The Ultrastructural Architecture of the Walls of Some Hyphal Fungi

Abstract

The appearance of the walls of apical and sub-apical regions of hyphae of predominantly 5 day cultures of Neurospora crassa, Schizophyllum commune and Phytophthora parasitica as seen with the electron microscope, employing shadowed or sectioned material, is illustrated and desCribed in detail. The appearance of untreated or control material in buffer is compared with that exposed to various single and sequential treatments with enzymes, including laminarinase, Pronase, cellulase and chitinase, as well as various chemical treatments.From these observations is inferred the co-axial distribution of polymers such as PI ,3-, PI ,6-glucans, glycoproteins, proteins, chitin and cellulose in the walls of each species. The distributions have both similarities and differences between the species. The significance of all these features for the growth, mechanical rigidity and integrity of a hypha is briefly discussed. I N T R O D U C T I O NThe growth of fungal hyphae is not well understood. One reason for this is that the molecular architecture of hyphal walls has not received sufficient attention. Chemical studies are beginning to reveal the complexity of hyphal wall components (e.g. review, Bartnicki-Garcia, I 968), while studies with enzymes have indicated that they are arranged in definite layers, e.g. in Neurospora crassa . Only a little information is available concerning wall structure as revealed by electron microscopy (e.g. review, Aronson, 1965) and this is either based mostly on residual shadowed material after drastic chemical treatments, or from thin sections which alone are not very informative.In this paper we describe the consequences of treating hyphae with enzymes, singly or successively, and then examining both shadow-cast and sectioned material with an electron microscope. The three species studied were selected because they differ in the chemistry of their cell walls, which was relatively well known from studies by other investigators. This new approach provides information on a comparative basis, concerning the distribution and arrangement of certain kinds of polymers within hyphal walls. M E T H O D SOrganisms. The organisms used were as follows : an ascornycete, Neurospora crassa, wild type, Emerson A from the Neurospora stock cultures; Schizophyllum commune, a basidiomycete, was isolated from damp plywood in Newcastle upon

Hyphal Wall Growth in Neurospora crassa and Geotrichum candidum

“…The chemistry of the secondary wall probably differs both qualitatively and quantitatively from that of the primary wall (Hunsley & Burnett, 1970). Support for these contentions and the hypothesis presented in Fig.…”

“…The chitin content of the inner layer of the 'mature' hyphal wall of N. crassa (Hunsley & Burnett, 1970) provides further evidence in support of the above hypothesis, since the tips of hyphae of N. crassa and other fungi are covered by a microfibrillar mesh of chitin (Hunsley & Burnett, 1970). The chemistry of the secondary wall probably differs both qualitatively and quantitatively from that of the primary wall (Hunsley & Burnett, 1970).…”

“…crassa similar to those we report. The observation that the inner layer of the 'mature' hyphal wall of N. crassa @re-sent results, and Hunsley & Burnett, 1970) has approximately the same thickness (about 50 nm) as the primary tip wall (Table I ) suggests that the former may be continuous with the latter (Fig. 8).…”

Conidiophore and Spore Development in Aspergillus nidulans

“…This can be interpreted in terms of the wall materials maturing from an initially plastic secretion with at least one component common to both layers; in young (24 h) hyphae of Neurospora cnzssa (Hunsley & Burnett, 1970) the substructure of the wall is similarly absent at the apex and develops subapically.…”

“…As permanganate is known to be a degradative agent (Bradbury &k Meek, 1960) the suggested comparison could be studied further by comparing untreated walls with thoce degraded with specific reagents such as used by Hunsley & Burnett (1970). Because in hyphae the plasmalemmasomes are non-specifically distributed there has been some doubt as to their function.…”