An organic electrolyte solution of 1.0 mol dm⁻³ LiCl/dimethyl sulfoxide (DMSO) was investigated for a fluorine-free battery with an electrode using 2,5-dimethoxy-1,4-benzoquinone (

) as the n-type active material and styrene butadiene rubber (SBR) as the binder. The electrodes showed the initial discharge capacities of 222 mAh g⁻¹ and 164 mAh g⁻¹ for the DMSO solution of the LiCl system and the LiPF₆ system, respectively. Moreover, they showed similar working voltages of 2.6–2.7 V, even though their plateau slopes had slight differences. In addition, the chemical bonding and crystallinity changes of were confirmed during discharge-charge, suggesting that it reacted electrochemically with Li⁺ in the LiCl/DMSO solution. The results of cycle properties suggested that a gradual decrease in the discharge capacities would result from denaturation and dissolution of during the redox process in the electrolyte solution.

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A spectrophotometric method for the determination of p-quinones was established with N,N-diethy-1,4-phenylenediamine. In the determination of 2,3-dimethoxy-5-methyl-1,4-benzoquinone (), Beer’s law was obeyed in a concentration range of 0.1∼1.5 μg/ml of . The apparent molar absorptivity was 1.1 × 10⁵ l mol^{− 1} cm^{− 1} at 552 nm. The relative standard deviation for six replicate determinations for 0.18 μg/ml was 0.48%.

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A new-type of oxidation–reduction condensation using alkyl diphenylphosphinites 1 and 2,6-di-tert-butyl-1,4-benzoquinone (DBBQ) proceeded smoothly under mild and neutral conditions by using nucleophiles such as nitrogen-, carbon- or sulfur-ones whose pK_a values were lower than 14. Various chiral molecules were successfully synthesized from chiral secondary or tertiary alkyl diphenylphosphinites in good to high yields with inversion of stereochemistry via S_N2 displacement. Effects of the substituents of 1,4-benzoquinones and the pK_a values of nucleophiles on these reactions have been investigated in detail.


(Contributed by Teruaki MUKAIYAMA, M.J.A.)

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Cytokinins are widely recognized as crucial phytohormones regulating plant growth and development by promoting cell division and differentiation. They are also known to be involved in inter-organism interactions, including the interaction between parasitic plants and host plants. Orobanchaceae parasitic plants form prehaustoria, primitive haustorial structures before host invasion, when in close proximity to the hosts. The induction of prehaustoria requires host-derived compounds, namely haustorium-inducing factors (HIFs), including quinones, phenolics and flavonoids, with structural similarity to lignin monomers. Notably, recent reports showed that cytokinins are capable to induce prehaustoria in the obligate parasitic plants in Orobanchaceae. Once prehaustoria invade into host roots, they become mature haustoria, which efficiently extract water and nutrients from the host. Cytokinins are also involved in this stage, as they are synthesized by parasitic plants and transported to host plants, causing hypertrophy and promoting efficient parasitism. In this review, we summarize the roles of cytokinins in the interaction between parasitic plants and host plants, with a specific focus on current understanding of prehaustorium induction, hypertrophy and germination of obligate parasites.

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Several parasitic plants in Orobanchaceae, such as Striga and Orobanche, cause devastating damage on agriculture worldwide. However, the molecular mechanisms of plant parasitism remain poorly understood. Orobanchaceae include species in a different range of parasitism, i.e. facultative and obligate parasites. Facultative parasites complete their life cycle without host plants, while obligate parasites are not able to survive without hosts in a natural condition. Although both parasites respond to quinone signals to develop infectious organs called haustoria, their shapes are distinct. Their responses to germination stimulants are also different. We are conducting genome and transcriptome analyses of an obligate parasite Striga asiatica and a facultative parasite Phtheirospermum japonicum to identify genes responsible for plant parasitism. A transformation protocol of P. japonicum was also established and used for functional characterization of parasitic plant genes.

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Striga spp. are noxious parasitic weeds that attack important crop species such as rice, maize and sorghum. Estimated yield losses can reach 1 billion US dollars annually. Striga belongs to the Orobanchaceae family, which contains approximately 90 genera of parasitic species. The degree of parasitism varied among species, from facultative parasites that can set seeds without host plants, to obligate holoparasites that cannot photosynthesize and thus completely depend on their hosts. The obligate parasites (e.g., Striga and Orobanche) germinate only when host plants are close by, via recognition of host-secreted strigolactones. The germinated parasitic plants develop an invasive haustorium on their roots. The haustoria penetrate host roots and establish vascular connections between hosts and parasites to absorb water and nutrients. Induction of haustorium is provoked by host-derived small compounds, named haustorium-inducing factors, including quinones and flavonoids. Diversity of germination stimulants and haustorium-inducing factors is likely to contribute to host recognition by parasitic plants. On the other hand, host plants respond to parasitic plants by activating plant immunity. This review focuses on the interaction between the parasites and their hosts.

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In this study, we sought to determine whether and how an α,β-unsaturated carbonyl, acrolein, can inhibit the growth of the cyanobacterium Synechocystis sp. PCC6803 (S. 6803). Treatment of S. 6803 with 200 µM acrolein for 3 d significantly and irreversibly inhibited its growth. To elucidate the inhibitory mechanism, we examined the effects of acrolein on photosynthesis. In contrast to dark conditions, the addition of acrolein to S. 6803 under conditions of illumination lowered the CO₂-dependent O₂ evolution rate (photosynthetic activity). Furthermore, treatment with acrolein lowered the activity reducing dimethyl benzoquinone in photosystem II (PSII). Acrolein also suppressed the reduction rate for the oxidized form of the reaction center chlorophyll of photosystem I (PSI), P700. These results indicate that acrolein inhibited PSII activity in thylakoid membranes. The addition of 200 µM acrolein to the illuminated S. 6803 cells gradually increased the steady-state level (Fs) of Chl fluorescence and decreased the quantum yield of PSII. These results suggested that acrolein damaged the acceptor side of PSII. On the other hand, acrolein did not inhibit respiration. From the above results, we gained insight into the metabolism of acrolein and its physiological effects in S. 6803.

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Effects of lipids and their related compounds on the chloroplast functions were investigated. Whole lipids, i.e. methyl linolenate, monogalactosyldiglyceride, and lecithin induced only a slight effect on the photochemical activities; electron transport, H⁺ uptake, and cyclic photophosphorylation. Lecithin alone stimulated significantly O₂ evolution. On the con-trary, the lipid-hydrolysis products, i.e. linolenic acid, monogalactosylmonoglyceride, and lysolecithin caused a strong inhibition of all the photoactivities tested. They showed two different modes of inhibition, which arise probably from a situation whether the lipids affect coupling factor or not besides the membrane part in thylakoid. Peroxidized methyl linolenate and α-tocopherol were also examined and the effect of lipid oxidation was discussed.

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  Barbatic acid, a lichen-derived depside, inhibited oxygen evolution in spinach thylakoid membranes. It also affected parameters of Chl fluorescence, (Fm′-F)/F and Fv/Fm. Using specific donors and acceptors of electrons, we found two sites of inhibition in the PS II complex. The primary site, which is responsible for the inhibition of oxygen evolution, is at the reducing side of Q_A, possibly at Q_B. The other site is at the oxidizing side of P680 but not in the oxygen evolving complex, suggesting Yz as the target. At both sites, irreversible binding of the depside to the targets seems to be responsible for the inhibitions. Among the 8 lichen acids compared, barbatic acid was the most potent inhibitor for both the reducing site and oxidizing site.

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In order to determine the allelopathic nature of lichen acids produced by lichen mycobionts, we compared lichen photobionts with other photosynthetic organisms in terms of inhibition of photosynthetic electron transport around photosystem II (PSII) by representative lichen acids. Whereas at the thylakoid level we found no clear difference in tolerance against lichen acids between lichen photobionts and other species, at the cellular level lichen photobionts showed strong tolerance as compared with other species. These findings suggest the presence of a lichen acid-specific exclusion or detoxification mechanism in lichen photobiont cells.

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Natural aurachin C is the most potent inhibitor of oxidation of ubiquinols by cytochromes bo and bd from Escherichia coli. To probe the structural properties of the substrate oxidation site in the ubiquinol oxidases, we synthesized a systematic set of aurachin C analogues (N-hydroxy-4-quinolone derivatives) and examined how their structure affects their activity towards cytochromes bo and bd, which are structurally unrelated. We found that the presence of the 3-methyl group of the 2-n-decyl and 2-n-undecyl derivatives increased the inhibitory potency towards both enzymes, probably due to a local steric congestion that allows favorable interaction of the alkyl tail with the enzyme. Increase in the chain length of the 3-alkyl tail of the 2-n-undecyl derivatives decreased the inhibitory potency only in cytochrome bo, indicating that the binding site for the alkyl tails of cytochrome bo is smaller than that of cytochrome bd. Based on these findings, we discuss the differences in the molecular mechanism of substrate oxidation by these two terminal ubiquinol oxidases.

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逆ミセルの媒質は巨視的には均一であるが、微視的には不均一であるため、特異な反応場は注目されている。今回はwater/AOT/heptane逆ミセルにおいて、光還元によりwater pool中に生成させたロイコメチレンブルーと2,6-ジブチルベンゾキノン(DBBQ)との間のヒドリド移動反応の速度をDBBQ大過剰の条件の下で分光学的に追跡した。二次速度定数k2(=kobs/[DBBQ]0)はwater poolの大きさW(=[water]/[AOT])が大きくなるにつれて増加する傾向が見られた。さらにAOT濃度効果などについても検討した。　

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根寄生植物は多くの穀物やマメ科作物を宿主とし, 世界各地で農業に甚大な被害をもたらしている. 根寄生植物種子は宿主植物の根から分泌される信号物質を感受してはじめて発芽する. これは宿主から独立しては生きられない根寄生植物が持つ巧妙な生存戦略と考えられている. 根寄生植物種子の発芽を刺激する物質について概説するとともに, 宿主認識における発芽刺激物質の重要性および発芽刺激物質を用いた根寄生植物の防除の可能性についてまとめた.

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