Wm. Goldberg et Gt. Taylor, COELENTERATE CNIDAE CAPSULES - DISULFIDE LINKAGES REVEALED BY SILVER CYTOCHEMISTRY AND THEIR DIFFERENTIAL RESPONSES TO THIOL REAGENTS, The Biological bulletin, 192(1), 1997, pp. 1-16
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.