The cell wall galactans from Australian representatives of the genus Meristotheca (Solieriaceae, Rhodophyta)

Abstract

The Solieriaceae has the largest number of genera (16–18) of any family in the carrageenophyte order Gigartinales. One of these genera, Meristotheca, consists of three or four species of foliose, erect to prostrate plants sporadically recorded from the tropics of both hemispheres. The hot-water-soluble polysaccharides from Australian representatives of the type species, M. papulosa, and M. procumbens from Lord Howe Island have been characterized by compositional assays, linkage analysis, and Fourier transform infrared and 13C-nuclear magnetic resonance spectroscopy. The results show that polysaccharides from both species are similar, being predominantly composed of 4-linked 3,6-anhydro-α-D-galactopyranose 2-sulphate alternating with 3-linked β-D-galactopyranose 4-sulphate, as is typical of ι-carrageenan. Small proportions of the 3-linked units occur as the pyruvated residue 4,6-O-(l-carboxyethylidene)-β-D-galactopyranose, and other minor variations from idealized ι-carrageenan were also detected. The polysaccharides from representatives of Meristotheca are comparable to those of other solieriacean algae analysed to date, but the minor structural variations suggest a closer chemotaxonomic affinity with noneucheumoid genera of the Solieriaceae, such as Sarconema, Solieria, and Tikvahiella, than to the eucheumoid genera Eucheuma, Kappaphycus and Betaphycus (tribe Eucheumatoideae) from which most κ- and ι-carrageenans are commercially extracted.