The cell wall composition of several species of the lichen phycobionts Trebouxia and Pseudotrebouxia has been investigated using gas chromatography, thin layer chromatography and infrared absorption spectrophotometry. In addition cell wall components (cellulose, non-cellulosic polysaccharides, sporopollenin, protein) were localized with cytochemical methods at the EM- level. The cell walls of Trebouxia and Pseudotrebouxia consist of several layers. In Trebouxia the inner layer (Si) consists mainly of cellulose, then followed by a non-cellulosic polysaccharide layer (S2), a sporopollenin-layer (S3) and an outer layer consisting again of a non-cellulosic polysaccharide (S4). In addition Trebouxia is surrounded by a sheath (a polysaccharide with species-specific terminal residues). In Pseudotrebouxia the cell wall is similarly constructed compared to Trebouxia, however, the sheath is lacking and the S4 layer contains a polysaccharide with species-specific terminal sugar residues. The role of the different cell wall constituents for the recognition mechanism between the lichen symbionts is discussed.
SUMMARYThe ultrastructure of the phycobiont, Coccomyxa, was compared in some asco-and basidiolichens. All phycobionts investigated contained a single cup-shaped chloroplast, multivesicular bodies and large storage bodies. In the chloroplast of the phycobionts in ascolichens, many plastoglobuli occurred regularly whereas, in those of the basidiolichens, no plastoglobuli were present. The multivesicular bodies were associated with varying numbers of vesicles and storage bodies. The storage bodies increased when the lichens were kept dry for several months. By cytochemical tests, the lipid nature of these bodies was suggested. The possible function of the different structures is discussed in comparison with the ultrastructure of other lichens.
The occurence and size of plastoglobuli were studied in the different types of plastids from Allium cepa. The function of plastoglobuli as a reservoir for lipoquinones is discussed. 1. The white turgescent leaves of the onion contain chloroplasts in the cells close to the vascular bundles. These chloroplasts show the usual thylakoid arrangement and possess numerous plastoglobuli (av. diameter 65 nm). There also exist plastid-like components with concentrically arranged membranes and osmiophilic lipid inclusions (av. diameter 200 nm). 2. The chloroplasts in green sprouting leaves contain less and smaller plastoglobuli (diameter ca. 45 nm). 3. The plastoglobuli from leucoplasts possess the same size as plastoglobuli from chloroplasts in the onion leaves. The leucoplasts of the epidermis cells contain, however, less plastoglobuli than leucoplasts of the onion mesophyll. 4. The lipoquinone content in chloroplasts from green parts of the white turgescent onion leaves is much higher than in chloroplasts from green sprouting leaves. The concentrations of plastoquinone 45 are 25 X, of \ga-tocopherol 21 X, of \ga-tocoquinone 3,7 X and of vitamin K1 2,5 X higher with reference to chlorophyll a. 5. There is a direct correlation between lipoquinone and plastoglobuli content of plastids.
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