Polyphenol oxidases in plants

Factors regulating production of glucose oxidase by Aspergillus niger

Characteristics of phosphate solubilization by an isolate of a tropical Penicillium rugulosum and two UV-induced mutants

Internationally collected data concerned with variation for pathogenicity in Plasmodiophora brassicae and for clubroot resistance in three Brassica species, together with additional experimental evidence, were used to elucidate the major genetic features of this host-parasite relationship. The major components of resistance in B. campestris and B. napus were differential and xobahly oligogenic. Good agreement was found between the data and simple gene-for-gene schemes. In contrast, the major component of resistance in most B. oleracea genotypes appeared to be non-differential and there was evidence of pathogen variability for non-differential pathogenicity. A strong association between pathogenicity on any resistant B. campestris genotype and on all resistant B. napus genotypes was apparent, suggesting the possibility of genes in common. There was evidence that P. brassicae collections carrying certain characters for differential pathogenicity on these two species were less pathogenic on B. oleracea. However, there was no ether evidence of pathogenic specialization to a particular host species. Several analytical procedures were employed which may prove useful in clarifying the important features of other host-parasite combinations.

The relationship between genotypes of three Brassica species and collections oi Plasmodiophora brassicae

Spore morphologies are a major character in fungal taxonomy, although many isolates are not able to sporulate on common artificial media. This article reviews the effect of nutrition, host tissue, and light on fungal sporulation in artificial media. A trial experiment using 42 strains that failed to sporulate on potato dextrose agar (PDA) and half-strength PDA after 3 months is reported. Five strategies (1/10-strength PDA, CaCO3 water agar, pine needle medium, mulberry agar, and near-ultraviolet light irradiation) were applied to induce these strains to sporulate, with an overall success rate of 62%. Pine needle medium was the most successful method, which induced sporulation of 40% of recalcitrant strains.

Induction of sporulation in plant pathogenic fungi

Submerged cultures of Penicillium notatum on a modified Czapek-Dox medium, containing sucrose or glucose, were characterized by high intracellular and extracellular glucose oxidase activity, heavy gluconate production and failure to sporulate. Addition of Ca 2+ to cultures within 48 h of inoculation promoted sporulation, greatly reduced the rate of increase of glucose oxidase activity in the biomass and medium and, in turn, the production of extracellular gluconate. Gluconate media supported slow growth of the fungus and a low level of sporulatiom even in the absence of Ca 2+ but the addition of Ca 2+ enhanced spore formation. Fructose media, on which glucose oxidase and gluconate were not produced, supported Ca 2+ -induced sporulation which was, as with sucrose and glucose, entirely dependent upon the presence of Ca 2+ within 48 h of inoculation; thereafter the Ca 2+ effect was not manifested. The possible role of gluconate as a regulator of sporulation is discussed, along with views that ageing of components of the biomass may exert a primary effect upon the sites of the Ca 2+ trigger.

Glucose oxidase activity and gluconate production during calcium-induced conidiation of Penicillium notatum in submerged culture

Uptake of calcium ions by Penicillium cyclopium in submerged culture was biphasic. The ion underwent rapid initial binding to the mycelium with a dissociation constant (KD) value of 0.114 mM-Ca2+ and binding capacity (Yt) of 3.5 nmol-Ca2+ (mg dry wt)−1. Metabolismindependent chemical adsorption of calcium was followed by metabolism-dependent active transport with a Km value of 1.88 m m and Vmax of 8.9 nmol-Ca2+ (mg dry wt)−1 min−1. Time-course experiments showed that exposures of mycelium to Ca2+ for periods as brief as 30 s were accompanied by substantial Ca2+ binding, but negligible active transport of the ion, and resulted in conidiation identical to that in cultures continuously exposed to Ca2+. The relationships between calcium binding and the mechanisms of conidiation in P. cyclopium are discussed.

Calcium uptake kinetics in relation to conidiation in submerged cultures of Penicillium cyclopium

Intracellular sites of binding or accumulation of calcium ions, which are essential for induction of submerged conidiation in P. cyclopium, were determined by assay of 45Ca in organelle fractions derived from mycelium which had previously been incubated with 45Ca. The radionuclide was found principally in fractions rich in plasma membrane components and in intact mitochondria. Electron microscope autoradiography using 45Ca was done using a modified fixation procedure which, by avoiding osmication, prevented extensive leaching of the isotope from the wall. Autoradiographs provided further evidence of calcium binding to the tonoplast in addition to its associations with the plasma membrane and the mitochondria. The physiological implications of the accumulation of calcium at subcellular sites are discussed with special reference to membrane binding and its relationship to conidiation.

Subcellular sites of calcium accumulation and relationships with conidiation in Penicillium cyclopium

Enzyme extracts from healthy potato tuber tissues and tissue culture cells showed varying phosphohydrolytic activity towards a range of phosphate esters. Infection of tissues by Phytophthora erythroseptica Pethyhr. resulted in increased acid phosphatase activity towards some substrates and decreased activity towards others. Changes in several carboxylic esterase activities occurred following tissue infections. Disk electrophoresis of enzyme extracts on Polyacrylamide gel, using α-naphthyl esters as substrates, indicated the existence of multiple forms of acid phosphatase and carboxylic esterases in both healthy and infected tissues.

Changes in hydrolase activity of Solanum tuber tissues during infection by Phytophthora erythroseptica

Penicillium notatum IMI 15378 sporulated profusely in submerged culture containing 10 mM-Ca 2+ , whilst the response of strain NRRL 832 was minimal up to 40 m m concentration of the cation. Calcium accumulation by mycelia of both strains was biphasic and involved rapid initial energy-independent binding, with the strains showing similar affinities for the cation, but with the responsive strain having a binding capacity four times greater than the nonresponsive strain. The second phase of Ca 2+ uptake was energy-dependent, involved ATPase activity, and showed saturation kinetics with K m values of 0.28 and 0.42 m m -Ca 2+ and V max values of 0.6 and 0.15 nmol (mg dry wt) −1 min −1 , for strains IMI 15378 and NRRL 832 respectively. Metabolically active preparations of protoplasts were free from wall contamination, and showed similar Ca 2+ binding affinities but these were lower than in the equivalent mycelia. The binding capacity of strain IMI 15378 was an order of magnitude greater than that of strain NRRL 832. Energy-dependent calcium transport was only demonstrated in strain IMI 15378 and followed saturation kinetics with a relatively low maximum influx rate. Isolated cell walls of both strains showed Ca 2+ binding characteristics similar to those of the respective mycelia.

D. Pitt

Papers

Glucose oxidase activity and gluconate production during calcium-induced conidiation of Penicillium notatum in submerged culture

Calcium uptake kinetics in relation to conidiation in submerged cultures of Penicillium cyclopium

Subcellular sites of calcium accumulation and relationships with conidiation in Penicillium cyclopium

Changes in hydrolase activity of Solanum tuber tissues during infection by Phytophthora erythroseptica

Differential uptake of calcium by strains of Penicillium notatum and relationships to calcium-induced conidiation