by O or N linkages resulting in
glycoprotein. Cell wall proteins have different functions including
participation in the maintenance of the cellular shape, adhesion processes,
cellular protection against different substances, absorption of molecules,
signal transmission, and synthesis and reorganization of wall components
(Bowman and Free, 2006; Ponton, 2008).
 Lipids are found in small amounts, prevent to desiccation of cells,
 Presence of pigments and salts; Melanin is most abundant, important to
protect the hyphen, spores and help in pathogenesis , attachment to the
surfaces

21. CELL WALL COMPOSITION
 Enzymes cross linking the fibrils in the wall are released through the plasma
membrane,
 Wall constrictions take place in the apical cap; the synthesis of chitin and
glucans take place within in 1 mm. in the apex; the rigidity of the wall; is
done by cross linking of polymers,
 The wall contains hydrophobins, glomalins ; Hydrophobins constitute 10%
of the total wall proteins, the amphoetric nature provides an array of extra
ordinary functions and play role biotechnology.
 Glycoprotein includes mannoprotein, galactoprotein, xyloproteins etc.
 The wide diversity of the cell wall composition observed as far as the
diversity of the fungal kingdom as stated below.

22. COMMON WALL CONSTITUENTS IN EACH DIVISION
DIVISION FIBROUS
COMPONENTS
GEL LIKE POLYMERS
BASIDIOMYCOTINA Chitin ,β(1-3),β (1-6)
Glucans
Xylomannoproteins,α (1-3)
Glucans
ASCOMYCOTINA Chitin ,β(1-3),β (1-6)
Lucan
Galactomannoproteins, α
(1-3) Glucans
ZYGOMYCOTINA Chitin , Chitosan Polygluchonic acid,
Glucurosomannoproteins,
Polyphosphate
CHYTRIDIOMYCOTA Chitin, Glucans Glucans

23. REVIEW
 Fungi are heterotrophic either parasites, saprophytes or symbionts,
 Unicellular or multicellular, holocarpic or eucarpic with diverse structural
peculiarity as far as thallus is concerned,
 Eukaryotic with almost all kind of organizational beauty observed,
 Cell wall is diverse type with a fundamental framework in all the aspects,
 The reproduction takes place by vegetative, asexual or sexual means following
the route of plasmogamy, karyogamy & meiosis with haplontic life cycle
pattern.
 Play a very significant role in the sustainability of environment and offers raw
materials for the industrial wheel,
 Play a pivotal role for the deterioration of the productivity of crops both
qualitative and quantitative.

24. THANKS A LOT FOR YOUR CONSIDERATION
 References:
 Google for images,
 Microbiology & Phycology - Mishra & Dash,
 Brook Microbiology of Microorganisms-Madigan, Martinko, Bender,
Buckley & Stahl,
 A Textbook of Microbiology- Chakraborty,
 Microbiology- Pelzer, Chan & Krieg,
 Botany for degree students- Vasistha & Sinha,
 Introduction to Mycology and Phytopathology - Mishra & Dash,
 Different WebPages to enrich content.
 Disclaimer: This PPT has been designed to enrich the open source
of learning. The author does not claim any kind of financial pleasure