Studies in our laboratory as well as others strongly suggest that salicylic acid (SA) plays an important signaling role in plant defense against pathogens. We have found that increases in endogenous SA levels correlates with both resistance of tobacco to infection with tobacco mosaic virus and induction of defense-related genes such as that encoding pathogenesis-related protein 1 (PR-1). Some of this newly synthesized SA was conjugated to glucose to form SA 3-glucoside. A cell wall-associated S-glucosidase activity that releases SA from this glucoside has been identified, suggesting that SA 83-glucoside serves as an inactive storage form of SA.

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The effect of acarbose on the intestinal metabolism of glucose was investigated using an in vitro perfused preparation of the isolated rat small intestine-pancreas. In preparations perfused without intraluminal sucrose administration, the total glucose recovered in the portal effluent and the portal values of lactate, pyruvate and alanine did not depend on whether or not acarbose [1.5 mg/kg body weight (b.w.)] was present in the intestinal lumen. The intestinal glucose and lactate contents were very low at the end of the experiment, and identical with or without acarbose. Insulin and glucagon concentrations remained constant during the whole perfusion period. After intraluminal administration of sucrose a clear increase in portal glucose concentration was observed, which was severely reduced by acarbose administration no changes in portal levels of lactate, pyruvate, alanine, insulin and glucagon were observed. The intestinal content of sucrose at the end of the study was significantly higher in the presence of acarbose (1.5 mg/kg b.w.), while the glucose concentration was low both with and without acarbose (0.20 +/- 0.08 vs 0.29 +/- 0.09 mmol/l respectively). These results suggest that acarbose does not influence the metabolic utilization of the glucose being translocated from the lumen.