Iam Cruickshank

The isolation and partial characterization of monilicolin A, a polypeptide with phaseollin-inducing activity from Monilinia Fructicola

Abstract The isolation and partial characterization of a polypeptide (mol.wt. ca 8,000) designated as monilicolin A is reported from mycelium of Monilinia fructicola . Monilicolin A is a sulphur-containing, highly water soluble peptide with ca 65 amino acid residues. No evidence for the presence of non amino acid groups was obtained. Monilicolin A is active as a phytoalexin-inducing agent at very low concentrations (ED50 = 8 × 10−9 M). Its action appears to be specific for phaseollin-induction in as far as it has been assayed at present. It is neither phytotoxic nor fungitoxic. The use of monilicolin A in studies on the induction of phaseollin biosynthesis is briefly discussed.

The antifungal activity of pterocarpans towards Monilinia fructicola

Abstract The antifungal activity towards Monilinia fructicola of some naturally occurring pterocarpans and a number of related compounds obtained by substitution, degradation and partial synthesis has been examined. Compounds that were effective as antifungal agents had ED 50 values around 2 × 10 −5 M. A structure-activity relationship is proposed.

Phaseollin and phaseollidin relationships in infection-droplets on endocarp of Phaseolus vulgaris

Abstract The relationships between two lipophilic pterocarpanoid phytoalexins, phaseollin and phaseollidin, were studied. Concentrations of these two compounds in infection-droplets were influenced by host cultivar, fungal species and length of incubation phase. In most experiments with the host cultivar Red Kidney Selection W245, phaseollin was the major component. The addition of cycloheximide and several other metabolic inhibitors to conidial inoculum and to monilicolin A solutions markedly altered the normal phaseollin/phaseollidin relationship. Two newly observed phenolic compounds were detected in diffusate solutions and in extracts from in vitro studies. These compounds were isolated and shown to be C20H18O5 and C20H20O5 and appear to be fungal hydroxylation products of phaseollin and phaseollidin respectively. The dynamic nature of the relationships between phaseollin and phaseollidin and the importance of evaluating, in quantitative terms, both the chemical concentrations and the biological activity of individual antifungal compounds in multicomponent phytoalexin systems is discussed.

Phaseollin production by live bean endocarp

Abstract The effect of conidial suspensions of Monilinia fructicola, aqueous solutions of monilicolin A, a polypeptide extracted from this fungus and of aqueous solutions of mercuric chloride were studied in relation to cell damage and phaseollin formation in bean endocarp. All damage was assessed as membrane responses measured by the inability of treated cells to plasmolyse and take up vital stains. Tissue sections were examined also by electron microscopy. Phaseollin was formed in all treated tissues. Some isolated dark brown cells were observed along with many apparently normal cells in bean tissue inoculated with M. fructicola. All cells in the tissue treated with monilicolin A and mercuric chloride (5 × 10−5 m ) were apparently healthy and indistinguishable from cells in untreated endocarp. It is concluded that, while ecrobiosis may occur in a few isolated cells of bean endocarp inoculated with fungal spores, phaseollin formation is not causally linked with this phenomenon.

Environment and Sporulation in Phytopathogenic Fungi IV. The Effect of Light on the- Formation of Conidia of Peronospora Tabacina Adam

Using a leaf·disk technique, an analysis of the effect of light on the sporulation intensity of P. tabacina was carried out. The following points were demonstrated: (I) Under conditions of continuous light, sporulation of P. tabacina is sensitive to very low light intensities. ED5!1 for inhibition of sporulation was 16 ftvV cm- 2 for incandescent light (4 f,c.), and 0·58 p.W cm-2 for a monochromatic light source (469 mpo) in the region of maximum effectiveness. (2) Dark treatments induced sporulation under otherwise continuous light conditions. The response was directly proportional to the length of the exposure to darkness over the period 1·5-7 hr. (3) The time of day at which sporulation occurred could be modified by adjustment of the time of day at which darkness was initiated. (4) Within the visible spectrum, the region exerting maximal inhibition on sporulation occurred at 450-525 mJL.

Nitrogen nutrition and the net accumulation of medicarpin in infection-droplets on excised leaflets of white clover

Abstract Nutritional treatments in pot culture established a range of levels in nitrogen content of white clover corresponding to severe deficiency through to adequacy. Analysis for medicarpin and for leaflet area in relation to nitrogen indicated an inverse relationship in the former and a direct relationship in the latter. However, the two effects did not appear to be causally related to each other. The inverse relationship between medicarpin concentration and the well-known effect of nitrogen in increasing disease severity in many plant species is consistent with the concept that plant nutrition can potentially play a role in disease resistance through its effect on phytoalexin formation.

Solute fluxes in infection-droplets at the interface between conidia of Monilinia fructicola and pea endocarp☆

Abstract This paper describes early events following inoculation of pea endocarp with water-droplets containing conidia of Monilinia fructicola . These droplets trap materials diffusing from potential host cells and from germinating conidia. Analysis of solutes in infection-droplets was made relative to those in control water-droplets. Conidia of M. fructicola required exogenous sources of carbon and nitrogen for germination in vitro . The first germ tubes appeared after 3 h incubation in the germination medium. The first changes in pea × M. fructicola diffusates were observed after 2–3h, as an increase in concentrations of small nitrogen-containing compounds including amino acids. After 4–6h, protein began to accumulate and the pH dropped. In inoculated and control droplets, carbohydrate levels increased with time. However, after 18 h incubation the water-soluble macromolecular carbohydrate content of infection-droplets had been extensively reduced relative to the water-controls and the free monosaccharide composition of the diffusates changed; fructose and glucose disappeared and arabinose levels rose. The carbohydrate composition of the 18 h pea × M. fructicola infection-droplets was compared with those of two other fungal species and of diffusion-droplets for two abiotic elicitors of pisatin.