Localization of fragile areas in walls of resting spores of Polymyxa betae

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Abstract
In a previous paper we reported that the resting spores of Polymyxa betae observed with the scanning electron microscope appeared to undergo germination on one side only; however, it was not possible to ascertain whether this was the upper or lower area of the resting-spore wall. This paper reports a sonication study of purified sporosori of P. betae performed to determine if there are any fragile areas that may be involved in germination in the walls of mature resting spores. The sporosori were sonicated and observed with the scanning electron microscope. Of the damaged sporosori, 95% showed fractures distributed exclusively on the upper area of the resting spores. In addition, observations made directly on the sporosori present in the host cells showed that the upper area of the resting-spore wall is oriented preferentially towards the periphery of the root. The favorable position inside the host and the greater fragility of the upper area of the resting-spore wall support the hypothesis that the latter is a preferential area of germination.