CUTICLES FROM CHONDRUS CRISPUS (RHODOPHYTA)1

Abstract

ABSTRACTA simple, nondestructive physical process was developed for routinely isolating the outermost layers from female, male, and sporophyte fronds of Chondrus crispus Stack‐house. Yields of pure cuticles from apical segments ranged from 0.74 to 2.35% on a dry weight basis after 5–7 d of culture. These undegraded cuticles were examined by electron microscopy (scanning and transmission electron microscopy), spectroscopy (infrared and X‐ray), and chemical means.Cuticles isolated from female or male fronds were characterized by parallel arrays of electron‐dense lamellae (typically 6–14) alternating with more electron‐transparent regions. The thickness and uniformity of these lamellae provide the physical basis for the iridescence characteristic of C. crispus fronds. Sporophyte fronds are not iridescent. This phenomenon may be explained by the fewer electron‐dense cuticular lamellae (usually three to seven) and the fact that these lamellae anastomose freely to form a thin cuticle with a highly irregular substructure. Elements detected by X‐ray analysis, in addition to carbon and oxygen, included Mg, Br, S, and Ca in both gametophyte and sporophyte cuticles. Major features of FTIR spectra of all cuticles were absorbances due to proteins. A strong band, indicative of sulfate ester, occurred near 1250 cm−1 in all cuticle preparations. Gametophyte, but not sporophyte, cuticles absorbed at 935, 846, and 800 cm−1 consistent with the presence of kappa and/or iota carrageenan. Amino acid analyses showed that sporophyte and gametophyte cuticles were generally similar in gross composition. All contained proline as the principal residue together with significant amounts of cysteine, methionine, and lysine. Protein contents calculated from these analyses ranged from 37.6 to 44.4% on a dry weight basis as compared to 51.5–56.7% calculated from total nitrogen values. Up to 75% of the cuticle mass was solubilized by sodium dodecyl sulfate‐β‐mercaptoethanol. Three similar migrating bands were seen in female and male cuticle extracts on sodium dodecyl sulfate–polyacrylamide gel electrophoresis; however, none of the three weaker bands from sporophyte cuticles comigrated with those from gametophytes. Chloroform‐methanol extraction removed < 3.3% of the cuticle mass, suggesting that lipids were minor components.