Fisiologia De Hongos

Fungal Physiology

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Joseph GH Wessels, University of Groningen, Haren, The Netherlands
. Introduction

Fungal physiology is concerned with activities related to growth, development and
reproduction of fungi. These activities can only be understood with reference to the
structure of these organisms.

. Nutrient Acquisition
. Central Metabolism
.Cellular Responses to Nutrient Concentrations
. Cellular Responses to Temperature

Introduction

doi: 10.1038/npg.els.0004305

It is now recognized that fungi constitute a separate kingdom equivalent to that of Plantae and Animalia. By comparing differences in 18S ribosomal-ribonucleic acid
(RNA) sequences, a phylogenetic tree was constructed
(Cavalier-Smith, 1993) in which the Fungi appear asa
monophyletic group comprising Chytridiomycetes (Chytridiomycota), Zygomycetes (Zygomycota), Ascomycetes
(Ascomycota) and Basidiomycetes (Basidiomycota). Fungi defined by their 18S ribosomal and protein-coding sequences (Baldauf and Palmer, 1993) appear more related
to animals than to plants. Also some biochemical characteristics point that way. For instance, fungi contain in their
cellwalls, 1,4b-linked poly-N-acetylglucosamine (chitin),
also widely occurring in animals but absent in plants.
Fungi and animals use glycogen as a storage polymer but
not starch, unlike plants. Furthermore, the nonreducing
disaccharide trehalose is widely used by animals and fungi
whereas plants use sucrose as a transport carbohydrate.
See also: Chitin; Fungi and the history of mycology;
Fungalcell walls
The fungal kingdom thus defined (Eumycota or true
fungi) excludes some groups traditionally studied by mycologists. The slime moulds (Mycetozoa) now find a place in
the kingdom Protozoa. These organisms, which resemble
fungi when they form spores, are phagotrophic (ingestion of
food particles by phagocytosis), unlike in true fungi, which
only take up small molecules. The Oomycetes(Oomycota),
to which belong important parasites of plants (Phytophthora and Pythium) and fish (Saprolegnia), and
Hyphochytridiomycetes (Hyphochitridiomycota) have a
completely different ancestry from the true fungi. Together
with certain algae and diatoms they are grouped within the
kingdom Chromista. Their distinctiveness from true fungi is
also evident from biochemical data. They have wallscontaining cellulose (like plants) and synthesize the amino acid
lysine by a route shared by plants and bacteria but different
from that in fungi. Their plasma membrane does not contain ergosterol, the typical sterol of true fungi (animals have
cholesterol, plants a variety of other sterols). Yet, at some
time in their evolutionary history the Oomycetes evolved a
life style, including apicalhyphal growth, very reminiscent of true fungi, and therefore they are often called
pseudo-fungi. See also: Amino acid biosynthesis; Cellulose:
structure and distribution; Slime moulds

Although the fossil record is scant, it shows that fungi
arose in the Cambrian (about 500 million years ago) at the
same time as plants and animals, probably as a separate
and unique strategy of life. Assummarized by Hawksworth (1991), the earliest hyphal fungi probably lived as
primitive lichens in symbiosis with cyanobacteria (which
photosynthetically assimilate both carbon dioxide and nitrogen) in the porous surfaces of rocks. With the advent of
land plants in the late Silurian and lower Devonian (about
400 million years ago), fungi are found inside these plants,
possibly in a mycorrhizalsymbiosis, and they may actually
have been responsible for the colonization of the land by
plants. Basidiomycota are not documented until the Carboniferous (about 300 million years ago). Since they are the
chief decomposers of plant remains their scarcity at that
time may have been a factor in the formation of extensive
coal deposits. It can be calculated that at present in the
absence of these...