International Journal of Biological Macromolecules 27 (2000) 21–27 Studies on the skeletal cell wall of the cystocarpic stage of the red seaweed Iridaea undulosa B.  Part II. Fractionation of the cell wall and methylation analysis of the inner core-fibrillar polysaccharides Marı ´a L. Flores a , Carlos A. Stortz 1b , Alberto S. Cerezo b, * ,1 a Farmacognosia, Departamento de Farmacia, Facultad de Ciencias Naturales, Uniersidad Nacional de la Patagonia San Juan Bosco, Km. 4 -9000 Comodoro Riadaia, Chubut, Argentina b Departamento de Quı ´mica Orga ´nica -CIHIDECAR, Facultad de Ciencias Exactas y Naturales, Uniersidad de Buenos Aires, 1428 Buenos Aires, Argentina Received 25 March 1999; accepted 8 September 1999 Abstract In order to determine the structure of the fibrillar cell wall, the material isolated from cystocarpic thalli of the red seaweed Iridaea undulosa was fractionated using different media. While classical methods produced a scarce solubilization of material, the use of lithium salts in polar aprotic solvents (dimethylsulfoxide or N,N-dimethylacetamide), had successfully extracted higher amounts of material. The final residue from the Li + /DMSO extraction contains cellulose and a mannan, while that from the Li + /DMAc extraction contains only cellulose and traces of a galactan. Methylation analyses of both residues confirm the presence of those polysaccharides, and shows that the mannan is (1 4)-linked. Treatment with proteases suggests that the protein is efficiently shielded from digestion. All the extracts and residues contain major amounts of (glyco)proteins and/or proteins, in agreement with a previous suggestion that they are of major importance in the structure of the cell wall. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Cell wall; Fibrillar polysaccharides; Iridaea undulosa ; Rhodophyta www.elsevier.com/locate/ijbiomac 1. Introduction The skeletal cell wall of red seaweeds has received little attention and, although cellulose has been iden- tified in some species [2–4], and a -(1 4)-mannan in others [2], it remains mostly unexplored. Recently, a cell wall protein from the gametophytic stage of Por - phyra purpurea has been studied [5]. The cystocarpic stage of the red seaweed Iridaea undulosa Bory (a.k.a. Sarcothalia crispata (Bory) Leister [6,7]) biosynthesizes a system of water-soluble /- and /-carrageenans that have been extensively studied in our laboratory [8–12]. As an extension to the single chemical and histochemical study carried out on the skeletal cell wall of this seaweed [1], we report now the fractionation of this cell wall, the analyses of the soluble fractions and residues, and the methylation analysis of the fibrillar polysaccharides, in the inner core of the cell wall. 2. Materials and methods Collection and sorting of seaweeds, retrieval and general analysis of the skeletal cell walls (fraction RC) was carried out as reported previously [1]. 2.1. Analytical methods Most of the analytical techniques were carried out as reported [1]. Some of the extracts retrograded on stand-  For part I, see Ref. [1]. * Corresponding author. Tel./fax: +54-11-4576-3346. E-mail address: cerezo@qo.fcen.uba.ar (A.S. Cerezo) 1 Research Member of the National Research Council of Argentina (CONICET). 0141-8130/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0141-8130(99)00116-6