Electron microscopy of barley root infection by the fungal pathogen Bipolaris sorokiniana

Abstract

An electron microscopic investigation of barley roots infected in vitro by Bipolaris sorokiniana showed the existence of an extracellular sheath on germ tubes and appressoria attached to the root surface. Growth of the fungus in the epidermis and outer cortex was predominantly intracellular, whereas in the inner cortex the hyphae observed were mainly intercellular. Hyphae could not be detected in the stele 24 or 72 h after inoculation. Enzymatic activity in the apex of penetration hyphae is a possible explanation of the electron-dense areas seen in host cell walls 72 h after inoculation. Separation of plasmalemma from cell wall and degeneration of host nuclei and mitochondria were other infection-induced changes commonly seen. A host response to fungal infection involved the development of papillae between the plasma membrane and cell wall of the plant as well as around fungal hyphae. Key words: Bipolaris sorokiniana, Cochliobolus sativus, Helminthosporium sativum, Hordeum vulgare, barley, root, microscopy.

Ultrastructure and composition of cell wall appositions in the roots of Asplenium (Polypodiales)

“…The small diameter of the hyphae and the absence of dolipore septa indicate that a basidiomycete is probably not responsible for the formation of CWAs. CWAs, similar to the ones studied here, have more frequently been described in association with plant-pathogenic Ascomycota such as Bipolaris (Carlson et al, 1991), Botrytis (Archer and Cole, 1986), Colletotrichum (Mims and Vaillancourt, 2002;Wharton et al, 2001), Erisyphe (Smith, 1900), Fusarium (Beswetherick and Bishop, 1993;Griffiths and Lim, 1964;Smith and Peterson, 1985), Leptosphaeria (Roussel et al, 1999), Gaeumannomyces (Yu et al, 2010), Ophiobolus (Fellows, 1928), Trichoderma (Yedidia et al, 1999), and Verticillium (Griffiths and Lim, 1964;Griffiths, 1970;Storey and Evans, 1987). In most cases, they penetrate plants by use of penetration pegs which are thin tip-growing cellular protuberances, generally less than 1 m in diameter (Howard, 1997).…”

Effect of the fungal pathogen Bipolaris sorokiniana toxin prehelminthosporol on barley root plasma membrane vesicles

“…deposition of electron-dense material between the cell wall and the plasma membrane has been observed ( Fig. 1; Carlson et at., 1991b), supporting the view that enzymes producing electron-dense material, which may seal leaky membranes, are active despite being locally exposed to toxin.…”

“…depending on the host tissue invaded. An electron microscopical investigation of barley roots infected by B. sorokiniana has shown that the fungal hyphae grow predominantly intercellularly in the cortex (Carlson et al, 1991b). Separation of the plasmalemma from the cell wall together with degeneration of host nuclei and organelles were changes commonly induced by infection, even in cells ahead of invading hyphae.…”

Seed-transmitted beneficial endophytic Stagonospora sp. can penetrate the walls of the root epidermis, but does not proliferate in the cortex, of Phragmites australis

“…Root pathogens such as Bipolaris sorokiniana can reach the endodermis of Triticum aestivum (wheat) or barley roots within 2-3 d (Carlson et al 1991). The wilt-inducing pathogenic F. oxysporum massively invades all tissues of Pisum sativum (pea) roots until it reaches the xylem.…”