Biochemical interactions of conifer seedling roots with Fusarium spp.

Abstract

The importance of root and spore surface molecules in the interactions of Fusarium spp. with conifer roots, and cellular localization of proteins presumed to be involved in host defence, were investigated. For adhesion studies, using a combination of fluorescein isothiocyanate (FITC) labelled lectins and high perfomance liquid chromatography (HPLC), several sugars (pinitol, xylitol, galactose, mannose, and glucose) were detected in root surface mucilage. Both artificial substrata and detached living roots were used to evaluate the significance of selective removal of root or spore surface components on the adhesion process. The spores or roots were pretreated with either periodic acid, pronase E, potassium hydroxide or diethyl ether. Pretreatment of the spores with diethyl ether reduced significantly the level of spore adhesion, which suggests that the adhesive component is either a lipid, or is bound to lipid. Since oxidation of carbohydrate reactive sites with periodic acid on the root surface almost completely abolished the development of germ tubes by adherent spores, it was presumed that some of these periodate-sensitive substances serve as a nutrient source for the fungus. On inoculated roots, F. avenaceum and F. culmorum were significantly pathogenic to both Norway spruce and Scots pine seedlings. Cytochemical labelling of sites of accumulation of host defence molecules within infected root tissues using anti-peroxidase demonstrated increased peroxidase activity in host cell walls. With anti-chitinase and anti-glucanase, gold labelling was found mainly on pathogen hyphal walls.Key words: conifer seedlings, adhesion, Fusarium spp., PR proteins, immunolocalization, lectins.

Root Defense Responses to Fungal Pathogens: A Molecular Perspective

“…For example, a PR-10-like protein is expressed in the root hairs and root epidermal cells of pea plants (Mylona et al, 1994), and is postulated to have a defense function in these tissues. Hostderived chitinase and glucanase accumulate around hyphae of Fusarium culmorum and Fusarium avenaceum that infect roots of susceptible spruce and pine (Asiegbu et al, 1999). Hostderived chitinase and glucanase accumulate around hyphae of Fusarium culmorum and Fusarium avenaceum that infect roots of susceptible spruce and pine (Asiegbu et al, 1999).…”

Adhesion and development of the root rot fungus (Heterobasidion annosum) on conifer tissues: effects of spore and host surface constituents

“…Results were calculated as Wg ml 31 of sugars. Analyses of soluble sugars for root samples were the same as previously described [14].…”

“…¢ne and coarse roots). As a pre-requisite for establishment of root diseases in conifers [13,14], the host tissues and fungal material must come in contact at their cell surfaces. There is evidence that mucilage or polysaccharides may function in adhesion of fungal materials to host surfaces [15,16].…”

Levinas and Political Theory

“…The peroxidases constitute another important group of enzymes associated with phenolic chemistry that are involved in defense-related processes such as lignification, cross-linking of cell wall proteins, auxin catabolism, production of oxygen radicals, as well as direct defense against pathogens (Campa 1991, Mohan et al 1993, Otter and Polle 1997. Increased accumulation of peroxidases has been reported in Norway spruce seedlings infected with a root pathogenic fungus (Asiegbu et al 1999, Fossdal et al 2001.…”