Introduction

The cell wall, plasma membrane and tonoplast are major barriers to the movement of solutes into and out of fungi. The wall is very much less of a barrier than the two membranes. Nevertheless it cannot be considered solely as a porous structure that allows through it only molecules below a certain size. The wall has other properties that influence the nutritional behaviour of fungi. These properties as well as the porosity of the wall are addressed below. The consideration of membrane focuses on the somewhat scattered information about the lipid part of the membrane; the various transport systems are dealt with in other chapters.

The wall

Introduction

Our knowledge of the polysaccharide composition of the walls in both filamentous fungi and yeasts covers a wide spectrum of taxonomic groupings and for many species there is much detailed information (for reviews, see Farcaš, 1979, 1990; Gooday & Trinci, 1980; Arnold, 1981a; Wessels & Sietsma, 1981; Bartnicki-Garcia & Lipmann, 1982; Bartnicki-Garcia, 1987; Fleet, 1991). On the other hand, we know much less about the other components of the wall. Enzymes are present (see Chapter 2) and polyphosphates can be present (see Chapter 7). Here I concentrate on what we know about the physicochemical properties of the wall of Saccharomyces cerevisiae and other yeasts, drawing attention afterwards to some salient features of the walls of other fungi.