Studies were carried out to develop a new bio-assay method for evaluating the effects of chemicals on root elongation. In the procedure, a polyethylene disc 5cm in diameter and 0.3cm thick on which germinated plant seeds had been placed was floated on water in the presence or absence of chemicals (Fig. 1); and subsequently the root elongation was observed.
The results obtained are as follows:
(1) Rice plant (cv. Akinishiki) was found to be the most suitable species for the bioassay among 7 gramineous plants tested, since the species showed a uniform growth and the fasted elongation of seminal roots in water (Fig. 2).
(2) Growth of the rice seminal roots was markedly affected by the changes in the light and temperature conditions. It was demonstrated that incubation in the dark at 30°C was optimum to secure uniform and rapid elongation of the roots (Tables 1 and 2).
(3) Maximum elongation rate (3.8cm/day) of the roots was obtained on the third day of the incubation (Fig. 3).
(4) Effects of organic solvents, surfactants and a carrier of herbicidal wettable powder on the elongation of the roots were investigated by adopting the new method under the conditions, previously descrived. Ethanol and the carrier did not inhibit the elongation of the rice seminal roots at concentrations ranging from 0.1 to 300ppm (w/w) (Fig. 4).
(5) The elongation of the rice seminal roots cultured by the new method was compared to that of roots cultured in water in a petri-dish. It was evident that the former roots grew faster than the latter without twisting, hence evaluating precise measurements of the root length (Fig. 5 and Photo 1).
(6) Effect of pretilachlor [2-chloro-2′, 6′-diethyl-N-(2-propoxyethyl) acetanilide] on the elongation of the rice seminal root and safening effects of CGA-123, 407 [4, 6-dichloro-2-phenylpyridine] as well as NA on the herbicide could be clearly evaluated through this bioassay method (Fig. 6 and Fig. 7).
The result obtained suggest that this method could be applied for investigating the herbicidal action of chemicals on root elongation.

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Effect of application of butachlor [N-butoxymethyl-α-chloro-2′, 6′-diethylacetanilide], pretilachlor [α-chloro-2′, 6′-diethyl-N-(2-propoxyethyl) acetanilide] and NSK-850 [α-chloro-N-(3-methoxy-2-thienyl) methyl-2′, 6′-dimethylacetanilide] herbicides on the growth of transplanted rice (cv. Akinishiki, 2 leaf stage) cultivated at different depths (1, 4 and 8cm) of flooding water was examined by pot tests in a greenhouse. Inhibitory effect on plant height and dry weight of shoots of rice plants by butachlor (15g/a), pretilachlor (10g/a) and NSK-850 (5g/a) decreased with the increase of the depth of the flooding water (Fig. 1). These results could not be explained by the difference in herbicide sensitivity of rice plants in relation to the changes in the depth of flooding water, because rice plants grew taller, the dry weight of their shoots decreased and thus they were likely to be come more sensitive to herbicides with the increase of the depth of flooding water (Fig. 2). Therefore, it was suggested that other factors such as the role of the plant parts related to the absorption of the herbicides and behavior of the herbicides in soil and water were mainly involved in the above-mentioned phenomena.
Plant parts related to the absorption of butachlor, pretilachlor and NSK-850 were examined by application of the chemicals to leaf blades, shoots (basal parts) and roots of rice plants. Since the chemicals inhibited the growth of rice plants most strongly by root application, it was concluded that these herbicides were absorbed mainly through roots in rice plants (Fig. 3).
Time course of butachlor, pretilachlor and NSK-850 concentrations in flooding water and soil was monitored by HPLC analyses during 300hr following the treatment. In all cases, the concentrations of the herbicides in flooding water decreased with the increase of the depth of flooding water, and reached maximum values shortly after treatment. Similar results were obtained for the concentrations of the herbicides in soil, but maximum values were observed later than in the case of flooding water.
The results obtained suggested that the depth of flooding water affected the rice phytotoxicity of these α-chloroacetanilide herbicides, i. e. butachlor, pretilachlor and NSK-850. This assumption was based on the fact that since the herbicide concentrations in water and soil in the vicinity of the main parts of the plant related to the absorption of the chemicals increased shortly after application when the depth of flooding water decreased, a larger amount of the chemicals was likely to be absorbed.

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The activity of the peroxidase (POD) and superoxide dismutase (SOD) isozymes in paraquat resistant and susceptible biotypes of E. philadelphicus was examined in the presence or absence of paraquat application.
Results obtained are as follows:
1. When examined by agar gel thin layer electrophoresis, the bands of POD isozymes separated from the resistant and susceptible biotypes were different and exhibited different activities (No. 1 and 2) (Fig. 1).
2. When examined by polyacrylamide gel electrophoresis (PAGE), the activities of the bands of the POD isozymes were generally weak in the susceptible biotype in the case of paraquat application. In the resistant biotype, a new band was observed near the No. 6 band, and its appearance and activities changes during the 32 day period extending from the onset to the end of paraquat application (Fig. 2).
3. When examined by isoelectric focusing electrophoresis (IEF), the activity of band (a) of the POD isozymes was high in the susceptible biotype, while that of band (c) was high in the resistant biotype. In the susceptible biotype, the activities of bands (a) and (b) increased by paraquat application, whereas those of the band group (d) decreased with the duration of the application period. In the resistant biotype, the activities of the band group (d) also decreased with the duration of paraquat application, but to a lesser extent than in the susceptible biotype. There were no marked differences in the decreasing activities of band (c) (Fig. 3 and 4).
4. The above-mentioned results suggested that the properties of the POD isozymes were that some different between the resistant and susceptible biotypes and may be modified by paraquat application.
5. Two bands of SOD isozymes were detected in both biotypes by horizontal agar gel thin layer electrophoresis, and 4 bands by the PAGE method (Fig. 5 and 6). However, the position and activities of these bands in the electrophoresis did not appear to be affected by paraquat application.

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Concentrations of acetanilide herbicides, butachlor (2.5% granule) and pretilachlor (2.0% granule) in paddy soils were evaluated in relation to their phytotoxicity to rice plant (CV. Musashikogane), using Yawara and Ryugasaki paddy soils with different properties. The results obtained are as follows:
1. The amount of acetone-soluble ingredients of butachlor and pretilachlor in the Yawara and Ryugasaki paddy soils (0-1cm) was reduced to 10-25% of the initial dose, after 10 days of herbicide application. Residual ratio of the two herbicides showed the same trend, but was slightly higher in the Ryugasaki soil, Most of the ingredients were localized in the 0-1cm layer of the soils.
2. The ratio of the water-soluble ingredients to the acetone-soluble ones in the soil was found to be 30%, on the day of herbicide application, except for butachlor in the Yawara soil. The butachlor ratio in the Yawara soil was 15%. The amount of butachlor soluble in water after 3, 5 and 10 days of application was found to be 21, 8 and 15% in the Yawara soil and 25, 15 and 14% in the Ryugasaki soil. On the other hand, the ratio of water-soluble pretilachlor in the two soils types ranged from 5 to 8.5% 3 days after herbicide application.
3. The percentages of rice plants injured by the herbicides were higher in the Ryugasaki soil than in the Yawara soil. Phytotoxicity to rice plant of butachlor or pretilachlor was closely related to the concentrations of the water-soluble ingredients in the soil. These findings suggest that the phytotoxicity to rice plant of acetanilide herbicides depends on the concentration of water-soluble herbicides which is affected by the soil properties.

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Pendimethalin (N-(1-ethylpropyl)-2, 6-dinitro-3, 4-xylidine), was applied to a paddy field (paddy-uplandcrop-rotation field) in Yawara and a field in Kannondai planted to winter wheat and the concentration of the acetone soluble and the water soluble ingredients in the soil was determined. The concentrations of the water soluble ingredients of pendimethalin in soil was also determined in relation to the effect on the growth of Italian ryegrass (CV. WASEAOBA) in the soil treated with the herbicide.
The results obtained are as follows;
1. The concentration of the residues of the acetone soluble ingredients of pendimethalin applied to the soil decreased with time. However, the amount of the residues after 200 days of application fluctuated in the field treated with the herbicide. The concentration of the water solubleingredients in the soil to which the herbicide had been applied (emulsifiable concentrate and fine granules) decreased so rapidly that there was a close correlation between the concentrations and the number of days after herbicide treatment (Fig. 1 and Fig. 2).
2. In the plowed soil of the Yawara field, the ratio of the concentration of the water soluble ingredients to that of the acetone soluble ingredients in the soil treated with the emulsifiable concentrate (30%, 150g a. i./10a) was 4-8% on the day of application, about 2-3% after 60 or 90 days and less than 2% after 90 or 120 days. In the non-plowed field, the corresponding values of the ratio were 3-5% after 60 or 90 days of application and about 1% after 90 days. In the case of the plowed field to which fine granules of pendimethalin had been applied (2.0%, 100g a. i./10a), the values of ratio were about 2% on the day of application, 8-10% after 30 days, 3-5% after 60 or 90 days, less than 2% after 120 days. The values of the ratio in the non-plowed field were 2-3% from the day of application to 90 days after, and less than 0.5% after 120 days of application. In the soil at KANNONDAI field to which fine granules of pendimethalin had been applied (2.0%, 80g and 160g a. i./10a) the value of ratio was the highest, 15% after 30 and/or 60 days of application. The value of the ratio remained at about 10% even after 120 days (Table 3 and Table 4).
3. The soil from the field to which pendimethalin had been applied was periodically collected. There was a significant correlation between the concentration of the water soluble ingredients in the soil water and the growth inhibition of Italian ryegrass. These findings suggested that the activity of pendimethalin in the soil depended on the concentration of the water soluble ingredients in the soil water (Fig. 3 and Fig. 4).

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CMP, DMPA and 2, 4-D at 10^-5M concentration affected the leaf angle of radish seedlings. In root application, DMPA and 2, 4-D provided a more remarkable effect than CMP, but in shoot application, CMP was most effective in hormonal effect.
¹⁴C-CMP was absorbed by radish seedlings to a greater extent than ¹⁴C-DMPA. Root applied ¹⁴C-DMPA translocated well to shoots and remained there in higher amount than that of metabolite DMPA derived from root applied ¹⁴C-CMP.
In shoot application, ¹⁴C-DMPA was slightly absorbed by shoots of radish, whereas ¹⁴C-CMP absorption was very high. Also, the metabolite DMPA was detected in high concentration in shoots. These findings might explain the difference in hormonal activity of CMP and DMPA when applied to roots or shoots of radish seedlings.

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Herbicidal activity of picloram (4-amino-3, 5, 6-tricloropicolinic acid) on sabmha Eupatorium adenophorum SPRENG. was found to increase with the addition of ammonium sulfate or 2, 4-D [(2, 4-diclorophenoxy) acetic acid] to the spray solution. Ammonium sulfate, especially, a notable synergistic effect with picloram on growth of E. adenophorum plants.
Ammonium sulfate increased absorption of the ¹⁴C-picloram into the plants 3 to 6 times more than picloram alone, while 2, 4-D was not found to affect the absorption, translocation or metabolism of picloram in E. adenophorum.
It is concluded that ammonium sulfate enhances the picloram herbicidal activity by increasing the latter's absorption; the enhancing mechanism of 2, 4-D remains to be clarified. The interaction of 2, 4-D and picloram at the action site in plants should be studied.

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To construct a growth and competition model of D. adscendens and soybean, we analysed the temporal changes in the dry matter partitioning ratio and specific leaf area (SLA) of both species as a function of the developmental stage (DVS) of each species. The data of this study were obtained from field experiments in which the D. adscendens community was cultivated in mixed stand with soybean (cv. Enrei) at various sowing dates or planting densities of soybean for four consecutive years as compared with the “Enrei” soybean community in pure stand (Table 1).
Developmental stage (DVS) of both species was deduced from the DVS model (Formulas (1) and (2)). In D. adscendens, DVS was 0 at the onset of emergence, 1 at heading and 2 at ripening. In soybean, DVS was 0 at the onset of sowing, 1 at flowering and 2 at ripening. DVS of both species which was predicted using previous models and data (Fig. 1, 2 and Formulas (1)-(7)) showed a good fit to the values observed in field experiments (Table 2).
In both species, the dry matter partitioning ratios for each plant organ changed with the developmental stage (DVS) and they were not appreciably affected by other factors, such as, year of experiment, sowing date and planting density (Fig. 4). Therefore, it appeared that the temporal in the dry matter partitioning ratio of both species could be represented using the Table function in which DVS is an independent variable and the dry matter partitioning ratios are dependent variables (Formulas (8), (9) and Table 3).
In the pure stand soybean, the SLA changed with the DVS and was not appreciably affected by other factors. However in D. adscendens under soybean culture conditions, the temporal changes in SLA were affected by the DVS and also by the shading of soybean leaves. Then, it was considered that to represent the degree of shading by the soybean leaves by Q=(plant height of soybean/plant height of D. adscendens)×(LAI of soybean) and to adjust the data using Q of each DVS, the temporal changes in SLA of D. adscendens in mixed stand with soybean could be represented by the Table function in which DVS is the independent variable and SLA the dependent variable (Tables 4, 5 and Fig. 5).

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Glasshouse experiments were conducted to investigate effects of plant age and other factors affecting the contact of pretilachlor [2-chloro-2′, 6′-diethyl-N-(2-propoxyethyl)-acetanilide] with plants on the herbicidal activity against rice (Oryza sativa L. cv. Nihonbare) and Echinochloa oryzicola VASING..
The pretilachlor activity on seeded rice was higher when rice was shallowly seeded than when seeded deeply, and its activity on rice seeded shallowly decreased more sharply than that on Echinochloa as leaf stage at application developed (Figs. 1 and 2). Seeding depth did not affect the activity on Echinochloa at all (Fig. 2), which depended only on leaf stage at the time of pretilachlor application (Figs. 1 and 2).
Shallow planting (Table 1) and water percolation (Table 2) intensified the phytotoxicity of pretilachlor on transplanted rice, which was not affected by water depth (Table 3). Neither water depth nor water percolation affected the pretilachlor activity on Echinochloa at all (Tables 4 and 5).
Pretilachlor applied only to the soil surface was selective between rice and Echinochloa seeded at 15mm depth; applied to the position of seed or root, however, the chemical was not selective (Figs. 3 and 4).
The role of soil treatment was dominant in the activity of the overall treatment (combination of soil and foliar treatments) on the grasses, and that of foliar treatment was negligible in rice and slight in Echinochloa when pretilachlor was applied at about the 2 leaf stage of the plants (Fig. 5).
The following conclusions were therefore drawn:
1) The primary bases for the selectivity of pretilachlor between transplanted rice and Echinochloa are difference in availability of the chemical to the site of uptake and difference in plant age:
2) physiological difference in the response to pretilachlor additionally contributes to the selectivity:
3) the pretilachlor activity on the grasses greatly depends on the degree of its contact with the coleoptilar node: and
4) the contact of pretilachlor with the foliar does not play any role in its phytotoxicity on the rice crop.

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A sesquiterpene ketoalcohol, cyperolone, was isolated from nutsedge essential oil, and its inhibition of the growth of rice and lettuce seedlings was investigated. Cyperolone was a stronger inhibitor than sesquiterpene ketones such as cyperotundone and α-cyperone. Cyperolone completely inhibited the growth of lettuce seedlings at the concentration of 4.2×10^-3M, at which it did not inhibit the germination of lettuce seeds. Accordingly, cyperolone-related compounds were synthesized to study the mode of the inhibitory action, and were tested plant bioassays. The diol, dione and trione derivatives inhibited growth less than the cyperolone and sesquiterpene ketones. Dihydrocyperolone was strongly inhibitory. These results suggested that the inhibitory effect of cyperolone may be due to the C-3 hydroxyl and C-4 carbonyl in its structure.

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NAC (1-naphthyl methylcarbamate), a carbamate insecticide, at 10^-3M concentration reduced the herbicidal activity of clomeprop [2-(2, 4-dichloro-3-methylphenoxy) propionanilide, CMP] when applied simultaneously with CMP or 1 or 3hr before CMP application. Hormonal activity of CMP was also reduced by NAC simultaneously applied to shoots of radish, while DMPA activity was not affected by NAC.
In a metabolism study, NAC was found to reduce DMPA production by CMP in radish seedlings, indicating an inhibitory action of NAC on CMP metabolism to DMPA. When CMP was applied together with NAC, CMP showed much lower herbicidal and hormonal activities, so that DMPA was assumed to be the active compound of the herbicide clomeprop in plants.

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In June, 1986, 15ha of corn fields at Nasu in Tochigi pref. were found to be infested with yellow nutsedge (Cyperus esculentus L.). The weed seemed to be propagated from seeds which had contaminated packed hay imported from the United State. Since the propagation density and the plant height of the weed were larger than those of purple nutsedge (C. rotundus L.).
The growth of the crop was markedly inhibited. This study carried out oralyse the ecological and physiological characteristics of the weed, yellow nutsedge. Result obtained are as follows.
1) Yellow nutsedge grown in Nasu area was indentified as C. esculentus var. leptostachyus based on the inflorescence pattern, plant type and the shape of the tubers.
2) In the pot test, two mother tubers of purple and yellow nutsedge produced 16-26 and 100-120 tubers in a year, respectively.
The mean weight of a tuber was 1.26g in the former and 0.12g in the latter. The maximum plant height of yellow nutsedge was 107.4cm which was almost 5 fold that of purple nutsedge, 21.5cm.
3) Although number of tubers formed decreased with the increase of the depth of the position of the mother tubers in soil, the weed was able to propagate from the tubers planted at a 28cm depth in soil.
4) Cutting of the above ground parts of the weed, or 2cm from the basal position and at different growth stage affected tuber formation which was markedly reduced by cutting when the plant height was 40cm.

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