Biomedical subjects
Publications and source records attributed to Kohki Akiyama.
10-Phenyl-[11]-cytochalasans (4-6), together with three known derivatives (1-3), were isolated from the MeOH extract of the Indonesian mushroom Microporellus subsessilis by a bioassay-guided fractionation. The compounds 6 and 1-3 induced immotility in Artemia salina.
AIMS: Arbuscular mycorrhizae are formed between >80 % of land plants and arbuscular mycorrhizal (AM) fungi. This Botanical Briefing highlights the chemical identification of strigolactones as a host-recognition signal for AM fungi, and their role in the establishment of arbuscular mycorrhizae as well as in the seed germination of parasitic weeds. SCOPE: Hyphal branching has long been described as the first morphological event in host recognition by AM fungi during the pre-infection stages. Host roots release signalling molecules called 'branching factors' that induce extensive hyphal branching in AM fungi. Strigolactones exuded from host roots have recently been identified as an inducer of hyphal branching in AM fungi. Strigolactones are a group of sesquiterpenes, previously isolated as seed germination stimulants for the parasitic weeds Striga and Orobanche. Parasitic weeds might find their potential hosts by detecting strigolactones, which are released from plant roots upon phosphate deficiency in communication with AM fungi. In addition to acting as a signalling molecule, strigolactones might stimulate the production of fungal symbiotic signals called 'Myc factors' in AM fungi. CONCLUSIONS: Isolation and identification of plant symbiotic signals open up new ways for studying the molecular basis of plant-AM-fungus interactions. This discovery provides a clear answer to a long-standing question in parasitic plant biology: what is the natural role for germination stimulants? It could also provide a new strategy for the management and control of beneficial fungal symbionts and of devastating parasitic weeds in agriculture and natural ecosystems.
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Arbuscular mycorrhizal (AM) fungi form mutualistic, symbiotic associations with the roots of more than 80% of land plants. The fungi are incapable of completing their life cycle in the absence of a host root. Their spores can germinate and grow in the absence of a host, but their hyphal growth is very limited. Little is known about the molecular mechanisms that govern signalling and recognition between AM fungi and their host plants. In one of the first stages of host recognition, the hyphae of AM fungi show extensive branching in the vicinity of host roots before formation of the appressorium, the structure used to penetrate the plant root. Host roots are known to release signalling molecules that trigger hyphal branching, but these branching factors have not been isolated. Here we have isolated a branching factor from the root exudates of Lotus japonicus and used spectroscopic analysis and chemical synthesis to identify it as a strigolactone, 5-deoxy-strigol. Strigolactones are a group of sesquiterpene lactones, previously isolated as seed-germination stimulants for the parasitic weeds Striga and Orobanche. The natural strigolactones 5-deoxy-strigol, sorgolactone and strigol, and a synthetic analogue, GR24, induced extensive hyphal branching in germinating spores of the AM fungus Gigaspora margarita at very low concentrations.
In a screening study on immunomodulatory fungal constituents, eleven new 2-pyrones tentatively named TT-1 (1), and TT-2-11 (2-11) have been isolated from a Fungi Imperfecti, Trichurus terrophilus, and designated rasfonin (1), and trichurusin B-K (2-11), respectively. Compounds 1-4 exhibited considerably high immunosuppressive activities, and compounds 8-11 have shown moderate ones. The structure-activity relationships of these constituents have also been discussed.
Rice (Oryza sativa var. Nipponbare) was transformed with an artificial avidin gene. The features of this construct are as follows: (1) a signal peptide sequence derived from barley alpha amylase was added at the N-terminal region, (2) codon usage of the gene was optimized for rice, and (3) the gene was driven by rice glutelin GluB-1, an endosperm-specific promoter. Avidin was produced in the grain of the transgenic rice but not in the leaves. The concentration of avidin in the kernels was about 1,800 ppm. All larvae of the confused flour beetle (Tribolium confusum) and Angoumois grain moth (Sitotroga cerealella) died when fed transgenic avidin rice powder or kernels, respectively, whereas most of the test insects developed into adults when they were fed a nontransgenic rice control diet. Avidin extracted from the transgenic rice kernel lost most biotin-binding activity after 5 min heating at 95 degrees C.
The ethyl acetate extract of the whole aerial parts of Varthemia iphionoides (Compositae) showed a pronounced antibacterial activity. The bioassay-guided fractionation of the ethyl acetate extract and further purification of the most antibacterially active fraction led to the isolation and identification of an antibacterial sesquiterpene, selina-4,11(13)-dien-3-on-12-oic acid. This compound exhibited potent antimicrobial activity against six bacterial species (Staphylococcus aureus, Bacillus subtilis, Micrococcus luteus, Escherichia coli, Bacillus cereus and Salmonella enteritides). The minimum inhibitory concentrations (MICs) of this compound which was determined by the agar dilution method ranged between 250 and 500 microg/ml.
Three new communesin congeners, communesins C, D, and E, together with two known communesins A and B were isolated from okara that had been fermented with Penicillium expansum Link MK-57. All these communesins showed the insecticidal activity against the silkworms.
Three new dimeric naphthopyrones, asperpyrones A (1), B (2), and C (3), together with two known compounds, fonsecinone A (4) and aurasperone A (5), have been isolated from okara that was fermented with Aspergillus niger JV-33-48. Compounds 1, 4, and 5 showed inhibitory activity on Taq DNA polymerase.
Melon (Cucumis melo) roots were inoculated with or without the arbuscular mycorrhizal (AM) fungus Glomus caledonium under low phosphate conditions. High-performance liquid chromatography analysis of the secondary metabolites in butanol extracts from roots revealed that the level of one compound in noninoculated roots showed a significant increase from 30 days postinoculation. No accumulation was observed in mycorrhizal roots and high-phosphate-supplemented roots, indicating that the accumulation of the compound was caused by a phosphate deficiency. The compound was isolated by column chromatography and identified by spectroscopic methods to be a C-glycosylflavone, isovitexin 2''-O-beta-glucoside. The effect of the compound on mycorrhizal colonization in melon roots was examined under low (0.05 mM) and high (2 mM) phosphate conditions. The degree of mycorrhizal colonization in control roots grown under high phosphate conditions (8.8%) was much lower than when grown under low phosphate conditions (22%). The treatment of roots with the compound at concentrations of 20 and 50 microM increased root colonization under both low and high phosphate conditions. In particular, the degrees of mycorrhizal colonization in treated roots grown under high phosphate conditions (25 and 22% at 20 and 50 microM, respectively) were comparable to that in untreated control roots grown under low phosphate conditions (22%). These findings suggest that the phosphate deficiency-induced C-glycosylflavonoid is involved in the regulation of AM fungal colonization in melon roots.
New convulsive compounds, brasiliamides A (1) and B (2), were isolated by activity-guided fractionation from okara fermented with a soil isolate of Penicillium brasilianum Batista JV-379. Their structures were elucidated on the basis of spectral and chemical evidence and by X-ray crystallography of the hydrogenated product of 2. In the 1H- and 13C-NMR spectra of 2, the signals were complicated, all being doubled or broadened in several deuterated solvents at room temperature. The conformational change of 2 was clarified as the rotational isomerization of amide bonds in solution by NMR measurements at various temperatures. Four rotamers of 2 at two amide bonds were presented at -60 degrees C in CDCl3, whereas only two isomers were apparent at room temperature, owing to rapid rotation of one of the amide bonds. Brasiliamides A and B respectively showed convulsive activity against silkworms with ED50 values of 300 and 50 microg/g of diet.
Cucumber (Cucumis sativus L.) roots were analyzed by HPLC and TLC for their levels of secondary metabolites upon inoculation with the arbuscular mycorrhizal fungus, Glomus caledonium. Three compounds in EtOAc extracts from the mycorrhizal roots showed significant increases six weeks after inoculation. These compounds were isolated by column chromatography and determined to be two novel triterpenes, 2beta-hydroxybryonolic acid (2beta,3beta-dihydroxy-D:C-friedoolean-8-en-29-oic acid) and 3beta-bryoferulic acid [3beta-O-trans-ferulyl-D:C-friedooleana-7,9(11)-diene-29-oic acid], and the known triterpene, bryonolic acid, by spectroscopic methods. Time-course experiments showed that the levels of the three terpenoids in cucumber roots were significantly increased by the application of a 53-microm sieving from a soil inoculum of the arbuscular mycorrhizal fungus containing soil microbes but no mycorrhizal fungi, and that mycorrhizal colonization further promoted the terpenoid accumulation. Inoculation with Glomus mosseae also enhanced the accumulation of the triterpenes, whereas no accumulation was observed by inoculating with the fungal pathogen, Fusarium oxysporum f. sp. cucumerinum. 2Beta-hydroxybryonolic acid was also isolated from the roots of melon and watermelon.