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Summary Cultured material of Sphagnum magellanicum was analyzed for the content of starch, sucrose, glucose, fructose and soluble oligosaccharides. In the photosynthetically active parts of the Sphagnum plant, the capitula, starch and sucrose accumulate in the course of the 12 h light period and are subjected to degradation during the following 12 h dark period. Such diurnal fluctuations are not found for glucose, fructose and the oligosaccharides. Repeated exposure of the Sphagna to low night temperature, which induces the synthesis of red wall pigments (sphagnorubins) characteristically alters the fluctuations of the carbohydrate levels. Nightly degradation of starch and sucrose is reduced, whereas the production in the light is hardly influenced. Thus, the content of both compounds increases. Sucrose is subjected to enhanced turnover before sphagnorubin accumulation occurs. This is substantiated by the kinetics of radioactive sucrose labelled by a feeding of the mosses with 14C-glucose at the time of maximum sucrose concentration. Cold-treated mosses possess higher activities of glucose-6-phosphate dehydrogenase (G6P-DH, EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (6-PG-DH, EC 1.1.1.44) than the controls. This finding and the fluctuations of the sucrose pool are taken as criterion for the use of sugar precursors in the biosynthetic pathway. The flow of radioactivity of the other three sugars indicates that they are not degraded after an initial phase of accumulation. Oligosaccharides occur as phosphate esters and seem to be metabolically active compounds, since they are subjected to high turnover. The amount of starch deposited in the upper zone of the stems of the moss plants remains rather constant during repeated cold application. By contrast, the level of sucrose and oligosaccharides rises. |
