The oligosaccharide elicitor from the mycelial wall of an endophytic Colletotrichum sp. B501 promoted the production of artemisinin in Artemisia annua L. hairy root culture. When hairy roots of 22-day-old cultures (later growth phase) were exposed to the elicitor (20 mg/L) for 4 d, the maximum content of artemisinin reached 1.15 mg/g, a 64.29% increment over the control. The electron X-ray microanalysis disclosed the rapid accumulation of Ca 2+ in the elicited cortical cells of hairy root. The electronic microscope observation revealed the high electron density area in vacuole of elicited cells. During the first day of elicitation the peroxidase activity of hairy roots was improved sharply. Some cellular morphological changes including cell shrinkage, condensation of cytoplasm and nuclear fragmentation, coincident with the appearance of DNA ladders, were observed after the third day of elicitation. It was suggested that the oligosaccharide elicitor triggered the programmed cell death, which may provide the substance or chemical signal for artemisinin biosynthesis.
In addition to six known flavonoids quercitrin, hyperoside, avicularin, rutin, quercetin and kaemferol, a new flavonol glycoside named 6″_O_acetyl quercetin 3_O_β_ D _alloside (1) was isolated from the aerial parts of Hypericum perforatum L. The structures were determined on the basis of spectroscopic methods (UV, IR, FAB_MS, 1H_NMR and 13 C NMR). Antifungal assay of all compounds showed that metabolite 1, quercitrin and quercetin were inhibitory to the growth of phytopathogenic fungus Helminthosporium sativum Pamel King et Bakke with minimum inhibitory concentrations (MICs) of 25, 50 and 50 μg/mL, respectively. Moreover, glycoside 1 and quercitrin were also shown to be able to inhibit the growth of Fusarium graminearum Schw. with MIC of 100 μg/mL. The MICs of ketoconazole used as control against the test fungi were 0.5 μg/mL in our assay.
