Spore Germination and Carbon Metabolism in Fusarium Solani. Ii. Endogenous Respiration in Relation to Germination

Abstract

Spore gcrmination and carbon netabolism in Fusarium solani. II. Endogenous respiration in relation to germination. Amer. Jour. Bot. 50 (8): 806-814. Illus. 1963.-Endogenous oxygen uptake by ungerminated macroconidia of Fusarium solani f. phaseoli is more than doubled by exogenous ammonium ion and is increased about 7-fold by germination. The respiratory quotient is halved by the provision of ammonia, which has essentially no effect on the endogenous formation of carbon dioxide. Stimulation by azide and 2, 4-dinitrophenol suggests that the supply of phosphate acceptors regulates the rate of endogenous respiration. Mcrcurials poison the endogenous respiration, cyanide accelerates it, and iodoacetatc, arsenite, fluoride, and chelating agents have little effect. Respiration is little affected by changes in pH, external phosphate, oxygen concentration, and spore density, within the limits tested. Spore lipid concentration is increased by cultivation in a high-glucose medium, but this variation in lipid content of spores does not affect the endogenous Qo" nor does a high lipid content abolish the requirement for exogenous carbon for germination. Lipid utilization during endogenous respiration accounts for 37% of the loss in dry weight; lipid is also utilized during germination, but such utilization amounts to only about 5% of the carbon requirement. Neither mannitol nor nitrogenous compounds are significant substrates of endogenous respiration. The oxidation of the exogenous substrates tested does not measurably affect the concomitant rate of endogenous respiration. It is proposed that endogenous respiration can contribute to the synthetic processes of spore germination, although quantitatively insufficient to support germination without exogenous carbon. It is also questioned whether the respiratory quotient is an adequate index of the substrate of endogenous respiration. 1

Endogenous Metabolism of Fungus Spores

“…In essentially all published reports of stimulation we have encountered (2,15,16,18), the 2-to 3-fold increases reported have been much less dramatic than those observed here. The only exceptions are the studies of Desser and Broda (4, 5) who used labeled Bacillus cereus spores to permit detection of extremely low rates of respiration.…”

“…Webb (22) has discussed this in general terms and has proposed a number of hypothetical mechanisms to account for the phenomenon. Slater (19) gives additional discussion relating to agents which stimulate metabolism through uncoupling oxidative phosphorylation, the mechanism proposed by most workers.In essentially all published reports of stimulation we have encountered (2,15,16,18), the 2-to 3-fold increases reported have been much less dramatic than those observed here. The only exceptions are the studies of Desser and Broda (4, 5) who used labeled Bacillus cereus spores to permit detection of extremely low rates of respiration.…”

Sugar Alcohols (Polyols) in Fungi and Green Plants

“…For example, in some spores, the endogenous mannitol level declines during the first few hours germination but the net fall is very small compared to the loss in dry weight (e.g. Cochrane et al, 1963, for the germination of spores of Fusarium solani). This is justifiably taken as strong evidence that mannitol is not the major respiratory substrate.…”

“…Cochrane et al (1963) stress the dangers inherent in this approach w hen they state: 'The key assumption in the use of R.O. as an indicator of the substrate of metabolism is that the substrate is fully oxidized; failure of this assumption vitiates the whole approach'.…”

The Metabolism of Triglycerides by Spores of Penicillium roqueforti

“…Germination has also been associated w i t h the decrease in fungal spore lipid which occurs during incubation (Farkas & Ledingham, 1959;Cochrane, Cochrane, Collins & Serafin, 1963;Jack, 1964). Lipids are a prominent constituent of several species of fungi (Allen, 1965) and the activation or synthesis of an esterolytic system and its subsequent attack upon the lipid of the spore coat may be related to the swelling and increase in permeability of fungal spores which precedes germination (Yanagita, 1957 ;Ekundayo & Carlisle, 1964).…”