The Production of Ethylene by Penicillium Digitatum

SUMMARY

P. digitatum does not require any specific nitrogen source to produce ethylene. If organic and inorganic nitrogen compounds allowed growth, ethylene was produced. No specific carbon source is necessary for ethylene production, for when a large number of organic compounds were substituted singly in the basal medium, the fungus produced ethylene.

A method was devised to avoid possible toxic effects of a compound on P. digitatum in order to study ethylene production when ethanol and various acids were added to the medium. Small amounts of the compounds were added at several intervals after growth had become established on small amounts of glucose, but after all the glucose had disappeared from the medium. A considerable amount of growth occurred on acetic and pyruvic acid compared to no growth when the acids were added at the start. Citric, malic, lactic and succinic acids allowed ethylene production whereas acetic, pyruvic and fumaric acids, and ethanol did not. Growth was poor on the latter compounds, but enough mycelium was formed to allow for production of ethylene based on the production of 2.5 ppm from 9 mg mycelium in 0.1 percent glucose medium. An exception was fumarie acid, which was not utilized by P. digitatum.

Low concentrations of ethanol vapor inhibited elongation of pea seedlings and also caused leaf burn. When the fungus was grown in the basal medium in stationary flasks, ethanol was produced in quantities which inhibited elongation of the epicotyls of etiolated pea seedlings.

The production of ethylene by P. digitatum follows a regular course under a variety of different cultural conditions. Small amounts are produced as the fungus begins active growth, and this is followed by a rise to a maximum with subsequent reduction. The maximum production of ethylene occurred just prior to or simultaneously with maximum mycelial production.

There does not appear to be any direct relationship between the amount of mycelium formed and the amount of ethylene produced.

The addition of vitamins to the basal medium is not required for ethylene production. However, their addition invokes earlier initial ethylene production. This is accompanied by an acceleration of the initial growth of the fungus.

The effect of shaking on ethylene production of P. digitatum was to cause variable production. In some cases complete inhibition of ethylene production was observed, and in other cases the duration of production and the amount of ethylene produced was reduced.

Ethylene was produced at both high and low residual pH values.