Satoshi Tahara

Suppression of Damping-Off Disease in Host Plants by the Rhizoplane Bacterium Lysobacter sp. Strain SB-K88 Is Linked to Plant Colonization and Antibiosis against Soilborne Peronosporomycetes

ABSTRACT We previously demonstrated that xanthobaccin A from the rhizoplane bacterium Lysobacter sp. strain SB-K88 suppresses damping-off disease caused by Pythium sp. in sugar beet. In this study we focused on modes of Lysobacter sp. strain SB-K88 root colonization and antibiosis of the bacterium against Aphanomyces cochlioides, a pathogen of damping-off disease. Scanning electron microscopic analysis of 2-week-old sugar beet seedlings from seeds previously inoculated with SB-K88 revealed dense colonization on the root surfaces and a characteristic perpendicular pattern of Lysobacter colonization possibly generated via development of polar, brush-like fimbriae. In colonized regions a semitransparent film apparently enveloping the root and microcolonies were observed on the root surface. This Lysobacter strain also efficiently colonized the roots of several plants, including spinach, tomato, Arabidopsis thaliana, and Amaranthus gangeticus. Plants grown from both sugar beet and spinach seeds that were previously treated with Lysobacter sp. strain SB-K88 displayed significant resistance to the damping-off disease triggered by A. cochlioides. Interestingly, zoospores of A. cochlioides became immotile within 1 min after exposure to a SB-K88 cell suspension, a cell-free supernatant of SB-K88, or pure xanthobaccin A (MIC, 0.01 μg/ml). In all cases, lysis followed within 30 min in the presence of the inhibiting factor(s). Our data indicate that Lysobacter sp. strain SB-K88 has a direct inhibitory effect on A. cochlioides, suppressing damping-off disease. Furthermore, this inhibitory effect of Lysobacter sp. strain SB-K88 is likely due to a combination of antibiosis and characteristic biofilm formation at the rhizoplane of the host plant.

Fungitoxic dihydrofuranoisoflavones and related compounds in white lupin, Lupinus albus☆

Abstract Chromatographic investigation of a methanolic extract of white lupin roots has revealed the presence of six new dihydrofuranoisoflavones (lupinisoflavones A-F). Three monoprenylated (3,3-dimethylallyl-substituted) isoflavones (wighteone, luteone and licoisoflavone A), two diprenylated isoflavones [6,3′-di(3,3-dimethylallyl)genistein (lupalbigenin) and 6,3′-di(3,3-dimethylallyl)-2′-hydroxygenistein (2′-hydroxylupalbigenin)] and two pyranoisoflavones (parvisoflavone B and licoisoflavone B) have also been isolated from the same source. In addition to genistein, leaf extracts of L. italbus contain 3′-O-methylorobol which is presumed to be the precursor of lupisoflavone [5,7,4′-trihydroxy-3′-methoxy-6-(3,3-dimethylallyl)isoflavone]. Probable biogenetic relationships between the prenylated, and dihydrofurano-and pyrano-substituted isoflavones in roots and leaves of L. albus are briefly discussed.

Saponins from the roots of Panax notoginseng

Abstract The glycosidic fraction from the dried roots of Panax notoginseng (Burk.) F.H.Chen exhibited an inhibitory effect on zoospore motility of Aphanomyces cochlioides . Further study on this fraction afforded fourteen dammarane-type saponins. Their structures were determined on the basis of spectroscopic and chemical methods. Eleven were known compounds, and the three new ones were 3- O -[β- d -glucopyranosyl (1→6)-β- d -glucopyranosyl]-20- O -β- d -glucopyranosyl 3β, 12β, 20 ( S )-trihydroxydammar-24-ene, 3- O -β- d -glucopyranosyl 20- O -[α- l -arabinopyranosyl (1→2)-β- d -glucopyranosyl] 3β, 12β, 20 ( S )-trihydroxydammar-24-ene and 6- O -β- d -glucopyranosyl 20- O -β- d -glucopyranosyl 3β, 6α, 12β, 20 ( S ), 25-pentahydroxydammar-23-ene, respectively. Each saponin displayed good inhibitory effects on zoospore motility.

A Journey of Twenty-Five Years through the Ecological Biochemistry of Flavonoids

The ecological biochemistry of flavonoids, in which I have been engaged for 25 years, is summarized in this review article. The review covers (1) a survey of rare bio-active flavonoids in higher plants; (2) the fungal metabolism of prenylated flavonoids; (3) flavonoids antidoting against benzimidazole fungicides; (4) dihydroflavonol ampelopsin in Salix sachalinensis as a feeding stimulant towards willow beetles; and (5) flavones as signaling substances in the life-cycle development of the phytopathogenic Peronosporomycete Aphanomyces cochlioides, a cause of spinach root rot and sugar beet damping-off diseases. Finally recent trends in the ecological biochemistry of flavonoids are briefly described.

Isoflavonoids produced by Iris pseudacorus leaves treated with cupric chloride

Abstract Iris pseudacorus leaves treated with cupric chloride produced fungitoxic stress metabolites. They were found to be 10 isoflavones [5,2′-dihydroxy-6,7-dimethoxyisoflavone (irilin A), 5,7,2′-trihydroxy-6-methoxyisoflavone (irilin B), 5,7,2′-trihydroxyisoflavone (irilin C), iristectorigenins A and B, tectorigenin, 3′- O -methylorobol, pratensein, biochanin A and genistein] and six coumaronochromones [5,7-dihydroxy-6-methoxycoumaronochromone, 5,7-dihydroxycoumaronochromone, 5,7,3′-trihydroxycoumaronochromone, 5,7,4′-trihydroxy-6-methoxycoumaronochromone (ayamenins A–D, respectively), 5,7,3′-trihydroxy-6-methoxycoumaronochromone and lupinalbin A]. Irilins A–C and ayamenins A–D are new compounds. This is the first report on stress metabolites from the Iridaceae.

Shizukaol A, A sesquiterpene dimer from Chloranthus japonicus

Abstract A novel dimeric sesquiterpene consisted of two lindenane (modified eudesmane) units was isolated from roots of Chloranthus japonicus . The structure was elucidated by 1D and 2D NMR analyses and by chemical methods.

Biochemical characterization of rice trehalose-6-phosphate phosphatases supports distinctive functions of these plant enzymes.

Substantial levels of trehalose accumulate in bacteria, fungi, and invertebrates, where it serves as a storage carbohydrate or as a protectant against environmental stresses. In higher plants, trehalose is detected at fairly low levels; therefore, a regulatory or signaling function has been proposed for this molecule. In many organisms, trehalose‐6‐phosphate phosphatase is the enzyme governing the final step of trehalose biosynthesis. Here we report that OsTPP1 and OsTPP2 are the two major trehalose‐6‐phosphate phosphatase genes expressed in vegetative tissues of rice. Similar to results obtained from our previous OsTPP1 study, complementation analysis of a yeast trehalose‐6‐phosphate phosphatase mutant and activity measurement of the recombinant protein demonstrated that OsTPP2 encodes a functional trehalose‐6‐phosphate phosphatase enzyme. OsTPP2 expression is transiently induced in response to chilling and other abiotic stresses. Enzymatic characterization of recombinant OsTPP1 and OsTPP2 revealed stringent substrate specificity for trehalose 6‐phosphate and about 10 times lower Km values for trehalose 6‐phosphate as compared with trehalose‐6‐phosphate phosphatase enzymes from microorganisms. OsTPP1 and OsTPP2 also clearly contrasted with microbial enzymes, in that they are generally unstable, almost completely losing activity when subjected to heat treatment at 50 °C for 4 min. These characteristics of rice trehalose‐6‐phosphate phosphatase enzymes are consistent with very low cellular substrate concentration and tightly regulated gene expression. These data also support a plant‐specific function of trehalose biosynthesis in response to environmental stresses.

Antifungal stress compounds from Veratrum grandiflorum leaves treated with cupric chloride

Abstract Two antifungal stilbenoids and their glucosides were isolated from the leaves of Veratrum grandiflorum treated with cupric chloride. They were identified as resveratrol, oxyresveratrol, resveratrol-3- O -glucoside (piceid) and oxyresveratrol-3- O -glucoside. The last compound was isolated for the first time from a natural source. In addition three glucosides of flavonoid (apigenin-7- O -glucoside, luteolin-7- O -glucoside, chrysoeriol-7- O -glucoside) were also found in the leaves.

Chemotaxis of fungal zoospores, with special reference to Aphanomyces cochlioides

Zoospores of phytopathogenic fungi accumulate at the potential infection sites of host roots by chemotaxis. The aggregated spores then adhere, encyst, germinate, and finally penetrate into the root tissues to initiate infection. Some of the host-specific attractants have already been identified. The host-specific attractants also induce cell differentiation of certain zoospores under laboratory conditions. This indicates that a signal released from the roots of the host plant guides the pest propagules for orientation and prepares them for establishing a host-pathogen relationship by necessary physiological changes. Some non-host plant secondary metabolites were found to markedly regulate behavior and viability of zoospores, suggesting that non-host compounds may also play a role in protecting the non-host plants from the attack of zoosporic fungi. We hypothesized that zoospores perceive the host signal(s) by specific G-protein-coupled receptors and translate it into responses by way of the phosphoinositide-Ca2+ signaling cascade. The details of the signal transduction mechanism in fungal zoospores are yet to be discovered. In this report, we review the signaling and communications between phytopathogenic fungal zoospores and host and non-host plants with special reference to Aphanomyces cochlioides.

Highly oxidized cuparene-type sesquiterpenes from a mycelial culture of Flammulina velutipes.

Cuparene-type sesquiterpenes were isolated from a culture broth of Flammulina velutipes (Curt.:Fr.) Sing. Using spectroscopic methods (HR-MS, 1H and 13C NMR, and 2D NMR, spectroscopy), their structures were determined to be 2,3,4,5-tetrahydro-2,7-dihydroxy-5,8,10,10-tetramethyl-2,5-methano-1- benzoxepin and 5-methyl-2-(3-oxo-1,2,2-trimethylcyclopentyl)benzoquinone. Both showed antimicrobial activity against Cladosporium herharum and Bacillus subtilis.