RESPIRATORY BLOCK IN THE DORMANT SPORES OF NEUROSPORA TETRASPERMA

Abstract

Shear and Dodge (26) have shown that the ascospores of Neurospora tetrasperma are dormant, but that they may be induced to germinate by a short period of heating. This process of heat activation was studied by Goddard (7), who found that heating the dormant spores to temperatures of over 50? C. for a few minutes induced germination two to three hours after returning them to room temperature. Further, he found that the activation is reversible. If the respiration of the activated spores was prevented for several hours by anaerobic conditions or the addition of cyanide, upon returning to conditions favorable for respiration, the spores failed to germinate; that is, they had been de-activated. If the de-activated spores were re-activated by a second heat treatment, they germinated normally. The activation of the spores induced a large increase in the respiratory rate (8 to 40 times), and this high rate of respiration had to continue for two to three hours if germination was to occur. Upon germination, a second increase in the respiratory rate was found, nearly doubling that of the activated spores. Thus, he recognized three phases in the rate of respiration of the ascospores: (1) that of dormant spores, (2) that of activated spores (one-half hour to two hours after the heat treatment), and (3) that of germinating spores (the spores in which germ tubes may be seen under the microscope). In this paper we have tried to determine what constitutes the respiratory block of dormant ascospores of Neurospora tetrasperma, or, conversely, what part of the respiratory mechanism undergoes heat activation. It is to be realized that activation and germination occur readily in distilled water, so that an external substrate is not essential for activation or germination. We may assume concerning the respiratory systems of dormant and activated spores, either (a) that the dormant and activated respiratory mechanisms are qualitatively dissimilar or even independent, and that heat treatment causes a de novo appearance of a system inactive in dormant spores, or (b) that the same mechanism is functional in dormant and activated spores, but that in dormant spores the rate is limited by the slowest process in the total reaction chain, and that this slow reaction is greatly accelerated by the heat treatment, allowing the total respiratory chain to proceed at the rate found in activated spores. If the first assumption is correct, the respiratory block is the inactivity of the reaction which prevents the second 241