COELENTERATE CNIDAE CAPSULES - DISULFIDE LINKAGES REVEALED BY SILVER CYTOCHEMISTRY AND THEIR DIFFERENTIAL RESPONSES TO THIOL REAGENTS

The sulfur cytochemistry of cnidae from the Portuguese man-of-war Phys alia physalis, the scyphozoan Cassiopeia xamachana, and the black cora l Cirrhipathes leutkeni was evaluated on the basis of electron microsc opy, X-ray microanalysis, amino acid analysis, and response to disulfi de reducing agents. The cnidae examined included large and small holot richous isorhizas in P. physalis, another small isorhiza in C. xamacha na, and both spirocysts and microbasic mastigophore nematocysts in C. leutkeni. A strong reaction with methenamine-silver reagent was charac teristic of all cnidae capsules, but the pattern and extent of that ar gentophilia was dependent upon the type of cnida and its state of matu rity. The large isorhizas of P. physalis reacted primarily in the oute rmost capsule layers, but in C. xamachana isorhizas, silver stained th e entire capsule with the exception of the outermost region. The small isorhizas of P. physalis and the mastigophore capsules of C. leutkeni stained throughout, whereas the spirocyst capsules were outlined by s ilver, clearly delineating the inner and outer lavers. All of these re actions were abolished with alkylation, but only after treatment with disulfide reducing agents; alkylation alone diminished silver staining only slightly, indicating that the argentophilic response was due pri marily to disulfide linkages. The cystine content of these cnidae vari ed from 4. 1 to 4.7 mole percent for a given species, but amino acid a nalyses did not separate components of the cnidom. Cnidae, both within and among species, exhibited differential responses to the disulfide reducing agent dithiothreitol (DTT). Isolated, unfixed, large isorhiza s of P. physalis discharged and appeared to dissolve rapidly in the pr esence of this reagent, whereas small isorhizas from both P. physalis and C. xamachana discharged, but dissolved slowly if at all. The disch arge and solution responses of the capsule coincided with the complete development of the tubule. Cnidae containing an undeveloped or partia lly developed tubule were resistant to DTT, displayed a weak capsular argentophilia, and contained background levels of sulfur; these result s suggest that formation of disulfide linkages is one of the final ste ps in capsular maturation. In contrast, mature nematocyst and spirocys t capsules in C. leutkeni tentacles were resistant to DTT among other reagents, despite the presence of disulfides. This suggests that other types of covalent, intermolecular linkages could play a prominent rol e in the development of capsular stability in this species.