Changes in fungi with age. II. Respiration and respiratory enzymes of Rhizoctonia solani and Sclerotium bataticola

Changes in ribonuclease with age in the fungus Rhizoctonia solani

The enzyme ribonuclease (RNase) which was isolated from Rhizoctonia solani Kuehn degraded ribonucleic acid from both Torula yeast and from Rhizoctonia solani mycelia. As the Rhizoctonia mycelia aged, there was an increase in both the total and the specific activities of the RNase present in the mycelia. This change is discussed in relation to the age dependent decrease in protein synthesis in this fungus.

Age-related changes associated with the induction of o-pyrocatechuic acid carboxylase in Aspergillus ornatus

Mycelial mats of Aspergillus ornatus grown on cellulose xanthate membranes placed on a defined agar medium showed o-pyrocatechuic acid carboxyalse activity which could be induced to over six times its basal level by the addition of 0.1% L-tryptophan to the medium. Exposure of mature mycelial mats to cyclohexamide prior to induction indicated that de novo protein synthesis was required for this induction to occur. The effect of age of this enzyme adaptation process was investigated by transferring membranes and mats of variuos ages from defined medium to fresh defined medium plus 0.1% L-tryptophan With increasing mycelial age, the basal enzyme activity level remained relatively unchanged while the level to which the enzyme could be induced decreased significantly. This decrease was linear when plotted against the mean cell age of mycelium, conforming to a general model of age-dependent modifications of the enzyme adaptation process proposed by Adelman. Several possible explanations of this phenomenon are discussed.

Oxygen consumption of Phycomyces sporangiophores

The respiration of stage-I,-III, and-IV sporangiophores of Phycomyces was measured. The [Formula: see text] of stages-I and-IV is low compared to that of actively growing mycelium. The [Formula: see text] of stage-III sporangiophores is somewhat higher than that of stages-I and-IV. As stage-I sporangiophores elongate their respiration rate increases proportionately. The respiration rate of stage-IV sporangiophores does not change as they elongate. In stage-IV sporangiophores the growing zone and the columella together consume as much oxygen as the rest of the sporangiophore does. Changes in the sporangiophore's growth rate have no effect on its oxygen consumption.

In vitro protein synthesis and aging in Rhizoctania solani

A study was made of the ability of cell-free protein synthesis systems from vegetative cells of different age of the fungus Rhizoctonia solani to produce polyphenylalanine. Polyuridylic acid-directed phenylalanine incorporation into peptides decreased linearly with cell age. The 105,000 x g supernatant fluid and ribosomal fractions were equally responsible for the total loss of synthetic activity of the older cells. Initial rates of phenylalanyl-transfer ribonucleic acid (tRNA) synthetase activity decreased with increasing cell age, which accounted for the defect of the supernatant fraction. An accelerated degradation of soluble phenylalanyl-RNA was associated with the ribosomes of the older cells. In vitro systems from cells of different age transferred phenylalanine from phenylalanyl-tRNA to polyphenylalanine at similar rates. Of the 15 specific aminoacyl-tRNA synthetases assayed, 5 increased and 5 decreased in specific activity with increased age; 3 others did not change during aging and 2 were below acceptable detectable levels.