Metamorphose-Induktion bei Planulalarven

Abstract

1. The metamorphosis of the planulae ofHydractinia echinata (Hydrozoa) is induced by certain marine, gramnegative bacteria which at the end of the exponential growth release a stimulating principle. 2. The stimulus is liberated by stationary cells previously cultivated at low population densities (up to 10 cells/ml) in a proper medium (e.g. extract of meat). Transfer into seawater lacking nutritive sources enhances the inductive capacity. 3. The concentration of the inducing agent normally surpasses the threshold level only in the close microenvironment of living cells. But when shocked by a drop in the osmotic pressure the bacteria discharge increased amounts which become traceable in the filtered cell-free medium. 4. Thus the inducer can be accumulated and isolated by a process of osmotic shock which does not affect the viability of the microbes. The principle belongs to a category of microbial substances which are subsumed under the comprehensive term "leakage"-products. 5. The active principle can be precipitated from the leakage solution with acetone and extracted with chloroform. The inducer seems to be an unstable, nondialyzable, polar lipid. 6. In order to evoke complete metamorphosis the isolated agent must be applied in a pulse-like fashion. Using the onset of metamorphosis as criterion for the velocity of reaction the dose-response curves display Michaelis-like saturation kinetics. At short pulses the percentages of induced metamorphoses yield a saturation curve as well. This indicates that an enzyme or carrier-system is involved in the larval response. 7. The inducing effect of the bacterial principle is antagonized by ouabain. Conversely, high doses of the isolated leakage material abolish the ouabain inhibition. The primary effect of the inducer, therefore, can be interpreted as stimulation of the active cation transport, especially of the Na/K-ATPase.

Protein kinase C in hydrozoans: involvement in metamorphosis of Hydractinia and in pattern formation of Hydra

“…Planula larvae are induced to metamorphose by contact with environmental bacteria (Mtiller 1969). The active compound appears to be an unknown lipid synthesized by the bacteria (Spindler and Mtiller 1972;Mtiller 1973;Leitz and Wagner 1993).…”

Inhibition of metamorphosis by RFamide neuropeptides in planula larvae of Hydractinia echinata

“…Fertilized eggs of this species undergo rapid cleavage divisions for about a day and develop into spindle-shaped planula larvae in about 3 days (Plickert et al 1988). The planulae metamorphose into adult polyps when they receive appropriate environmental stimuli (Müller 1973;Leitz 1998aLeitz , 1998b; also see Fig. 1).…”

“…Both LWamides and RFamides are stored in sensory neurons which are presumably used to monitor the environment. The bacterial inducer, Alteromonas espejiana, growing on hermit crab shells appears to serve as an environmental signal that stimulates LWamidecontaining neurons (Müller 1973;Leitz et al 1994). Other marine bacterial species may also have the capacity to trigger metamorphosis (Kroiher and Berking 1999).…”

“…In the natural environment, two agents are thought to play important roles. One is bacteria of the genus Alteromonas living on hermit crabs (Müller 1973;Leitz and Wagner 1993). The other is the LWamide neuropeptides stored in sensory neurons in planula larvae (Leitz et al 1994;Leitz and Lay 1995).…”

Ultrastructural Observations on the Larva of Loxosoma pectinaricola Franzén (Entoprocta, Loxosomatidae)

“…The hydroid Hydractinia echinata, a symbiont occurring on gastropod shells occupied by hermit crabs, was the single example of a symbiotic association suspected to induce metamorphosis listed by Burke. It is suggested that planula are induced to metamorphose by certain gram-negative bacteria and/or chemicals produced by the bacteria as a leakage product (Muller 1969(Muller , 1973. Vibrations produced by the hermit crab have also been suggested to induce metamorphosis in these planula (Muller et af.…”