A new method for the rapid and quantitative fluorometric determination of callose is described. In suspension-cultured cells of Glycine max, synthesis of callose starts within 20 minutes of treatment with chitosan and parallels over hours the accumulation of 1,3-linked glucose in the wall. Poly-L-lysine also elicits callose synthesis. The effect of chitosan is enhanced by Polymyxin B at low concentrations; this antibiotic alone at higher concentrations can also induce callose synthesis. Callose synthesis is immediately stopped when external Ca2l is bound by ethylene glycolbis-(2-aminoethyl ether)-N,N'-tetraacetate or cation exchange beads, and partly recovers upon restoration of 15 micromolar Ca21.Callose synthesis is observed only when membrane perturbation causing electrolyte leakage from the cells is induced by one of the above treatments. It does not appear to be due to de novo synthesis or proteolytic activation of 1,3-#-D-glucan synthase. It is concluded that this Ca24-dependent enzyme is directly activated by the influx of Ca24 occurring concomitantly with the leakage of cell constituents. This suggestion is also discussed in conjunction with the chitosan-induced synthesis of phytoalexin in the same cells.

Although the apple extract substantially decreased intestinal glucose absorption in all test systems, the finding that there are systemic effects that relate to inhibition of glucose transport processes beyond the intestine addresses safety issues that need further exploitation.

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Due to the important physiological role of the complement system, complement modulation, either inhibition or stimulation, is an interesting target for drug development. Several plant polysaccharides are known to exhibit complement modulating activities. Sometimes these effects are described as complement inhibition, although the basic mechanism is a stimulation of the complement activation. This misinterpretation is due to the observed reduced haemolysis in the widely used haemolytic complement assay, which does not allow to differentiate between complement activators and inhibitors, when it is performed in the classical manner. The aim of the presented study was to demonstrate that by simple modifications of the classical procedure this assay becomes an efficient tool to distinguish between real complement inhibitors and complement activating compounds without performing expensive, molecular mechanistic investigations. As practical examples heparin with proven complement inhibiting activity and AGP, a new arabinogalacatan-protein type II isolated from pressed juice of the aerial parts of Echinacea purpurea, as a potential complement activating compound were included in the study. By means of varying the preincubation time of the test compound with complement, AGP was clearly identified as a stimulator of both the classical and alternative pathway of complement activation. These findings correspond to the results of molecular mechanistic investigations. Selective removal of the arabinose side chains of AGP resulted in considerably reduced activity. Therefore, the three-dimensional structure of the polysaccharide, i. e., a backbone branched by side chains, is supposed to be important for the interactions with the complement system. The complement activating effects of AGP may contribute to the well-established immunostimulating effects of the pressed juice from Echinacea purpurea. Abbreviations. AGP:arabinogalactan-protein AGP-hydr.:hydrolysed arabinogalactan-protein AP-CA:haemolytic complement assay for the alternative pathway CP-CA:haemolytic complement assay for the classical pathway EGTA-VB:veronal buffered saline containing EGTA and Mg 2+HPS:human pooled serum RT:room temperature LPS:lipopolysaccharide RaE:rabbit erythrocytes RT:room temperature ShE(A):(sensitised) sheep erythrocytes VB:veronal buffered saline containing Ca 2+ and Mg 2+

Glucose homeostasis is maintained by antagonistic hormones such as insulin and glucagon as well as by regulation of glucose absorption, gluconeogenesis, biosynthesis and mobilization of glycogen, glucose consumption in all tissues and glomerular filtration, and reabsorption of glucose in the kidneys. Glucose enters or leaves cells mainly with the help of two membrane integrated transporters belonging either to the family of facilitative glucose transporters (GLUTs) or to the family of sodium glucose cotransporters (SGLTs). The intestinal glucose absorption by endothelial cells is managed by SGLT1, the transfer from them to the blood by GLUT2. In the kidney SGLT2 and SGLT1 are responsible for reabsorption of filtered glucose from the primary urine, and GLUT2 and GLUT1 enable the transport of glucose from epithelial cells back into the blood stream.The flavonoid phlorizin was isolated from the bark of apple trees and shown to cause glucosuria. Phlorizin is an inhibitor of SGLT1 and SGLT2. With phlorizin as lead compound, specific inhibitors of SGLT2 were developed in the last decade and some of them have been approved for treatment mainly of type 2 diabetes. Inhibition of SGLT2 eliminates excess glucose via the urine. In recent times, the dual SGLT1/SGLT2 inhibitory activity of phlorizin has served as a model for the development and testing of new drugs exhibiting both activities.Besides phlorizin, also some other flavonoids and especially flavonoid enriched plant extracts have been investigated for their potency to reduce postprandial blood glucose levels which can be helpful in the prevention and supplementary treatment especially of type 2 diabetes.