Summary
Populations ofPhytophthora palmivora zoospores induced to undergo synchronous differentiation by the addition of pectin showed an ordered sequence of surface changes. Within 10 seconds “blebs” and “microvilli” appeared on the cell and flagellar surfaces. These projections gave the zoospore a highly irregular and even convoluted surface for up to 30 seconds poststimulation. Between 30 and 40 seconds, pits appeared on the surface, which began to assume a smoother texture. Zoospores then rounded up and by 4 minutes had assumed an almost spherical form. At this time the surface became wrinkled as though shrinkage had occurred. Germ tubes could be seen emerging from almost all cells by 40 minutes, and as germ tubes enlarged, the cell surface became smooth again but with a fibrous texture. Many zoospores retained their flagella through to the germling stage.
When cells were stimulated in iso-osmotic rather than hypo-osmotic media, germ tubes in most cases emerged at or very near the site of flagellar attachment. Differentiation in iso-osmotic media showed the same sequence except that the cells did not assume the spherical shape normally characteristic of cysts and germlings differentiating under hypo-osmotic conditions.
Strontium-induced differentiation again followed the same general sequence as desribed above, although the cell surface was noticeably more convoluted and irregular prior to the stage of the formation of pits, and flagella were always shed between 40 seconds and 1 minute. Calcium addition up to 20 seconds after the initiation of differentiation with pectin prevented a high proportion of zoospores from encysting, the cells remained motile, and although the frequency of surface blebs and microvilli increased, pits did not appear.
These surface changes are consistent with those expected during stimulus-mediated secretion, and it appears that calcium is able to inhibit differentiation only before the secretory step (pit formation).
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Paktitis, S., Grant, B. & Lawrie, A. Surface changes inPhytophthora palmivora zoospores following induced differentiation. Protoplasma 135, 119–129 (1986). https://doi.org/10.1007/BF01277005
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DOI: https://doi.org/10.1007/BF01277005