Technics of Plant Histochemistry and Virology

Abstract

452 nose, xylose, rhamnose, galactose and uronic acid (table 2). These latter sugars were not detected in the monomeric form nor as components of the lower MW oligosaccharides (table 1, mono-to tetrasaccharides). Pmification of the largest oligosac-charities (MW i> 2200 D) by anion exchange chromatography revealed that the oligosaccharides in the unbound fraction (~ 0.5% of total honeydew carbohydrate) were oligoglucans similar to those found in the honeydew of aphids fed on artificial diets containing only sucrose ~ and, hence, were polymerized by the aphid. Conversely, the oligosaccharides in the acid fraction (1.8% of total honeydew carbohydrate) were polymers consisting chiefly of arabinose, galactose, and uronic acid, with significantly less glucose than those oligosaccharides in the un-bound fraction (table 2). Furthermore, the neutral sugar and uronic acid composition of these acidic oligosaccharides was qualitatively similar to pectic substances extracted from the same host plant, sorghum variety 'BOK-8' (table 2). Greenbugs cannot synthesize polyuronides or pentans, thus, the acidic oli-gosaccharides in their honeydew appeared to be of plant origin. To test whether the pectic fragments could have originated in the phloem, cross sections of sorghum leaves were treated with a stain specific for pectin. This staining showed that there was an Experientia 42 (1986), Birkh//user Verlag, CH-4010 Basel/Switzerland especially high concentration of pectic substances in the phloem (intracellularly in companion cells and intercellularly between sieve tube elements). Greenbugs generally cause extensive damage to vascular tissues of susceptible varieties of their host plants H. Furthermore, greenbugs feed chiefly from the phloem of their host plants and possess salivary enzymes capable of depolymerizing a wide array of plant matrix polysaccharides (e.g. pectin, arabino-galactan, cellulose, etc.) 9. Hence, much of the hetero-oligosaccharides in greenbug honeydew are likely to be breakdown products of matrix polysaccharides in the phloem. It is possible, theretbre, that pectic fragments which escape being ingested by aphids are translocated elsewhere in the plant. Oligosaccharides produced from the depolymerization of plant cell walls have been found to elicit phytoalexin synthesis in a number of different plants ~2. More recently, oligouronides were shown to trigger synthesis of proteinase inhibitors ~3. Perhaps phloem translocation of specific hetero-oligosaccharides, produced by polysaccharase activity, is responsible for the variety of systemic responses commonly observed in plants infested by sap feeding insects TM or infected with bacteria and fungi ~s (e.g. premature senescence, gall formation, hypersensitivity, etc.). Summary. Two novel prenylated flavones, termed Cannflavin A and B, were isolated from the cannabinoid free ethanolic extract of Cannabis sativa L. Both compounds inhibited prostaglandin E2 production by human rheumatoid synovial cells in culture.