Irith Marbach

Permeability of Seed Coats to Water as Related to Drying Conditions and Metabolism of Phenolics

The seed coat of Pisum elatius is normally impermeable to water. When seeds are dried in the absence of oxygen their coats are totally permeable to water. Structural differences are observed between permeable and impermeable seed coats. In the genus Pisum, species with normally impermeable seed coats have a high content of phenolics and of catechol oxidase, while seed coats of P. sativum contain very little catechol oxidase and have a very low content of phenolics. Such differences are not noted in the cotyledons. We hypothesized that during dehydration of seeds, oxidation of phenolic compounds in seed coats through catalysis of catechol oxidase in presence of O(2) might render the seed coats impermeable to water.

Pectin, a second inducer for laccase production by Botrytis cinerea

Abstract Pectin acts as a second inducer of extracellular laccase formation by Botrytis cinerea , in the presence of a phenolic substance as a first inducer, but pectin alone fails to induce enzyme formation. The possible advantages of this mechanism for the fungus during the process of infection and overcoming host resistance are discussed.

Molecular properties of extracellular Botrytis cinerea laccase

Abstract Two molecular forms of extracellular laccase induced by different phenolics were studied in Botrytis cinerea . The enzyme induced by grapejuice had a MW of 38 000 and contained 80 % sugar while that induced by gallic acid had a MW of 36 000 and contained 70 % sugar. Both forms contained arabinose, xylose, mannose, galactose and glucose but differed markedly in the relative content of these sugars. Tunicamycin, which inhibits glycosylation of peptide chains, considerably reduced the level of laccase in both hyphae and medium. The two enzyme forms differed also in their isoelectric focusing pattern and amino acid composition, the grape juice enzyme being richer in basic amino acids and poorer in acidic ones. A third form, induced by p -coumaric acid, resembled the laccase induced by gallic acid in many of its properties but was apparently not identical to it. The possible significance of the various forms in relation to the infection process by the fungus is discussed.

Induction of laccase formation in Botrytis.

Abstract Optimal conditions for laccase excretion by Botrytis cinerea were determined. Addition of gallic acid to the culture medium induced maximal enzyme production and excretion. Other inducers previously reported for other organisms were ineffective. The relationships between internal and external laccase formation were determined.

Properties of gallic acid-induced extracellular laccase of Botrytis cinerea

Abstract The properties of the extracellular laccase produced by Botrytis cinerea induced by garlic acid are compared with the laccase produced by Botrytis in the presence of grape juice. The extra- and intracellular laccases are compared and found to be very similar.

Inducer and culture medium dependent properties of extracellular laccase from Botrytis cinerea

Abstract Both the composition of the culture medium and the nature of the phenolic inducer determine the amount, the rate of formation and the molecular properties of extracellular laccase formed by Botrytis cinerea . Coumaric acid is shown to act as inducer in addition to gallic acid and grape juice. It is suggested that the fungus adapts to different environments by excreting different laccases. These laccases differ in p K , heat stability and substrate specificity but not in K m values to quinol and oxygen.

Laccase in Anacardiaceae

Abstract The presence of a typical laccase is demonstrated in the cavities of the secretory ducts of a number of species of the Anacardiaceae, including Mangifera indica and Schinus molle . In addition mango fruit contains catechol oxidase. The presence of laccase may be of chemotaxonomic value.

Amino acid composition and molecular weight of Botrytis cinerea laccase

Abstract The extracellular laccase from Botrytis cinerea is shown to be a glycoprotein, of MW 56 000, containing at least one Cu atom/molecule. Its amino acid composition shows an exceptionally low content of basic amino acid and very high content of threonine and serine.

Galactosidases in cultivated and wild peas

Abstract The level of α- and β-galactosidase was followed in the cotyledons and embryos of germinating seeds of Pisum sativum and P. elatius . α-Galactosidase is preformed in the cotyledons but its activity increases during germination in the embryos. β-Galactosidase activity in embryos increases during germination but shows little change in cotyledons. The possible function of α- and β-galactosidase is discussed.

Lack of embryonic axis control in Pisum cotyledon mitochondria

Abstract Respiratory control ratio (RCR), ADP: O and oxygen uptake by isolated mitochondria from cotyledons of the genus Pisum were studied. It is shown that in P. sativum the embryonic axis has a slight effect on the behaviour of the mitochondria in the cotyledons, accelerating their degeneration. The inducing factor is transferred within 1 hr from the onset of imbibition from the axis to the cotyledon. In P. elatius the embryonic axis completely lacked an effect on the mitochondria in the cotyledons. Mitochondria in P. elatius seemed to be highly organized and not leaky.