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941.
Kaempferol and quercetin 3-O-glucosides and 3-O-rhamnoglucosides are common to both Loxsoma cunninghamii and Loxsomopsis costaricensis, but in the former the new flavonoid glycosides, kaempferol and quercetin 3-O-glucoside-7-O-arabinoside have also been identified. The data are consistent with the proposed taxonomic relationship between these geographically isolated genera. Comparative flavonoid chemistry indicates that the Loxsomaceae may be a primitive family, not closely related to the Hymenophyllaceae or the Cyatheaceae. 相似文献
942.
Two isorhamnetin glycosides and two sulphated derivatives are reported for the first time in the genus Senecio. 相似文献
943.
Diomi Mamma Dimitris G. Hatzinikolaou Paul Christakopoulos 《Journal of Molecular Catalysis .B, Enzymatic》2004,27(4-6):183-190
In the presence of rutin as sole carbon source, Penicillium decumbens produces two intracellular β-glucosidases named GI and GII, with molecular masses of 56,000 and 460,000 Da, respectively. The two proteins have been purified to homogeneity. GI and GII composed of two and four equal sub-units, respectively and displayed optimal activity at pH 7.0 and temperature 65–75 °C. Both β-glucosidases were competitively inhibited by glucose and glucono-δ-lactone. GI and GII exhibited broad substrate specificity, since they hydrolyzed a range of (1,3)-, (1,4)- and (1,6)-β-glucosides as well as aryl β-glucosides. Determination of kcat/Km revealed that GII hydrolyzed 3–8 times more efficiently the above-mentioned substrates. The ability of GI and GII to deglycosylate various flavonoid glycosides was also investigated. Both enzymes were active against flavonoids glycosylated at the 7 position but GII hydrolyzed them 5 times more efficiently than GI. Of the flavanols tested, both enzymes were incapable of hydrolyzing quercetrin and kaempferol-3-glucoside. The main difference between GI and GII as far as the hydrolysis of flavanols is concerned, was the ability of GII to hydrolyze the quercetin-3-glucoside. 相似文献
944.
The cardenolides of the aerial parts of Asclepias linaria were isolated and identified as the known calactin, calotoxin, proceroside, gomphoside, desglucouzarin and the new cardenolide 6′-β-coumaroyl desglucouzarin. 相似文献
945.
Abstract. 1. Female monarchs were observed in the field ovipositing on a native North American milkweek host, Asclepias humistrata L. As in a comparable Australian study on an introduced novel host ( Asclepias fruticosa L.) we found post-alighting rejection of plants with low and high cardiac glycoside concentration (CG).
2. Most oviposition took place on plants with CG in the range 200–500 μg/0.1 g dry weight. Thin-layer chromatography showed no obvious qualitative difference in cardenolide types between accepted and rejected plants, excepting an indication that rejected plants may have a higher level of more polar cardenolides.
3. In a controlled laboratory experiment comparing oviposition on a low ( A.incarnata L.) vs high ( A.curassavica L.) CG host plant species we found no relationship between CG and oviposition on the low CG species, but a negative relationship in the high CG species. This corroborates our findings on oviposition on single host species in the field.
4. We also record the first indication of a physiological cost of monarch larvae feeding on plants high in CG. There was a significant negative relationship between survival of first instar larvae and CG levels in plants. This study opens the way for further work on the association of monarch butterflies and their toxic milkweed hosts. 相似文献
2. Most oviposition took place on plants with CG in the range 200–500 μg/0.1 g dry weight. Thin-layer chromatography showed no obvious qualitative difference in cardenolide types between accepted and rejected plants, excepting an indication that rejected plants may have a higher level of more polar cardenolides.
3. In a controlled laboratory experiment comparing oviposition on a low ( A.incarnata L.) vs high ( A.curassavica L.) CG host plant species we found no relationship between CG and oviposition on the low CG species, but a negative relationship in the high CG species. This corroborates our findings on oviposition on single host species in the field.
4. We also record the first indication of a physiological cost of monarch larvae feeding on plants high in CG. There was a significant negative relationship between survival of first instar larvae and CG levels in plants. This study opens the way for further work on the association of monarch butterflies and their toxic milkweed hosts. 相似文献