Salient Features of Fungi PDF

25 INTRODUCTION DEFINTION: (General characters of fungi) The branch of science that deals with the study of fungi is called Mycology (Greek words mykos =mushroom; logos =iscourse). The fungi (singular-fungus) include all thos...

25 INTRODUCTION DEFINTION: (General characters of fungi) The branch of science that deals with the study of fungi is called Mycology (Greek words mykos =mushroom; logos =iscourse). The fungi (singular-fungus) include all those plants whose form is a thallus (i.e., not differcntiated into true roots, stem and lcaves) that lack chlorophyll (the pigment responsible for synthesis of carbohydrates from carbon dioxide and water, i.e., photosynthesis). Absence of chlorophyll is the one character on the basis of which the fungi can be distinguished from rest of the plant kingdom. However, all those plants which do not possess chlorophyl (e.g, a red algae-Harveyella mirabilis, many colourless bacteria and many parasites flowering plants, suchas Orobanche, CuSCuta, Rafflesia, etc.) can not be called fung. Thusa correct definition of fungi that excludes allother organisms may be given as, "a group of those plants whoseform is a thallus, build up of single cellor cells that possess definite cell wall and nucleus but lack chlorophyll and differentiation of vascular tissues". This definition does not include bacteria(due to lack of nucleus)and slime moulds (due to lack of cel wall). However, some mycologists ínclude slime moulds as a separate group- Myxomycetes along with fungi. HABITAT (Occurrence) : Fungiis a large group includes more than 1,00,000 species distributed throughout the world. They are ubiquitous and occur in almost every habitat where organic material is available. Since they lack chlorophyll and cannot perform photosynthesis, they do not require light for active growth and metabolism. They can occur in light as well as in dark, but the presence of external source of organic food is required for normal growth. Fungi flourish well in moist, dark and warm conditions but their presence at or below Ireczing tlemperature as well as in hot deserts has also been reported. In fact afew spores and conidia can survive even in comnpletely dehydrated condi tions. The most usual habitat of fungi is wet soil rich in humus. The forms TOWing in such habitats are considered advanced (examples, Agaricus, Morchella, Peziza, etc.). A few forms are aquatic (example, Saprolegnia). These are considered primitive. Some are subterranean. Most of thefungi grow and contaminate the foodstuffs such as bread, jams,pickles, fruitsand Vegetables. Some contaminate the drinking water. ng grow as parasites on plants as well as on animals and cause serious diseases in man such as candidosis diseases. Some fungi also cause caused by Candida nchophyton, albicans),etc.), Epidemophton. dermatomycosis aspergillosis(caused by Microsporm, (caused by Aspergilhus sp.),etc.  154 olism. norcanic NUTRITION:ycohia terotrophic func (Greekalgal hostinfestans,under and roffsi). dead isgrow Phytophihora Erysiphe, in divided to TheThus, way parasites complete cxisting itcatingbecomedead truedead organic organisms. rotten.mycorrhiza. into ofHABIT derives Fungi Iivespartncrs Some orThe pass (b) advance as living (a) parasites 2. saprophytes. and (b) decaying ) 1.two nutrition. The in certain (e.g., biotrophs obligateObllgte these Parasites beside Saprophytes Itbroad eadoparasites symbiotic parasites Facultative bost an in Facultative Obligate parasites. matter. includes fungal(Mode nutricnts are in fungi most ctc.); which an decaying and leaf their organism essential Thus, fewTheyA wever, symbiotic tissues. ar e intimate another. incapable in beneit growcircumstances of then spot (ü) life : organic The categories members of their th e but obtain parasites parasites further The Examples, saprophytes allaccording formseither life) association may saprophytes: fungi) get cycles They association Examples, parasites organic saprophytesthose The : from when in life Hemiblotrophs continue grow part teA rm matter : amode association words mykos =cach defomans, Taphrina beetc. their their live lew the of synbiotic other.ectoparasites cycle and fail : sub onparasite of matter, fungiterm - inlive lack grow thcy nourishment (Examples food into They dividedliving derived th e is Pythum. TheyPeziza, : and : to on ung cernal synthesiZing of with in chlorophyll issymbiotic nutriton. (ii) to to materials It which arederived their dead heSZe wiAnotber th association inside association can It develop : threegrow are with may but includes can alga Perthotrophs They from organism Morchella, are furtherobtain SOurce the alsoincludes the into another be from not modedecaying Mushroom; -Albugo,categories on ordinarily under Thetheir rootscxample in thewhen Lichens host saprophytically andatack artíficial grow the true fodefined r Greek growfungi sub fromassociation and ofINTRODUCTORY wi th and it s their part afofungi r with grow fungi sporulate living parasitesexistance" living certain Agaricus. on Greeknutritionorganic exhibit owa of organism. as living whi divided ch food their ofneed higher hizg where ofother saprophytes. th e They Puccinia, : - obtain saprophytes living as word with on which tissues media.) organism an word their food. symbiotic normal plants(e.g, living tissues conditions get from beterotrophic matter both =root) external kilafter Blotrophs and their organism (Thrower, parasites host, into Sapros theyother otein, They organisms. both host. live (e.8, Luttrell on restricted food their dead- BOTANY the Sphaerotheca, ie., are growth association as Sclerotuum host the which the in from andgrow food meaningclassificd on plants or organic where fungal surface Eramples, parasites tissue However, arce tissue from meaning or they they decaying fat Pinus). same they The(19n4): only 1966).whichvirus from ormode living VOL and and and thus, the and Tbey may on are as of is it. I INTRODUCTION tissucs bostofumcs calicd absorbedwhich (interccllular) penctrate magnesium, ganeseBesides, solubleparasites hyphaesome amino suited materials peptides, of carbon vitamin hormones. growth carbon. Fungi Most the INTRACELLULAR breakspecial frequirements. or baustoria. uar Fig HYPHA nutrients into and have many Nitrogen requirement. as almost 25.1. into by of parasitic the the molybdenumgrow etc.external the phae; orthe thabsorbing e (Fig. Different HAUSTORIUM complcx occursspecific substratum. best mineral are acids) all fungi penctrate host mycclium. 25.1).Thesefuni B. A requirement fungi. Intassociationsof eroelluler in necded source. Simple tissucs. requirement medium slightly acidic elements and need Most haustoria molecules simpler through intoorgans. are inorganic However, produce into They Hydrogen as external theof sugars Parasitic They macronutrients required sPhae absorb HAUSTORIA the citber Usually the secrete of such fulfilled is th e such fungi special -HOST CELS HYPHA host INTERCELLULAR wholenutrients (such asand yeasts source syathesize Ectoparasite. fungi as as the cells remain tmicronutrients. he sulphur, oxygen asglucose, by intracellular mycelium both of solublc may saprophytes penetrate nitraterequire (intracellular).extracellular The sometheir around and and enzymes forms. carbohydrates with in iron, arorganic phospborus, e their host remain the attack fructose, food or pH6. obtained andacetates own cells. intercellular th ey zinc, absorbing from cdoparasite direcly laterare specificSome ammonium (such requirement A. Absorption may copper, as the Intacef. Most potassium, from asthe etc. to cell develop hosts. obligale protcins, armeet e ongans, spacesof water.salts) source saps the or man best the 155 of oB  1$6 Synchytriun). reticulum,theretiatedother The Somecalled SOMATIC In rue cell The mostroot, The arerelated into unicellular byphae olipore. Septum th Fie, B4avotie wiphae; wall hyphae ofplant 25.2. Goliother plasma thestem OR Multicellular compound. is hypha;Different H G NUCLEUS A cytoplasmiccomposed NUCLEUS (singular-hypha). are cases, andbody VEGETATIVE apparatus VACUOLE membrane, long forms leaves). of H.forms thallus fungi O0.o NUCLEUS The of and tinucleate byphae; septateF.of inchusions and celtubular. fungal l theconsists The is funl cytoplasm, wall mycelium thSTRUCTURE ribosomes. typically e thallus SEPTUM thalli.A. WALL B cellulose,They mass of cels; PonÉ encloses such thalloid may long, of are nucleus is INTRODUCTORY be BOTANY OFVOL.I NUCLEI Hyphae I. Unicellular The as hyphae Septum pectose, made unicellular protoplast completelytubular, (ie.PLANT , uninuckeatewith SEPTUM mitochondria, reserve PARENTHOSOME with form; up is not E callose, of branched called BODY food whichdefinite differentiated simple Y:J vacuoles. Besides, or CoenocyticB. PORE endoplasmic chitin multicellular. (Fig. absent myceliun. pore;cells;G. material is differen orcel filaments 25.2): J. walls. (e,g, is any In into INTRODUCTION Where Plasma Whereas peripheral. fibrils. lowerFlagella flagellum homokaryotic mycelium- mycelium (dikaryotic) with cap-likedolipore Basidiomycotina the tum. situated and divided from multinucleate. nucleate condition the glycogen AXONEME Presence Each pore It one Usually the entire the representation tonematic) Fig The fungi. by membrane, O the has (Fig. thickenings are bears iscentrally.order is of or flagella all 5.3. APPENDAGES HAIR LIKE LEND PIECE cell a cell cross called mycelium oil The two These orswollen. barrel the mycelium eucaryotic entire Plagella B EHAIR. EMER 25.3)primary of a binucleate cells. or of centrally -Uredinales Such droplets. type.CYTOPLASMIC EFLIM two centralflagella singlet multinucleate. heterokaryotic. a except intoSuch septawalls, are of SHEATH are :multicellularcalledshaped acellular a The 9+2 t.C-F. s. in central mycelium The possess condition the and monofibrillar. corethin, in located Uredinales) the is In offungi. openings a called thsome flagella. typical flagellum arrangement D fibrils motile pore septum condition other. e Different A. known parenthosome. (Basidiomycotina) coenocytic. central fibrils hair-like Both cross Whiplash m are bodies mycelium wi doliporeth aseptate. where lower This 9+2 withSome showing9+2types of Theallows pores. is walls are central as the poreopen is called the fungi, arrangement (acronematic) arrangement of of extensions uninucleate axoneme. is highernuclei more If sometimes the on(Lat. septum the (septa)are The fibrils lagellation; CENTRAL SINGLET FIBRIL may ends. Each mycelium the the and characteristic both complex, cytoplasm septate aseptate arrangement PERIPHERAL DOuBLET FIBRIL fungi ofbe dolium The possess cytoplasm cvtoplasm G nine It of septum is type; uninucleate, a th e of is of is andmyceliumis not sidesedges called surrounded enclosed cell cells dikarotic produce notfibrils G. composed doublet higher = single aseptate Diagrammaticof B. and a multicellular. of found fibrils. Tinsel cytoplasm. and of Euascomycetes offormed. is feature are large is by two cell nuclei septa fungi simple mycelium continuous dolipore inthe by (pan fibrils of secondarybinucleateguarded jar). and bacteriacharacdouble a of kinds may is sheath elevenEachsome around to usuay Such muid are by The sep(e-g-,passpore ofbe 157 s a in  INTRODUCTORY BOTANY VOL.I INTRODUCIION 159 158 are either uniflagellate or biflagellate. There PERITHECIA The motile bodies of- fungi the tinsel type. The CENTRAL CAVITY type and (i) flagella () the whiplash ending into a narrow end piece. are two kinds offlagellum whiplash type of is flexible and long lagellum. The tinsel type It has smooth surface. It is also called acronematic fine hair- faoges like (hairy) and bears is also called of flagellum is usually small nastigoneme. This type of it is HYPHAL called immer hairs or body bears two flagella of equal length, CORE pantonematic. If a biflagellate equal it is called beterokontae. GELATINOUS called isokontae. If they are not LAYER Modification of nycelium : organized and appear just STROMATIC In some higher fungi, the mycelium becomes compactly woven tissue-like TISSUE It consists of loosely or like a thalloid body. 25.4). There are two types of plec -STALK structure, called plectenchyma (Fig. B LOOSE HYPHAE tenchyma lie almost of loosely woven hyphae which PSEUDO PARENCHYMATOUS () Prosenchyma : It consists HYPHAE parallel toeach other and the cells and hyphae are clearly distinguishable. SCLEROTIUM (ü) Pseudoparenchyma : It consists of comnpact mass of parench yma-like tissue where the hyphae are very closely packed and inter these wOven. In cross section, isodiametri A nyphae appear as D E PSEUDOPARENCHYMA Fig. 25.5. A. Sclerotia in ryeRhizomorph; Besides plectenchyma, B B. LS. of rhizomorph tip; C. LS. of there are other modiications PROSENCHYMA grains; E. Single sclerotium; F. T.S. of sclerotium. stroma; D. of mycelium such as Fig. 25.4. Organisation of mycelia in fungi. vegetative cell may be transformed into reproductive body rhizomorph, sclerotia and portion of vegetative thallus is (holocarpic). If a stroma. several hyphae condition is called eucarpic. transformed into reproductive structure, the (i) Rhizomorph (Fig. 25.5): In some higher fungi,string-like or root [A]ASEXUAL REPRODUCTION: with each other and form cord-like, become interwoven rhizomorphs. These structures serve The kind of reproduction which does not involve meiosis and likeelongated mycelial strands called nucleiis called asexual fusion of the functions of root. compact mass of interwoven reproduction. It occurs by the (1) Fragmentation : The fungal mycelium gets followinginto methods - (iü) Sclerotia (Fig. 25.5) : It consists of a hyphae become hard and Iragments accidently or through external force. Eachbroken smaller pseudoparenchyma. The outer hyphae forming form a protective covering or rind. These bodies remain dormant under favourable conditions. develops into a new individual. This type of reproduction isfragment (piece) very common in unfavourable conditions and germinate at the onset of fungi. which a large (iü) Stroma(Fig. 25.5): It is a thick mycelial mat on or, in (2) Budding (Fig, 25.6): The parent cell produces one or more bud-like number of fruit bodies (fructifications) develope. protuberances which detach from parent cell and grow into new individual. REPRODUCTION: Such type of reproduction is very common in budding yeast (Saccharomyces) type of where chain of buds may produce pseudomycelium. Fungi generally reproduce by asexual and sexual methods. The reproduction called vegetative is included under the category of asexual (3) Fission (Fig. 25.6):The parent cell splits into two equal halves by a Constriction and formation of cell wall and each half develops into a new reproduction. ndividual. Fission is very common in bacteria and also 0ccurs in yeasts. In fungi, the reproduction typically occur by production of spores (asexual and sexual) but other kinds of reproductive bodies may also be (4) Oidia (Fig. 25.7):The bypha breaks up into its component cells or formed in some cases. If the plant body (thallus) is unicellula, the complete Small pieces which behave like spores. These are called oidia. The oidia are  INTRODUCTORY BOTANY VOL.I 160 INTRODUCTION 161 DEVELOPING BUD BUD NUCLEUS VACUOLE sPORESO O SPORANGIUM ZOOSPORES MOTHER CELL D B DEHISCED SPORANGIUM COLÙMELLA VACUOLE NUCLEUS ZOoSPORANGIUM HovDED CELLS A B C D F pIviDING C¸L G SPORANGIOPHORE E cONIDIA Fig. 25.6. AD. Budding,E-H. Fission. CHLAMYDOSPORE STERIGMATA CONIDIA OIDIUM J MEULAE VESICLE E CONIDIOPHORE CONIDIOPHORE F Fig. 25.8. Common types of asexual reproduction. A-C. Spores; D. Zoospores; E-G. Conidia. HYPHAE () Sporangiospores : These spores are produced inside the sac- like structures, called sporangia. Sometimes these spores are also termed as endospores. If the sporangiospores are non- motile, they are called D aplanospores (e.g, Mucor, Rhizopus). If the sporangjospores are motile, they A B are called zoospores. The zoospores may be uniflagellate or biflagellate. Fig. 25.7.A-B. Oidia formation; C-E Formation of Chlamydospores. (ii) Conidia : These are non-motile spores produced singly or in chains generally thin walled and do not store reserve food material. They germinate by constrictions at the tip orlateral side of special hypha! branches, called immediately after liberation and can survive under unfavourable conditions. conidiophores. They are produced exogenously (not enclosed withinsporan These are thick walled resting cells gia). The conidia germinate directly by givingout germ tubes. Sometimes the (5) Chlamydospores (Fig. 25.7) : They store reserve food material and conidia behave like sporangia and called conidiosporangia. produced in the same manner as oidia. withstanding long unfavourable conditions. (B] SEXUAL REPRODUCTION : are capable of (6) Spores (Fig. 258) : Fungi reproduce most commonly by production Sexual reproduction occurs in almost all the groups of fungi cxcept in of spores. These are minute propagating units which serve in the production Tungi imperfecti (Deuteromycotina). It involves union of two compatible of new individuals. They vary in shape, síze and colour in different individuals Luclei of oppositesex at a definite stage in the life-history of fungus. The and sometimes serve as basis in the classification of certain groups of fungi. Sexual reproduction in fungi completes in three phases () plasmogamy, The asexual spores are of two types- (i) Sporangiospores and (i) Conidia. (ü) karyogamy and (iii) meiosis.  INTRODUCTORY 162 fusion of two protoplasts which BOTANY VOL I (i) Plasmogamy : It is the compatible nuclei close together in asingle cell. The resultingbrings as dikaryotizath cell the two becomcs dikaryon. The phenomenon is sometimesoftermed fusion two compatible INTRODUCTION (ii) Karyogamy : It is the nuclei brought 163 together as a result of plasmogamy. The resulting diploidInucleus is caled synkaryon. MOTILE FEMALE GAMETE (i) Meiosis : The diploid nucleus divides by meiosis (or reduction division) resulting in the formation of haploid nuclei. Usually meiosis ocers nuclei. immediately after fusion of two Allthese three phases occur at specific stages in the life- history of funei MOTILE MALE GAMETE In most of the lower fungi (Mastigomycotina and Zygomycotina),the plas ISOGAMETES mogamy is immediately followed by karyogamy and meiosis. In some cases the meiosis is slightBy delayed (Zygomycotina). In case of higher fungi NON MOTILE FEMALE GAMETE (Ascomycotina and Basidiomycotina), the plasmogamy is not immediately followed by karyogamy. In Ascomycotina and Basidiomycotina, the plas B mogamy results in the formation of dikaryon. The two nuclei remain together in adikaryon and divide by conjugate division. It results in the forrmation of dikaryotic phase of life-cycle offungus. The karyogamy occurs at alater stage in the life history which is soon followed by meiosis resultingin the formation Fig, 25.9. Planogametic of haploid sexual spores- ascospores in Ascomycotina and basidiospores in B. Anisogamous; C. OogamousyPe ot sexual reproduction. AIsogamous: Basidiomycotina. (2)Gametangial contact (Fig. 25.10) :It is a Fungi may be monoecious (bisexual) or dioecious (unisexual). The tion where the male gametangia are called kind of oogamous reproduc monoecious species produce the two sex organs on the same thallus or ascogonia. The gametes are non motile antheridia and which female oogonia (Homothallic) whereas the dioecious species produce them on separate FERTILIZATION aplanogametes are never TUBE FERTILIZATION PERIPUASM thalli (Heterothallic). EMPTY TUBE The sex cells are called gametes which are usually produced in sex-or ANTHEAIDIUM gans called gametangia (singular-gametangium). If the male and female gametes are morphologically indistinguishable, they are called isogametes. 00SPORE If the male and female gametes are different, they are called heterogametes. The isogametes are produced in isogametangia whereas the heterogametes are produced in beterogametangia i.e., the male and female gametangia. The ): male gametangium is usually called antheridium and the female gametan 00GONIUM - gium iscalled oogonium. They are also known by different names in different EMPTY groups of fungi. In some cases, the sex organs are not formed and the sexual ANTHERIDIUM 00PLASM fusion occurs between two vegetative cells. Modes of sexual reproduction : There are various modes of sexual reproduction in fungi, which can be A categorised into the following types (1) Planogametic copulation (Fig. 25.9) : The motile (flagellated) Fig. 25.10. A-B. Gametangial contact type of sexual fusion. gametes are called planogametes. In this category of sexual reproduction released fromgametangia. The male and female gametangia come in contact cither one or both the fusing gametes are motle (flagellated). Planogametic with each other. The male gametangium sends a tubular outgrowth, called copulation may further be grouped under three categories- (i) fertilization tube, that pierces throughgametangium the wall of female gametangium. Male Isoplanogametic copulation -when both the fusing gametes are flagellated nucleus or gamete enters into female through this tube. In this and morphologicaly similar; (ü) Anisoplanogametic copulation differ when mode of reproduction the two gametangia do not fuse with each other. the two fusing gametes are ilagellated and morphologically similar but Examples, Åbugo, Phytophthors, Pychiun, Sphaeroheca, etc. reproduction, in size and (n, Ooplanogametic copulation--when the male gametes arce (3) Gametangial copulation (Fig. 25.11): In this mode of flagellated (called sperms) and the female gamete is non-flagellated (called Lhe two gametangiafuse with each other and lose their identity in the sexual Ovum or egg). act. Examples, Rhizopus, Mucor.  through minute, struc female Ustilago, of between differen mode typ D specialised as with numerous, transferred occurs this Peziza, the ZYGOSPORE treated discussillustra fusion. sexual FUSION In Examples, CELL fusion ain hyphae Somatogamy. : you produce 25.12) and are spermatia the by fungi of HYPHAE FUSING studied type somatic These fungi. dikaryotization. and (Fig. GAMETANGIA fungi C. in SUSPENSORcopulation ASCOGON.UM formed QUESTIONS Spermatisation; of nutrition pycnidia). called Some Pseudogamy) features type or graminis. fungi. ISO - hyphae -TRICHOGYNE following