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Ca2+-ions and pattern control in Hydra.

The fresh water polyp Hydraforms buds which develop a foot at their base and separate from the parent. In the strain H. vulgaris (Zürich), various compounds including phorbolesters, diacylglycerols, cantharidin and Li+-ions were found to prevent foot formation at the bud's base. Therewith, the bud transforms into a branch which persists at the parent. Other strains were found to be unaffected by such treatments. Here we show that a reduced Ca2+-ion concentration of the culture medium causes branch formation in the H. vulgaris (Zürich) strain but not in the other strains tested. However, all strains tested transformed their buds into branches when the medium was enriched with Ba2+ and Sr2+ ions. We suggest that the various treatments either reduce the internal concentration of Ca2+-ions by stimulating Ca2+-ion export or compete with Ca2+-ions at theirtarget. H. vulgaris (Zürich) isthe most sensitive strain tested and appears to have the most efficient Ca2+-pumps. This appears to be necessary forthese animals derived from a lake which is extremely rich in Ca2+ ions.