Tamio Ueno

The production of phytoalexins by oat in response to crown rust, Puccinia coronata f. sp. avenae

The antifungal compounds accumulated only in the incompatible host-parasite combinations; the time of rapid accumulation coincided with the time of the retardation of the growth of infection hyphae. Three major compounds were isolated. They are highly hydrophilic nitrogen-containing phenolics. Their antifungal activities against Puccinia coronata avenae and P. graminis tritici were demonstrated. They were regarded as phytoalexins and given the trivial names avenalumins I, II, and III. Avenalumins are the first nitrogen-containing phytoalexins found in plants and they are the first chemically-identified ones found in cereal plants in response to rust fungi.

Inhibition of [3H]ponasterone A binding by ecdysone agonists in the intact Sf-9 cell line.

Ecdysone agonists, including dibenzoylhydrazines, significantly inhibited the binding of [(3)H]ponasterone A ([(3)H]PoA) in intact Sf-9 cells (Spodoptera frugiperda). The amount of [(3)H]PoA binding varied in a concentration-dependent manner. According to the IC(50), concentration at which there is 50% inhibition, the order of potency of typical ecdysone agonists is tebufenozide (RH-5992) > methoxyfenozide (RH-2485) > PoA > 20-hydroxyecdysone > cyasterone > RH-5849, makisterone A > or = inokosterone > ecdysone. The ranking is consistent with that obtained from a cultured integument system of the rice stem borer Chilo suppressalis except for methoxyfenozide. Other compounds whose modes of action are different from that of ecdysteroids, for example respiration inhibitors, plant steroid hormones, and chitin synthesis inhibitors, did not inhibit the binding of [(3)H]PoA significantly. The mammalian hormones estradiol and diethylstilbestrol, and a secondary bile acid, lithocholic acid, significantly inhibited the binding of [(3)H]PoA at 25 microM. However, their binding activity in terms of pIC(50) was either very low or not evaluated.

Prediction of the binding mode of imidacloprid and related compounds to house-fly head acetylcholine receptors using three-dimensional QSAR analysis

The binding activity of imidacloprid and related compounds to nico- tinic acetylcholine receptors (nAChR) of house Nies was measured by use of radioactive a-bungarotoxin as a ligand. Variations in the activity were examined three-dimensionally using comparative molecular -eld analysis (CoMFA). The CoMFA results suggest that one conformer among the four stable ones is active and provide support for one of the proposed binding models for this class of compound, in which the nitrogen atom of the pyridine ring and the nitrogen atom at the 1-position of the imidazolidine ring interact with the hydrogen- donating and electron-rich sites of nAChR, respectively. The CoMFA -eld map showed that the nitroimino moiety and a portion of the imidazolidine ring were mainly surrounded by a sterically and electrostatically sensitive region of nAChR. 1998 Society of Chemical Industry ( Pestic. Sci., 54, 134E144 (1998)

Inhibition of [3H]ponasterone A binding by ecdysone agonists in the intact Kc cell line

Inhibition of the binding of [3H]ponasterone A ([3H]PoA) by ecdysone agonists including diacylhydrazines such as RH-5849, tebufenozide (RH-5992) and methoxyfenozide (RH-2485) was examined in intact Drosophila Kc cells. The reciprocal logarithm of the concentration at which there is 50% inhibition of [3H]PoA binding, pIC(50) (M), was determined as the binding activity for all compounds from each concentration-response curve. The order of the activity was PoA>20-hydroxyecdysone>cyasterone>inokosterone>or=makisterone A>methoxyfenozide>or=tebufenozide>ecdysone>RH-5849. The ranking of steroidal ecdysone analogs is consistent with that obtained against Spodoptera Sf-9 cells. Furthermore, in terms of pIC(50), all binding activity for ecdysone analogs, except ecdysone, estimated in the Kc cell line system was significantly higher than that for the Sf-9 cell line system. However, the activity of ecdysone was comparable between Kc and Sf-9 cells. The activity of diacylhydrazine analogs against Kc cells was significantly low compared with that against Sf-9 cells. The potency of methoxyfenozide was 1/200 that of PoA, which showed the highest activity in the Kc cell line system among all compounds tested. The activity of tebufenozide analogs having an n-pentyl or n-hexyl group instead of a 4-ethylphenyl group was similar to that of RH-5849.

Induction of hydroxyanthranilate hydroxycinnamoyl transferase activity by oligo-N-acetylchitooligosaccharides in oats

Abstract An assay method for hydroxycinnamoyl-CoA: hydroxyanthranilate N -hydroxycinnamoyl transferase (HHT) in oat leaves ( Avena sativa L.), which is thought to be one of the key enzymes for the biosynthesis of avenanthramides, phytoalexins in this plant, was established. HHT activitiy was induced by treating the leaves with oligo- N -acetylchitooligosaccharides. Among the chitooligosaccharides tested, penta- N -acetylchitopentaose ((GlcNAC) 5 ) was the most effective in inducing activity. The induction by (GlcNAc) 5 was dose-dependent, in which case HHT activity was initially detected after 6 hr and reached a maximum by 12 hr. All of the putative precursors of avenanthramides acted as substrates for HHT, with 5-hydroxyanthranilic acid and feruloyl-CoA being the best substrates for the anthranilic moiety and the cinnamoyl moiety of avenanthramides, respectively.

Quantitative structure-activity studies of insect growth regulators, XVI: substituent effects of dibenzoylhydrazines on the insecticidal activity to Colorado potato beetle Leptinotarsa decemlineata

Insecticidal activity against the Colorado potato beetle, Leptinotarsa decemlineata, was measured for a series of substituted N-tert-butyl-dibenzoylhydrazines, in which one of the benzoyl moieties closer to the tert-butyl group was fixed as being 2-chloro-substitued and the other variously substituted singly or doubly. The effects of substituents on the activity were quantitatively analysed using the classical quantitative structure–activity relationship (QSAR) procedure. The activity against the Colorado potato beetle increases with the molecular hydrophobicity. In addition, various types of steric effect are at work, depending upon the positions. Hydrogen-bonding acceptor substituents at the para position enhance the activity. There seem to be threshold (or optimum) values, albeit position-dependent, in the molecular hydrophobicity, above which the activity starts to decrease. This biphasic contribution of the molecular hydrophobicity to activity against coleopterous larvae is the most conspicuous difference in substituent effects from those found for similar compounds against lepidopterous pest insects, and may be the basis of the variations in the activity spectrum for certain compounds in this series. The introduction of bulkier substituents into the meta- and para-positions of the benzene ring, apart from the tert-butyl group, is unfavorable to activity. LD50 values against Colorado potato beetle larvae of methoxyfenozide (RH-2485) and tebufenozide (RH-5992) were in the order of 10−7 mol per insect, whereas those of RH-5849, and halofenozide (RH-0345) were very low, 10−9–10−10 mol per insect being selective to the coleopterous larvae. © 1999 Society of Chemical Industry

Involvement of Ca2+ ion in phytoalexin induction in oats

Abstract The involvement of cytosolic Ca2+ in the signal transduction mechanism of phytoalexin induction was examined in oats. The treatment with a calcium ionophore, A23187, strongly induced the accumulation of avenanthramide A, a major phytoalexin in oats, in a dose-dependent manner. The induction of avenanthramide A by A23187 was suppressed by Mn2+ and EGTA, suggesting that the elevation of cytosolic Ca2+ by the ionophore caused phytoalexin production. The effects of various inhibitors of Ca2+-dependent processes on the elicitor activity of penta-N-acetylchitopentaose ((GlcNAc)5) were also examined. Treatment of oat leaf segments with three calcium channel blockers, LaCl3, verapamil and nifedipine inhibited the phytoalexin induction by (GlcNAc)5 at sub-millimolar levels. TMB-8 and ruthenium red, inhibitors of intracellular calcium movement, also abolished the phytoalexin induction. These findings indicate that Ca2+ is involved in the induction of the plant responses by elicitors.

Structure elucidation of AK-toxins, host-specific phytotoxic metabolites produced by alternaria kikuchiana tanaka

Abstract The structures of two host-specific phytotoxic metabolites, AK-toxin I and II, isolated from culture broth of Alternaria kikuchiana Tanaka (the fungus causing black spot disease of Japanese pear) were determined to be the ester consisting of N-acetyl-β-methyl-phenylalanine and 9,10-epoxy-8-hydroxy-9-methyl-2E, 4Z, 6E-decatrienoic acid ( 1 ) and its β-demethyl derivative ( 2 ).

Three-dimensional quantitative structure: activity relationship analysis of acyclic and cyclic chloronicotinyl insecticides

The binding activity of chloronicotinyl insecticides, including acetamiprid, nitenpyram and related compounds, to the nicotinic acetylcholine receptors (nAChR) of houseflies was measured. These compounds were defined as ‘acyclic’ compounds. Variations in the binding activity were analysed using comparative molecular field analysis (CoMFA) which is a technique for the analysis of three-dimensional quantitative structure–activity relationships. The CoMFA results showed that steric interactions were more significant for the acyclic compounds than for imidacloprid and its derivatives (cyclic compounds). It was also shown that the acyclic compounds could bind to housefly-nAChR in a similar manner to the cyclic compounds, and that the electrostatic natures of the acyclic amino- and cyclic imdazolidine-moieties affected their binding activity. © 2000 Society of Chemical Industry

Isolation and structure elucidation of genuine oat phytoalexin, avenalumin I

Abstract The major phytoalexin from oat leaves has been identified as 2-[2-(4-hydroxyphenyDethenyl] -6-hydroxy-4H-3,1-benzoxazin-4-one ( A ).