Dynamics of sporangial emptying in Achlya intricata

Abstract

The dynamics of sporangial emptying in the zoosporic fungus Achlya intricata were characterized by analysis of photographic and video records of spore release. The mature sporangium is a semirigid cell wall enclosing loosely packed unicellular spores. There is a highly significant linear relationship between sporangial volume and the number of spores produced. During discharge, the spores exit the sporangium in a pulse-like fashion, the motion of the sporangial contents being punctuated by the passage of each successive spore through the constricting papilla. The plot of the number of spores released against time (“emptying profile”) is a rectangular hyperbola indicating that the velocity of spore release decreases during the emptying process. However, each individual spore accelerates during its passage through the sporangial lumen. Spore velocity shows a strong temperature dependence and is higher in larger sporangia than in smaller ones. Puncture at any point along the surface of the mature sporangium results in the release of spores through the artificial opening. Dynamically, sporangial emptying in A. intricata shares many features in common with Phytophthora cactorum and best fits a model based on the regulated dissipation of an osmotically generated pressure potential. This hypothesis is supported by mathematical modeling and the results of previous experiments.