Environmental Parameters Limiting Spore Germination in a Spontaneously Germinating Mutant of Dictyostelium Discoideum

ABSTRACT

Mutant strain SG1 spores of Dictyostelium discoideum spontaneously germinate in the absence of an external stimulant. Like externally activated wild-type NC4 spores, mutant SG1 spores did not germinate to high percentages under harsh environmental conditions. Upon release from these harsh conditions, unlike the wild-type spores, the mutant spores germinated normally without any added external activation treatment.

Addition of crude autoactivator to mutant spore suspensions extended the germination boundaries of certain environmental parameters beyond those boundaries observed for unstimulated spores. For example, autoactivator-stimulated SG1 spores germinated at higher temperatures, at higher and lower pH, under high osmotic pressure, and to a limit, under reduced oxygen concentrations when compared to unstimulated SG1 spores. Unlike the wild-type strain, naturally germinating SG1 spores did not exhibit a deactivation mechanism. In general, harsh environmental conditions blocked either production or secretion of the autoactivator but only marginally interfered with the response of spores to the presence of exogenous autoactivator. The presence of light did not enhance either the production of autoactivator or the response of spores to exogenous autoactivator.

A comparison between the process of spore autoactivation and cellular aggregation is discussed.

Key Words:

• Dictyostelium discoideum
• spore
• germination
• autoactivator