BIO 201: Botany
KINGDOM FUNGI

 

GENERAL CHARACTERISTICS

Basic features:

    Eukaryotic
    Multicellular with different cell types
    Cell walls of Chitin (except one group)
    Heterotrophic -- food from organic source, secrete enzymes into environment & absorb digested material
        Saprophytic -- dead organisms (most common)
        Parasitic -- living organisms
        Mutualistic -- living with another (symbiosis)

Morphology:
     have branching filaments = Hyphae
         large mass of hyphae = Mycelium
     multinucleate cells = Coenocytic
         Septate: with cross walls
         Nonseptate: no cross walls

Reproduction:
     dispersal commonly by spores --- many types of spores
     most commonly asexual
     sexually produced spores typically are resting spores

Taxonomy: two groups not officially recognized
      Lower fungi -- some place in Kingdom Protista
            nonseptate walls
            spores in small sporangia
            flagellated reproductive cells
            include three groups: Chytridiomycota, Oomycota, Myxomycota
      Higher fungi -- true fungi (Kingdom Fungi)
            septate cross walls
            spores in complex structures
            no flagellate reproductive cells
            include three groups: Zygomycota, Ascomycota, Basidiomycota

 

DIVISION/PHYLUM CHYTRIDIOMYCOTA (chytrids or water molds)

The text puts this group in Kingdom Fungi (pp. 287-288)

Basic features:

    aquatic

    unicellular and coenocytic (multinucleate)
    hyphae are typically haploid (but some diploid) - typically composed of a microscopic sphere (see fig 14-13)
    cell walls of chitin (but some rare reports of cellulose in cell walls?)
    have Rhizoids to penetrate food source

Many are parasitic -- on plants & other fungi
     some are saprophytic

Asexual Reproduction:
     sporangium with single nucleus that splits off to produce a flagellate zoospore with one flagellum

Sexual Reproduction:
      sporophyte with thick walled sporangium, meiosis to form spores; they develop into the gametophyte
          male gametophyte produces male gametes
          female gametophyte produces female gametes
      fusion of two motile gametes to produce a zygote which develops into the sporophyte

DIVISION/PHYLUM OOMYCOTA (water molds & mildews)

The text puts this group in Kingdom Protista (pp. 358-360)

Basic features:

    aquatic
    extensive nonseptate mycelium (unicellular, coenocytic)
    hyphae are diploid
    cell walls of cellulose

heterotrophic: parasites on fish
     plant pathogens
     also initial decomposers of dead insects

Asexual Reproduction:
     hyphae grow, terminal portions of a mycelium pinch off to produce Zoospores, each with two (2) flagella

Sexual Reproduction (see fig 15-52):
      reproductive cells produced by meiosis
         several eggs per Oogonium
         Antheridium long and skinny (clavate)
     Zygote with thick wall = resting Oospore
     growth into sporophyte upon germination

(link to water mold diagram)

 

PHYLUM MYXOMYCOTA (plasmodial slime molds)

The text puts this group in Kingdom Protista (pp. 360-362)

Basic features:

    terrestrial
    no cell walls
    vegetative structure = Plasmodium is diploid (coenocytic) (see photo, p. 343)
        Amoeboid - feed by phagocytosis

With adverse environmental conditions (ex. drought) --formation of a hardened Sclerotium (multicellular resting structure)

Sexual Reproduction (see fig. 15-56):
     sporangium development -- meiosis to form 4 haploid spores
          3 of the 4 spores disintegrate before release
     germination into ameboid cells
          some cells become flagellate
     fusion to form a zygote which later develops into a new plasmodium

 

DIVISION/PHYLUM ZYGOMYCOTA (pin and bread molds)

One of the higher fungi (pp. 288-290)

Basic features:

    terrestrial
    hyphae haploid, septate
    cell walls of chitin
    Saprophytic

    Produced complex reproductive structure = zygosporangium with one zygospore (details below)

Asexual Reproduction:
     nonmotile spores on aerial sporangia
     spores air dispersed
Sexual Reproduction (fig 14-15):
     + & - strains
     when come in contact produce Gametangia
     initiation of process of Conjugation (fusion)
     two (2) haploid nuclei into a common cell and fertilize with a thickened wall = Zygosporangium
     Upon germination:
           1) development of sporangium
           2) meiosis to form spores
           3) development into hyphae of new mycelium

 

DIVISION ASCOMYCOTA (cup or sac fungi)

a higher fungus (pp. 291-295)
Include: morels, truffles, yeasts, dutch elm disease, corn blight (examples, fig 14-18)

Basic features:

    Mainly terrestrial
    Hyphae are septate and monokaryotic (= having one nucleus per compartment)

    produce comples reproductive structure = ascocarp with 8 ascospores (see below)

Asexual Reproduction:
     produce a sporangium-like Conidium (pl.= conidia)  within it are spores = Conidiospores
     some species - no sexual reproduction seen, produce only conidia:
           a) Penicillium - flavoring in cheese (blue, Roquefort, Camembert) (fig. 15-33a, 15-34a)
           b) Aspergillus - aid in fermentation of soybean to produce Tofu (fig. 15-33b, 15-34b)

Sexual Reproduction (fig 14-19):
     1) haploid mycelium; + & - strains
     2) eventual fusion of cellular cytoplasm of two types to produce dikaryotic cells (two nuclei per compartment)
          process of cytoplasmic fusion
= Plasmogamy
     3) cell division of dikaryotic cells to form Ascocarp
          each cell with + & - nucleus
          only exception is that of yeast (which has diploid cells)
     4) eventual production of zygote by fusion of nuclei = Karyogamy
     5) development of an elongate Ascus (pl.= asci) with sterile paraphyses between
     6) subsequent meiosis to produce 8 haploid ascospores
            sexual spores = Ascospores

(link to ascomycete diagram)

Three (3) types of sporocarps:
    1) Apothecium - most common, cup-like (fig 14-18a)
        cup fungi, morels
    2) Perithecium - small flask-shape with small opening (fig. 14-21c)
    3) Cleistothecium - no opening, release by decomposition (fig. 14-21b)

Yeasts: most common Saccharomyces
     single celled, 2n, asexual reproduction by budding
     sexual reproduction: meiosis to from 4 ascospores
         2(+)  &  2(-)
         short period of budding
         fusion of a (+) and a (-) to form the zygote

 

 

DIVISION BASIDIOMYCOTA (club fungi)

Yes, a higher fungus (pp. 295-301)
Include: mushrooms (fig. 14-29a-b), puffballs (fig. 14-33a), earthstars (fig. 14-33d), coral fungi (fig 14-29d), rusts (fig. 14-34), smuts (fig. 14-36)

Basic features:

    Mainly terrestrial
    Hyphae are septate and monokaryotic (= having one nucleus per compartment)

    produce comples reproductive structure = basidiocarp with 4 basidiospores (see below)

Sexual Reproduction (fig 14-25):
     sexual process similar to that of ascomycetes
     1) haploid mycelia of two types (+) & (-)
     2) fusion to get dikaryotic mycelia which develop into sporocarp = Basidiocarp
           some zygotes formed (fertilization)
      immediate meiosis to form 4 Basidiospores on a Basidium (club-like structure) (fig. 19-18)
      wind dispersal

(link to basidiomycete sexual reproduction drawing)

Basidiocarp structure:
      Stipe = stalk
      Cap = enlarged apex -- with gills or pores
      Gills/Pores = structures on which basidia produced

(link to mushroom diagram)

 

SYMBIOSIS INVOLVING FUNGI

Symbiosis = living together

Two types involving fungi:
     1) mutualism - both species benefit
     2) parasitism - one benefits, one harmed

MUTUALISM
     two examples: mycorrhizae & lichens

A. Mycorrhizae are the result of fungi in the roots of vascular plants (pp. 340-344)
     fungus benefits: obtains photosynthates (esp.: sugar)
     plant benefits: obtains minerals (esp.: N, P)
           * increases effective root surface area
           * allows plant to reach more soil volume
     this relationship is most common in poor soils
     mycelium of fungus develops from roots to soil

Two types of mycorrhizae based on type of infection (p. 312-315):
      1) Ectomycorhhizae (sheathing) (fig. 14-45)
          produce compact mantle around root
          grow between root cells of epidermis & cortex
                not into cells, not beyond endodermis
          results in short, stubby roots
          most common in: conifers, oaks, willows which are infected with basidiomycetes
      2) Endomycorhhizae (internal) (fig. 14-43 & 14-44)
          fungal hyphae grow into root cells
          within cell walls, NOT cell membrane
          mainly in epidermal & cortex cells
          most common in angiosperms (ex.: tulip tree) which are infected by zygomycetes

B Lichens are the result of a fungus and an algae living together (pp. 306-312)
     a) the mycobiont - a fungus
           mostly ascomycetes, but some basidiomycetes
           provides a suitable environment & minerals to algae
     b) the photobiont - an algae
           an algae (green) or cyanobacterium
           provide carbohydrate & nitrogen compounds to fungus
     symbiosis allows for them to live in very harsh environments: rock surfaces, tree trunks (fig. 14-42)
           ability to survive related to ability to dehydrate quickly
           fungal surface blocks UV light

PARASITISM
     two examples: Dutch elm disease & ergotism

General comments on parasites of plants:
  sources of infection by fungi: 1) spores; 2) thick-walled zygotes
  entry via: 1) wounds; 2) stomates; 3) lenticels
  severity of infection based on:
      1) resistance or susceptibility of host (genetic)
      2) virulence of pathogen
      3) environmental conditions

A. Dutch Elm Disease - fungus growing on the American elm (Ulmus americana)
     fungus = Ophiostoma ulmi (an ascomycete)
     fungus is carried from tree to tree by the elm beetle
     Life Cycle (please refer to handout from class):
        Adult beetles feed on live portion of tree (A, D)
            fungal spores enter at site of physical damage (E)
        Mycelia grow into vascular tissue, esp. xylem (G)
            produce conidia with condiospores (H)
        Conidiospores transported throughout the tree via xylem
            spores germinate and mycelia spread (B, C)
            xylem eventually blocked causing branch or tree death
        Sexual reproduction with production of ascospores (J, K)
        Adult beetles lay eggs in dead tissue (branches)
            larvae develop galleries (F)
            ascospores germinate and grow in galleries (K, F)
            mycelium develops spores (I)
        As adult beetles emerge they have spores on them
        Spores moved to other tree as adults feed on live branches (A, D)

(link to dutch elm disease diagram)

B. Ergotism (see note on text, p. 307)
     Parasite on fruits of rye (a grain)
         an ascomycete
         contain Lyseric Acid - similar to LSD
     Historically related to several epidemics:
        994: 40,000 deaths in Europe
         1692: possibly cause of witchcraft affair at Salem
        1722: army of Peter the Great, stopping quest of Turkey