Ca(2+)-dependent polarization of axis establishment in the tip-growing organism, Saprolegnia ferax, by gradients of the ionophore A23187.
A gradient of the divalent cation ionophore A23187 polarized axis establishment in regenerating hyphal protoplasts and germinating cysts of the tip-growing oomycete Saprolegnia ferax. An average of sixty-three percent of new hyphae emerging from initially spherical protoplasts were oriented towards the ionophore source. This polarization was dependent on the presence of Ca2+ and could not be elicited by the presence of either 1 mM Mn2+ or Mg2+. A similar but less marked (56%) orientation was shown by germinating cysts, either with or without pretreatment with the anti-microtubule drug, nocodazole. Further, cyst-derived hyphae which did not originally emerge facing the ionophore source later showed a tendency to reorient their growth towards it. Since A23187 is known to facilitate the entry of Ca2+ into cells, and since, in protoplasts at least, the response is Ca2+ dependent, these results imply that an ionophore-generated Ca2+ gradient within the cells may be responsible for the observed polarizing influence on protoplasts and cysts. It is likely that the role of Ca2+ is essentially the same in both systems: a primary common factor in the establishment of the growth axis. The results provide evidence that Ca2+ polarizes hyphal growth and support the idea that Ca2+ has a ubiquitous, primary role in the initiation of polarity in tip-growing cells.[1]References
- Ca(2+)-dependent polarization of axis establishment in the tip-growing organism, Saprolegnia ferax, by gradients of the ionophore A23187. Hyde, G.J., Heath, I.B. Eur. J. Cell Biol. (1995) [Pubmed]
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