Ephemerality of a Spring Ephemeral Gagea lutea (L.) is Attributable to Shoot Senescence Induced by Free Linolenic Acid.

Spring ephemerals are a group of herbaceous plants that fulfill their life cycle on the floor of deciduous forests in temperate and boreal regions during a short period of time between snowmelt and closure of the tree canopy. Near the closure, these plants' shoots senesce rapidly and the plants disappear from the floor. Since the major role of the synchronous senescence is thought to be the recycling of nutrients from vegetative organs to seeds or storage organs, some endogenous compound that is capable of promoting senescence must be involved in the timely senescence. Strong senescence-promoting activity was found in extracts of shoots of a spring ephemeral, Gagea lutea (Liliaceae), and the activity in basal leaves reached a maximum just before the commencement of senescence. The active compound was identified as α-linolenic acid. The level, very low 1 week before flowering, increased rapidly with time and reached a maximum 1 week after flowering. Senescence was readily observed thereafter. The maximum amount of linolenic acid was >1 mmol kg FW-1 and could fully induce senescence of the leaves. The results suggest that the ephemerality of the plant or, in other words, short longevity of shoots, is brought about by the accumulation of linolenic acid. Programmed senescence, which can mitigate the cost of survival and reproduction, enables the plant to occupy a narrow niche on the forest floor.

Isolation and identification of an anti-bolting compound, hexadecatrienoic acid monoglyceride, responsible for inhibition of bolting and maintenance of the leaf rosette in radish plants.

Generally, the bolting (stem elongation from rosette plants) of winter annuals is believed to be induced by an increase in the levels of gibberellin that occurs after a certain period of chilling (vernalization), and a deficiency of gibberellin allows the plant to maintain a rosette style. Lack of direct evidence proving the above assumption in radish plants (Raphanus sativus L.) encouraged us to assume the presence of an anti-bolting compound actively maintaining the rosette habit through inhibition of bolting. Anti-bolting activity was detected in an extract of rosette shoots of radish plants by an assay using seedlings cultured in vitro. The causal compound that strongly inhibited bolting was isolated and identified as alpha-(7Z,10Z,13Z)-hexadecatrienoic acid monoglyceride (16:3 monoglyceride). This compound did not inhibit leaf production at the apical meristem, indicating that it merely inhibits growth at the internode. The compound disappeared completely after vernalization, and bolting occurred thereafter. The results suggest that the release from inhibition by 16:3 monoglyceride induces the initiation of bolting. The possible mechanism by which the compound exerts the activity is discussed.

Synthesis of a trigalacturonic acid analogue mimicking the expected transition state in the glycosidases.

A trigalacturonic acid analogue carrying a cyclohexene framework in place of the central pyranose ring was synthesized as a molecular probe for the mechanistic investigation of endo-polygalacturonase 1 (endo-PG 1). Preliminary enzymatic studies revealed that this analogue inhibited endo-PG 1 activity by about 30% at 0.3mM concentration.

Novel neofusapyrones isolated from Verticillium dahliae as potent antifungal substances.

Novel fusapyrone analogs, deoxyneofusapyrone and 7-desmethyldeoxyneofusapyrone were isolated from a pathogenic fungus, Verticillium dahliae, which causes Verticillium wilt disease in Helianthus annuus. Spectral analyses revealed that these are 2-pyrone type analogs of deoxyfusapyrone and its 7-desmethyl derivative, respectively. Biological assay disclosed that 10microg of deoxyneofusapyrone inhibited the growth of MRSA clinical isolate 87-7927.

Biosynthetic studies of spiroleptosphol.

Studies of the biosynthesis of spiroleptosphol (1) revealed that 1 comprised a heptaketide (C1, C5-C10, and C12-C18 moiety), two methyl carbons (C19 and C20) from methionine, and a C(3) unit (C3, C4, and C11 moiety) derived through the TCA cycle.

Isolation and absolute stereochemistry of optically active sydonic acid from Glonium sp. (Hysteriales, Ascomycota).

Optically active sydonic acid (1) was isolated for the first time from a culture broth of Glonium sp. The absolute stereochemistry was established to be (S) by comparing the circular dichroism (CD) spectrum with that of (+)-curcutetraol after conversion into (+)-sydonol (2).

Four analogues of spiroleptosphol isolated from Leptosphaeria doliolum.

Spiroleptosphol B (2), spiroleptosphol C (3), norleptosphol C (4) and hydroleptosphol (5) were isolated from ascomycete Leptosphaeria doliolum. Detailed (1)H and (13)C NMR spectral analyses revealed these were structural analogues of spiroleptosphol (1) which we have recently isolated from the same fungi. Spiroleptosphol B (2) carried an unprecedent 5,3-dioxatricyclo[4.4.0.1(1.4)]undecane framework in place of the spirobicyclo ring system of 1. Spiroleptosphol C (3) was a 17-(R)-hydroxy derivative of 1. Norleptosphol C (4) was deduced to be the monocyclic structure biosynthetically resulted by decarboxylation from 3. Although 5 gave broaden (1)H NMR spectrum, it was gradually transformed to 2 which suggested being a hydrolysate of 1.

Structure and biosynthesis of norneolambertellin produced by Lambertella sp. 1346.

Norneolambertellin (1) was isolated from a mycoparasite Lambertella sp. 1346. Combined analysis of the NMR spectra and chemical shift prediction based on molecular orbital calculation successfully revealed a novel pyrano[3,2-c]chromene-2,5-dione structure, which was further confirmed by X-ray crystallographic analysis. Isotopomer distribution analysis of the sample, prepared under labeling conditions, deduced its biosynthetic pathway.

Syntheses of lambertellols and their stable analogues; investigation of the real active species in the mycoparasitism by Lambertella species.

Lambertellols A (1) and B (2), isolated from mycoparasites Lambertella species, were synthesized. The synthesis features intramolecular aldol-type cyclizations of aldehydes 12 and 14 and site specific oxidations of 1-hydroxylambertellols as key steps. The synthesis also provided all diastereomers of 1-hydrolambertellols 17-19 and 25. Chiral resolution made the optically active forms available, which enabled the investigation of the real active species in the mycoparasitism by Lambertella species against Monilinia fructigena. These experiments suggested that lambertellin (3) is responsible for this phenomenon. Chemically labile 1 and 2 should be converted to 3 during the bioassay. The parasite may excrete 1 and 2 as readily diffusible forms, which are then transformed into 3 to inhibit the host M. fructigena. The parasite may have acquired this "drug delivery system" mechanism as an evolutionary enhancement.

Spiroleptosphol isolated from Leptosphaeria doliolum.

A novel gamma-methylidene-spirobutanolide spirolephtoshol (1) was isolated from ascomycetous fungus Leptosphaeria doliolum as a cytotoxic compound. The relative structure was established by the NMR analysis involving the NOE experiments. Absolute structure of the bicyclic moiety was determined by chemical derivation followed by the CD analysis. The relative and absolute stereochemistry of the side chain was established by comparison of the (1)H NMR spectra and the chiral GC chromatograms of the degradation product with the synthetic samples.

Stimulation of the biosynthesis of the antibiotics lambertellols by the mycoparasitic fungus Lambertella corni-maris under the acidic conditions produced by its host fungus in vitro.

The filamentous fungus, Lambertella corni-maris (L. corni-maris), a mycoparasite on Monilinia fructigena, produces the antibiotics, lambertellols A (1), B (2), and lambertellin (3), in a substantial amounts under acidic conditions, whereas these antibiotics were hardly detected when the fungus was cultured on a potato-sucrose (PS) medium without added acids. Our investigations also revealed that the host, M. fructigena, changed its surroundings into acidic conditions, suggesting that the acidic conditions acted as kairomones that stimulated the production of 1-3.

An antifungal compound involved in symbiotic germination of Cypripedium macranthos var. rebunense (Orchidaceae).

Germination of orchid seeds fully depends on a symbiotic association with soil-borne fungi, usually Rhizoctonia spp. In contrast to the peaceful symbiotic associations between many other terrestrial plants and mycorrhizal fungi, this association is a life-and-death struggle. The fungi always try to invade the cytoplasm of orchid cells to obtain nutritional compounds. On the other hand, the orchid cells restrict the growth of the infecting hyphae and obtain nutrition by digesting them. It is likely that antifungal compounds are involved in the restriction of fungal growth. Two antifungal compounds, lusianthrin and chrysin, were isolated from the seedlings of Cypripedium macranthos var. rebunense that had developed shoots. The former had a slightly stronger antifungal activity than the latter, and the antifungal spectra of these compounds were relatively specific to the nonpathogenic Rhizoctonia spp. The level of lusianthrin, which was very low in aseptic protocorm-like bodies, dramatically increased following infection with the symbiotic fungus. In contrast, chrysin was not detected in infected protocorm-like bodies. These results suggest that orchid plants equip multiple antifungal compounds and use them at specific developmental stages; lusianthrin maintains the perilous symbiotic association for germination and chrysin helps to protect adult plants.