Carbohydrate Metabolism of Salt-tolerant Fructan Grasses as Exemplified with Puccinellia peisonis

Summary The physiological role of carbohydrates, particularly of water-soluble fructose polymers (fructans), in metabolism was studied in Puccinellia peisonis, a salt-tolerant, caespitose grass growing at the banks of salty pools (“Lacken”) in the Seewinkel area (Burgenland, Austria). High resolution steric exclusion chromatography (SEC) made it possible to determine the molecular-weight distribution of the homologous fructan series and to quantify the individual components. The seasonal changes in the concentration of free monosaccharides, sucrose, oligo- and polyfructans (in 4 fractions with increasing molecular weight) and starch, which always occurred in small quantities, were studied in relation to the plant's phenology. Results showed that high-molecular fructans (with a degree of polymerization, DP of more than 18) mainly served as storage components, whereas fructose oligomers, similar to the raffinose series in many dicotyledonous species, provided resistance to freezing. Fructose and sucrose contributed much to the osmotic potential of the plant, which as most monocotyledonous species is highly efficient in excluding excess ions from the substrate. The resulting osmotic values, however, are too low to bridge dry periods in summer. In such cases decomposition of the water-soluble fructans may lead to a rapid increase of the osmotic potential. Moreover, the possible role of low molecular-weight fructans (with DP 7 to 10) as effectors of osmoregulation is discussed. The multiform functions of a polymeric series of simple carbohydrates may help to explain the success of Poaceae in growing on dry biotopes.