STIMULATION OF ASEXUAL REPRODUCTION OF PILOBOLUS BY MUCOR PLUMBEUS

Page , Robert M. (Stanford U., Calif.) Stimulation of asexual reproduction of Pilobolus by Mucor plumbeus. Amer. Jour. Bot. 46(8): 579–585. Illus. 1959.—The fact that a culture of Pilobolus kleinii which was contaminated with Mucor plumbeus produced far more sporangia than had ever been observed before on a synthetic medium suggested that M, plumbeus produced a substance which stimulated asexual reproduction in Pilobolus. When grown on a medium containing asparagine, sodium acetate, hemin, thiamine, and salts, P. kleinii consistently produced more trophocysts and sporangia when grown with M. plumbeus than when grown alone. Sterilized filtrate of culture medium in which M. plumbeus had grown also stimulated sporangium formation by P. kleinii. By the use of 2 types of 2-membered culture in which there was no liquid connection between the 2 fungi, it was shown that the stimulatory substance was volatile. In addition to being volatile at room temperature, the material was soluble in acid but not in alkali, and it gave a positive reaction with Nessler's reagent. Since (1) the material had some of the properties of ammonia, (2) the intensity of asexual reproduction in 2-membered cultures with absorbents was correlated with the distribution of ammonia, (3) M. plumbeus produced ammonia when grown on asparagine, aspartic acid, or NaNO₃, and (4) the effect of the substance could be imitated either with gaseous ammonia or with ammonium salts at appropriate concentrations, it seems highly probable that the substance produced by M. plumbeus which stimulates asexual reproduction of P. kleinii and some other species of Pilobolus is ammonia.