Katsuichiro Kobayashi

Accumulation of some nitrogen compounds in response to salt stress and their relationships with salt tolerance in rice (Oryza sativa L.) seedlings

The salt-induced accumulation of some nitrogen compounds (free amino acids, ammonium and urea) in shoots of eight rice cultivars differing in salt tolerance was investigated. Salt treatment (100 mM, 6 days) significantly increased the proline content of shoots but this appeared to be a reaction to stress damage and not associated with salt tolerance, because proline contents were higher in the more sensitive cultivars. Besides proline, some other free amino acids also accumulated leading to a significant increase in the total amino acid content of the stressed seedlings. High levels of free ammonium also accumulated under conditions of stress; this was highly correlated with the accumulation of Na+ in the shoots and negatively correlated with salt tolerance. The accumulation of ammonium was positively correlated with the accumulation of many free amino acids, and also associated with the production of urea in the stressed seedlings. Results from the present investigations suggest that an increase in the concentration of some free amino acids including proline, may be a result of the reassimilation of the stress-induced ammonium. A high capacity to assimilate ammonium may be an important factor in alleviating the consequence of stress because ammonium can be toxic at high concentrations.

Regulation of Ammonium Accumulation during Salt Stress in Rice (Oryza sativa L.) Seedlings

Abstract Metabolic processes related to ammonium release and assimilation were investigated in a salt-sensitive rice (Oryza sativa L.) cultivar Anapurna. Ammonium content of the 3rd leaves increased 3-4 times when seedlings were treated with 100 mM NaCl for 6 days under both growth chamber light condition and in darkness (nonphotorespiration). An in vitro experiment revealed strong inhibition of protein synthesis as an effect of NaCl on the incorporation of 14C-leucine into protein. Exposure to salt stress slightly increased leaf proteolytic activity. The increase of proteolytic activity and decrease of protein synthesis, which directly causes accumulation of free amino acids, might lower the need for ammonium incorporation to form amino acids and indirectly cause the excessive accumulation of ammonium. No significant changes in the assimilatory activities of glutamine synthetase (GS; EC 6.3.1.2) and ferredoxin-dependent glutamate synthase (Fd-GOGAT; EC 1.4.7.1) were found under salt stress. Salt treatment changed the balance of the direction of glutamate dehydrogenase (NAD(H); EC 1.4.1.2); the aminating (NADH-GDH) activity increased while deaminating (NAD-GDH) activity decreased. We conclude that the accumulation of ammonium under salt stress was not due to inhibition of assimilatory activity of GS/GOGAT cycle or aminating GDH. Since these enzymes require supply of C-skeleton in the form of 2-oxoglutarate, reductant and energy to function, the reduction of photosynthetic capacity and the decrease of 2-oxoglutarate might be responsible for the excess accumulation of ammonium in salt-stressed seedlings.

Phytotoxic activity of clomeprop in soil and concentration of its hydrolysed metabolite DMPA in soil water

The relationship between the fate of clomeprop in soil and its phytotoxic activity on the growth of radish (Raphanus sativus) seedlings was investigated in the laboratory. The phytotoxic activity of clomeprop in sea sand was much higher than in non-autoclaved soil, and the phytotoxic activity in non-autoclaved soil was higher than in autoclaved soil. The phytotoxic activity of 2-(2,4-dichloro-3-methylphenoxy)propionic acid (DMPA), a hydrolysed metabolite of clomeprop, was higher than that of the latter under both soil conditions. Clomeprop was adsorbed on soil to a greater extent than DMPA. The concentration of clomeprop in soil water of non-autoclaved soil decreased with increase of the DMPA concentration in the soil water in a time-dependent manner. It is suggested that the phytotoxic activity of clomeprop applied to soil is induced mostly by the DMPA concentration in soil water after hydrolytic degradation by soil microbes.

Adsorption of Herbicidally Active Degradate 2-(2,4-Dichloro-3-methylphenoxy)propanoic Acid on an Andosol

The adsorption of 2-(2,4-dichloro-3-methylphenoxy)propanoic acid (DMPA) on the surface horizon of a humus-rich Andosol was examined. To investigate the mechanisms of adsorption, chemically treated Andosols, such as organic matter removed Andosol, organic matter and active metals removed Andosol, and clay minerals of the Andosol, were prepared. Furthermore, humic acid was extracted from the Andosol. The mechanisms of the DMPA adsorption were identified by using those untreated and chemically treated Andosols and the humic acid. The amount of DMPA adsorbed increased with decreasing equilibrium pH value. Active surface hydroxyl groups were identified as the most important soil functional group in DMPA adsorption. The predominant mechanism of DMPA adsorption on the Andosol is a ligand-exchange reaction, in which an active surface hydroxyl on Al and/or Fe is replaced by a carboxylic group of DMPA. A comparative study revealed that the amount of DMPA adsorbed was slightly greater than that of (2,4-dichlorophenoxy)acetic acid (2,4-D), especially at equilibrium pH values below 5. This is because the octanol-water partition coefficient (log Kow) of DMPA in the equilibrium pH range is higher than that of 2,4-D, and SOM participates in the adsorption process through a hydrophobic interaction.

Mefenaset concentration in the paddy soil and its phytotoxicity to rice plant.

メ フ ェナ セ ッ ト(2-(benzothiazol-2-yloxy) -N -methylacetanilide)は 酸 ア ミ ド系 除草剤 の一 つ で あ る。 著者 らは先 に酸 ア ミ ド系 除草剤 で あ るブ タ ク ロール お よび プ レチ ラク ロール の土壌 中濃度 と稲 に対 す る作 用性 との 関係 につ い て報 告 した3)。 これ ら除 草剤 の土壌 中濃 度 の うち水 可溶 態成分 の 土壌水 分 当た りの濃度 が稲 の 奇形 葉発現 性 と密接 に関係 し てい るこ とが 明 らか にな った。 メ フェナ セ ッ トの水 溶解 度 は0.004g/lで あ る1)。これ はブ タク ロール の 1/5, プ レチ ラク ロール の1/10に 相 当す る。メフ ェ ナ セ ッ トの 土壌 水 分 当た りの 濃度 が前2剤 と同様 に 稲 の奇形 葉発 現性 と密接 に関係 す るこ とを確 か め る た め粒剤 と ともに原体 を供 試 して 実験 を行 い, 2, 3の 知見 を得 た ので その結 果 を報告 す る。

Translocation of naproanilide between mother and daughter plant, and its effect on tuberization of Cyperus serotinus ROTTB.

Naproanilide [2-(2-naphthoxy) propionanilide] translocation between the mother and daughter plants of Cyperus serotinus was investigated in relation to its effect on tuberization.Inhibition of tuberization was found in both plants when naproanilide was simultaneously applied to their underground parts. When applied to the underground part of the mother plant, tuberization was inhibited not only in the mother plant but also in the daughter plant. When treated to the underground part of the largest daughter plant (n-1 plant), naproanilide inhibited tuberization in n-1 plant and in its daughter plants but not in the mother or other daughter plants. The effects of 2-(2-naphthoxy) propionic acid and methyl 2-(2-naphthoxy) propionate, major metabolites of naproanilide, on the tuberization were similar to naproanilide in all treatments.When the underground parts of mother and daughter plants were applied with 14C-naproanilide at the same time, the concentration of radioactivity was higher in the daughter plants. Considerable translocation through the rhizome was found from the mother to the daughter plants but little from the daughter to the mother plant.It is suggested that the inhibition of tuberization in the daughter plant of C. serotinus was caused by the naproanilied and/or its metabolites translocated from the mother plant, and that the small amount translocated from the daughter to the mother plant was the reason the tuberization of mother plant was not inhibited when the herbicide was applied to the daughter plant.

Effects of Temperature on Action, Absorption and Translocation of Simetryne in Rice Plants

32℃ (高温区) と27℃ (中温区) の人工光温室内で栽培した4葉期と6葉期のイネに, シメトリンを施用した場合の生育障害と吸収・移行を比較検討した。1) 土耕栽培で, シメトリン5～20g/aを湛水に処理した場合, 高温区において, また若いイネほど顕著な生育障害が認められた。水耕栽培で, 5～50ppmのシメトリン水溶液に根を浸漬した場合にも同様な結果が得られた。2) 14C-シメトリン (0.6ppm) を含む水耕液に根を6時間浸漬した場合, 4葉期および6葉期のいずれにおいても高温区では中温区の約2倍量のシメトリンが吸収された。根部から茎葉部への移行率には温度の影響が認められないので, 茎葉部中のシメトリン濃度は根による吸収によって律速されると推定された。4葉期と6葉期のイネ茎葉中のシメトリン濃度には差が認められなかった。3) 高温区で生育障害が発生しやすいのは, 根によるシメトリンの吸収量が多くなるためであると考えられる。