Mode of action of bentazon: Effect on photosynthesis

Bentazon, 3-isopropyl-2,1,3-benzothiadiazin-4-one-2,2-dioxide is effective for weed control in flooded rice fields not only as a foliar treatment but also as a flooded-water or paddy soil treatment. Generally the herbicidal effect develops slowly only after translocation of the herbicide has occurred, but when the weeds contacted directly with relatively high concentrations of the herbicide, the effects appear rather rapid.The slow herbicidal effect appears to be an important mode of action of bentazon applied practically on weeds under flooded rice field conditions. The slow effect may be caused by inhibition of photosynthesis as supported by the following experimental results: a) Bentazon inhibited the Hill reaction in isolated chloroplasts; b) bentazon rapidly inhibited photosynthetic CO₂ fixation in susceptible Cyperus serotinus and other plants; c) the herbicidal effects appeared much slower when bentazon was applied as a flooded-water treatment; d) bentazon injury was prevented by endogenous or exogenously supplied carbohydrates.     

Physiological actions of dinoterb,a phenol derivative: 1. Physiological effects on the whole plant and on tissue fragments of pea

The herbicide dinoterb is a tert.-butyl-2-dinitro-4,6-phenol. Its effects on the metabolism (water, dry matter, nitrogen, chlorophyll, and flavonol contents) were studied on pea plants (Pisum sativum L.). Concurrently, photosynthesis and respiration intensities of treated plants or tissues were measured (O₂ emission or uptake measured on leaf fragments in the reaction vessel of a Clark-type electrode system). Dinoterb, which is an inhibitor of photosynthesis of isolated, physiologically active chloroplasts, also appeared to rapidly inhibit photosynthesis in the whole plant. This property was used for an indirect method of analysis of dinoterb movement in the leaf and in the plant. Dinoterb appears to have a complex mode of action: low concentrations of the herbicide, rapidly appearing in the whole treated leaf, inhibited photosynthesis, uncoupled oxidative phosphorylations, and began to inhibit respiratory oxygen consumption. High concentrations of dinoterb were responsible for important necrosis some days after treatment and we could show, by analysis of the flavonolic accumulation, that cells of the upper epidermis seemed to be first affected.     

The mechanism of bentazon selectivity

Absorption, translocation and metabolism of [¹⁴C]3-isopropyl-2,1,3-benzothiadiazin-4-one-2,2-dioxide (bentazon) by several plant species were investigated to determine the mechanism of bentazon selectivity.Marked selective phytotoxicities were observed between resistant rice (Oryza sativa L.) and susceptible Cyperus serotinus Rottb. when treated with bentazon. Absorption and transolcation of bentazon did not differ greatly between highly resistant rice and susceptible C. serotinus. However, a marked difference in bentazon metabolism occurred between the two species. In rice about 80% of the absorbed bentazon was metabolized within 24 h, and after 7 days about 85% was converted to a major water-soluble metabolite and unchanged bentazon was only 5%. In C. serotinus 50–75% of the radioactivity was unchanged bentazon after 7 days.Large amounts of water-soluble metabolites were detected in root-treated resistant plants such as barnyardgrass (Echinochloa crus-galli Beauv.), soybean (Glycine max Merr.) and corn (Zea mays L.), but only small amounts were present in such susceptible plants as Sagittaria pygmaea Miq. and Eleocharis kuroguwai Ohwi. Therefore, the mechanism of bentazon selectivity appears to be a difference between resistant and susceptible species in their ability to metabolize and detoxify bentazon.The major metabolite in rice was identified as 6-(3-isopropyl-2,1,3-benzothiadiazin-4-one-2,2-dioxide)-O-β-glucopyranoside, determined by GC-MS, NMR, IR and gas chromatography after hydrolysis with sulfuric acid or β-glucosidase.     

The effect of fentin hydroxide (triphenyltin hydroxide) on soybean [Glycine max (L.) Merr.] and rice (Oryza sativa L.) photosynthesis,respiration, and leaf ultrastructure

Soybean [Glycine max (L.) Merr., cv. Swift] plants at the second trifoliate leaf stage and rice (Oryza sativa L. cv. Starbonnet) plants 25 cm tall were treated with 0, 0.56, and 2.24 kg/ha of fentin hydroxide (triphenyltin hydroxide) to determine the effect of this fungicide on photosynthesis, respiration, and leaf ultrastructure. Photosynthesis and respiration were measured with an infrared CO₂ analyzer in an open flow system prior to fentin hydroxide application and at 4, 24, 48, and 96 hr after treatment with fentin hydroxide. No significant detrimental effects on photosynthesis or respiration were evident in either soybean or rice through 96 hr after treatment. Tissue samples from soybean and rice plants, 9 days after fentin hydroxide application, examined for ultrastructure changes with the transmission electron microscope showed no effect due to the fungicide treatment.     

The effect of diflubenzuron [1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea] on soybean [Glycine max (L.) Merr.] photosynthesis,respiration, and leaf ultrastructure

The effect of the insecticide diflubenzuron [1-(4-chlorophenyl)-3-(2,6-difluorobenzoyl)urea] on photosynthesis, respiration, and leaf ultrastructure of soybean [Glycine max (L.) Merr., cv. Swift] was examined on plants treated at the second trifoliate leaf stage with 0, 0.067, and 0.269 kg of active ingredien/ha of diflubenzuron. Photosynthesis and respiration were measured with an infrared CO₂ analyzer in an open flow system prior to diflubenzuron application and at 4, 24, 48, and 96 hr after treatment with diflubenzuron. Diflubenzuron had no effect on soybean photosynthesis at any rate examined. Respiration was stimulated by the high rate (0.269 kg/ha) in a transitory manner. Tissue samples removed from both old and new leaves, 9 days after diflubenzuron application, were used for the ultrastructure study with the transmission electron microscope. The lower trifoliate leaves contained more starch grains than the upper ones being formed after treatment, but no aberrations or degradation of leaf ultrastructure due to diflubenzuron treatment were evident.     

Herbicidal interference with the photochemical activities of chloroplasts (in vivo and in vitro) of certain crop and weed species

The independent modes of action of diuron and atrazine on the photochemical activities of chloroplasts (In vivo and in vitro) from the leaves of crop plants Pisum sativum and Pennisetum typhoides and the weeds Amaranthus viridis and Cyperus rotundus were investigated. Hill reaction activity (DCPIP photoreduction) of in vivo chloroplasts (chloroplasts isolated from herbicide-sprayed plants) was unaffected by treatment at sublethal or intermediate levels of diuron or atrazine while that of in vitro chloroplasts (chloroplasts incubated in the required herbicidal concentration) was severely inhibited. The ferricyanide catalyzed noncyclic photophosphorylation was markedly reduced in both the in vivo and in vitro chloroplast systems. N-Methyl phenozonium sulfate (PMS)-mediated cyclic photophosphorylation was inhibited in the in vivo system while a pronounced enhancement of activity was noticed in the in vitro chloroplasts. The rate of NADP⁺ photoreduction was severely inhibited in the in vitro chloroplasts. The unaffected in the in vivo system. The herbicidal effects on the photoreactions of isolated chloroplasts were compared with chloroplasts isolated from herbicide-sprayed plants.     

Physiological basis of bentazon tolerance in rice (Oryza sativa L.) lines

In the present study, 98.8 mm of bentazon was applied to 3‐leaf stage rice seedlings. Two tolerant lines, M202 and cv. TNG67, showed slightly visible injury, photosystem II inhibition, as well as a low level of lipid peroxidation 7 days after application compared with the susceptible lines. Further physiological study of the mechanism of differential tolerance among Japonica and Indica types indicated that, although the tolerant Japonica lines M202 and cv. TNG67 absorbed more ¹⁴C‐bentazon, most of the ¹⁴C remained in the treated leaf or translocated to older leaves. However, two susceptible lines, FSK (Japonica) and IR36 (Indica), absorbed less ¹⁴C‐bentazon throughout the experiment, and most of the ¹⁴C was translocated from the treated leaves to younger leaves, which might result in the death of developing tissues. In addition, more bentazon residue and less polar metabolites were detected in these two susceptible lines. It is proposed that the higher tolerance of lines M202 and TNG67 to bentazon could be mainly due to a higher rate of metabolism of this herbicide, and partially due to less translocation to developing tissues.     

Effects of dimethazone (FMC 57020) on chloroplast development: 1. Ultrastructural effects in cowpea (Vigna unguiculata L.) primary leaves

The effects of dimethazone [FMC 57020; 2-(2-chlorophenyl)methyl-4,4-dimethyl-3-isoxalidinone] on the growth and ultrastructure of cowpea (Vigna unguiculata L.) were examined. Seeds were imbibed in 0.5 mM dimethazone for 1 day and grown for 4 to 5 subsequent days in darkness without the herbicide. The herbicide stunted etiolated hypocotyl growth and retarded greening under 150 μmol · m⁻² · sec⁻¹ white light. No effects of dimethazone on the in vivo absorption spectrum of the etiolated primary leaf was detected. The herbicide caused some reduction and disorganization of prothylakoids in etiplasts. After 3 hr of white light chlorophyll accumulation was greatly reduced in treated leaves and ultrastructural development of the chloroplasts of herbicide-treated tissues appeared to be retarded. Pronounced thylakoid disruption was noticed in some cells after 12 hr, was more common after 24 hr, and was found in all cells by 72 hr. Maximally affected plastids lacked thylakoids, had irregular envelopes, and contained numerous vesicles.     

Glyphosate toxicity in the shoot apical region of the tomato plant: I. Plastid swelling is the initial ultrastructural feature following in vivo inhibition of 5-enolpyruvylshikimic acid 3-phosphate synthase

Glyphosate induces swelling and eventual bursting of the plastids in the young tissue of the shoot apical region of tomato plants. This rapid and specific effect parallels the concentration of glyphosate in the tissues and the degree of in vivo inhibition of 5-enolpyruvylshikimic acid 3-phosphate synthase as measured by the accumulation of shikimic acid and shikimic acid 3-phosphate. The chloroplasts of the young apical leaves begin to swell between 16 and 20 hr after treatment of the plants with a sublethal glyphosate dose and burst after 4 days. Glyphosate-induced swelling of the proplastids begins much later (at 2 days) in the apical meristem itself than in the apical leaves. The meristem recovers 5 days after glyphosate treatment because the cells containing the damaged proplastids become displaced toward the rib meristem according to the inherent pattern of cell division.     

FACTORS AFFECTING THE PHYTOTOXICITY OF PARAQUAT*

Summary. Temperatures of 5–6° C delayed leaf necrosis of glasshouse-grown oats (Avena sativa), winter peas (Pisum sativum), huisache (Acacia farnesiana), mesquite (Prosopis julijiora var. glandutosa), live oak (Quercus virginiana) and yaupon (Ilex vomitoria) for at least 48 hr after treatment with paraquat as compared with higher temperatures. After 96 hr, oats, winter peas, huisache and mesquite at 5° C usually showed as much necrosis as plants at 24–28° C. Similar results were obtained with live oak and yaupon, and with yaupon in the field, except that longer periods were sometimes required for plants at low temperatures to develop injury comparable with that at higher temperatures. Washing yaupon and live oak leaves 1 hr after application reduced the effectiveness of paraquat regardless of temperature, but washing winter peas 10 min after application had little or no effect on phytotoxicity. Field-grown mesquite showed extensive leaf necrosis when leaves were washed after 20 min, live oak leaves similarly treated and washed were not injured, while the response of winged elm (Ulmus alata) was intermediate. Percentage leaf necrosis of mesquite, winged elm, yaupon and live oak increased with increasing paraquat concentration; 6–9 μg/leaf on mesquite and 20 μg/leaf on winged elm gave 100% necrosis after 4 days. Complete leaf necrosis of live oak and yaupon was not attained during this period even with 80 μg/Ieaf. Nursery-grown mesquite, yaupon and greenbriar (Smilax bona-nox) and natural stands of yaupon were treated at two growth stages, in March and May. Paraquat was more effective on mesquite when applied in May, but there were no differences with the other species. Facteurs affectant la toxicité du paraquat     

Interference of herbicides with photochemical activities of chloroplasts in six shrub species

The effects of paraquat and 2,4,5-T on the photochemical activities of chloroplasts from the leaves of the woody species Carissa spinarum, Maba buxifolia, Flacourtia sepiaria, Chomelia asiatica, Gymnosporia emarginata and Dodonaea viscosa were investigated by comparing the effects on isolated chloroplasts from untreated leaves with those on chloroplasts isolated from herbicide-sprayed plants. DCPIP and NADP reduction of chloroplasts incubated in paraquat or 2,4,5-T solution was inhibited, whereas that of chloroplasts isolated from most species sprayed with these herbicides was enhanced after 24 and 48 h. The enhancement was smaller or disappeared after 72 h. The cyclic and noncyclic photophosphorylation rates were suppressed in chloroplasts isolated from herbicide-treated plants, and also in those from most untreated plants incubated in the herbicide solutions. The differences in reactions of chloroplasts from herbicide-treated and untreated plants are discussed.     

Effect of Figaren, an Antiviral Protein from Cucumis figarei, on Cucumber mosaic virus Infection

Local lesion formation on cowpea leaves was more than 50% inhibited by treatment with a 23 kDa RNase-like glycoprotein from Cucumis figarei, figaren, from 24 hr before to 1 hr after inoculation with Cucumber mosaic virus (CMV). CMV accumulation detected by ELISA in tobacco leaves treated with figaren 6 or 0 hr before inoculation with CMV was suppressed. When upper leaves of tobacco plants were treated with figaren and inoculated 10 min later with CMV, mosaic symptoms were delayed for 5–7 days on most of the tobacco plants, and some plants remained asymptomatic. From fluorescence in situ hybridization, infection sites were present in figaren-treated cowpea or melon leaves after inoculation with CMV, though the sites were reduced in number and size compared with those in water-treated control leaves. The amount of CMV RNAs and CMV antigen in melon protoplasts inoculated with CMV and subsequently incubated with figaren similarly increased with time as did that in the control. ELISA and local lesion assays indicated that CMV infection on the upper surfaces of the leaves of tobacco, melon, cowpea and C. amaranticolor whose lower surfaces had been treated with figaren 5–10 min before CMV inoculation was almost completely inhibited. Figaren did not inhibit CMV infection on the opposite untreated leaf halves of melon, cowpea and C. amaranticolor, whereas it almost completely inhibited CMV infection on the untreated halves of leaves of tobacco. CMV infection was not inhibited in the untreated upper or lower leaves of the four plants. These data suggest that figaren does not completely prevent CMV invasion but does inhibit the initial infection processes. It may also induce localized acquired resistance in host plants. Received 10 October 2000/ Accepted in revised form 6 February 2001     

百合无症病毒对百合光合生理、酶活性及叶绿体超微结构的影响

 以东方百合“西伯利亚”为试验材料,研究百合无症病毒(LSV)侵染百合对其叶片生理生化以及叶绿体超微结构的影响。检测结果表明:叶片中叶绿素a、b以及总叶绿素含量与健康对照相比分别下降了28.6%、33.3%和23.5%,净光合速率、气孔导度及胞间CO₂浓度分别下降33.3%、25%和13.8%;超氧化物歧化酶(SOD)、过氧化物酶(POD)、多酚氧化酶(PPO)和苯丙氨酸解氨酶(PAL)与健康对照相比,分别增加了16.6%、29.4%、16.7%和22.2%。电镜观察发现:感病植株叶绿体膨胀变形,基质片层散乱,叶绿体内淀粉粒肿大且数目增多,从而证明LSV侵染破坏叶绿体结构,影响植株的光合作用。     

Diquat enhancement of cupric ion toxicity

Cupric ion inhibition of Chlorella growth and photosynthesis and electron transport in isolated chloroplasts was enhanced by concentrations of diquat (6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium) that did not inhibit these processes in the absence of cupric ions. Diquat decreased the lag in cupric ion inhibition of Chlorella photosynthesis from 5 to 3.3 min. Diquat enhancement of cupric ion toxicity was immediate with no lag when diquat was added to Chlorella cells with photosynthesis inhibited by cupric ions. Diquat was absorbed by isolated chloroplasts with an intact outer envelope and the absorption was not due to diquat binding to chloroplast membranes. Cupric ion movement through the outer envelope of chloroplasts was stimulated by the presence of diquat. Cupric ion toxicity was also increased by diquat in bicarbonate solutions. The optimum molar ratios of cupric ions to diquat among those tested for diquat enhancement of cupric ion toxicity were 1:0.188 and 1:0.2, which are 1:1 and 1:1.08 on a parts per million basis.     

Mode of action of meturine

The effect of meturine on the light processes of photosynthesis was studied.Meturine is a herbicide for weed control in potato and cotton crops. It is a N-phenyl—N-hydroxy—N′-methylurea.The experiments were carried out on isolated pea and spinach chloroplasts.When examining photosystem I, reduced DPIP was used as an electron donor, whereas methyl-viologen served as an electron acceptor. When examining photosystem II, DPIP represented the electron acceptor.The obtained experimental results have pointed to the absence of the effect of meturine upon the photoreaction I.Unlike N-phenyl—N′, N′-dimethylureas (CMU, DCMU) meturine has been a very weak inhibitor of photoreaction II.The authors explain the photoreaction II inhibition of chloroplasts from plants treated with herbicidal doses of meturine by conversion of N-phenyl—N-hydroxy—N′-methylurea into Hill reaction inhibitor(s). N-Phenyl—N′-methylurea can be one of such meturine metabolites.Meturine herbicidal action is accounted for by meturine transformation into Hill reaction inhibitor(s) in the plant tissues.     

Effects of dimethazone (FMC 57020) on chloroplast development: II. Pigment synthesis and photosynthetic function in cowpea (Vigna unguiculata L.) primary leaves

The herbicidal action of dimethazone [FMC 57020; 2-(2-chlorophenyl) methyl-4,4-dimethyl-3-isoxalidinone] on cowpea (Vigna unguiculata L.) primary leaves was studied. Seeds were imbibed in 0.5 mM herbicide for 1 day and then seedlings were grown in darkness. In 6-day-old, etiolated seedlings, there was no effect of the herbicide on protochlorophyllide accumulation or on phototransformation of protochlorophyllide to chlorophyllide, however, the Shibata shift was greatly slowed. Accompanying this was a delay in phytylation of chlorophyllide. Protochlorophyllide resynthesis in a dark period after phototransformation of existing protochlorophyllide in etiolated tissue was also slowed by dimethazone. In the light, carotenoid accumulation and chlorophyll accumulation were slowed by the herbicide, resulting a pale green appearance of the leaves. The capacity for CO₂-dependent oxygen evolution or FeCN-dependent oxygen evolution did not develop in dimethazone-treated tissue during 24 hr of light exposure. In situ measurement of variable fluorescence and cytochrome f photooxidation/dark reduction indicated that some cyclic electron transport developed very slowly in dimethazone-treated plants. No effect of the herbicide was found on either FeCN-dependent oxygen evolution or variable fluorescence in fully greened tissues. Dimethazone was concluded to have an effect on chloroplast development rather than a direct effect on photosynthesis.     

Salicylic acid alleviates growth inhibition and oxidative stress caused by zucchini yellow mosaic virus infection in Cucurbita pepo leaves

The effects of zucchini yellow mosaic virus (ZYMV) infection and pretreatments with salicylic acid (SA) on biomass accumulation of pumpkin (Cucurbita pepo cv. Eskandarani) were investigated. The response of photosynthesis, transpiration and the activities of antioxidant enzymes in leaves was also considered. Significant reductions in growth parameters (i.e. leaf area, biomass and shoot height), photosynthesis and chlorophyll a and b content were detected in ZYMV-infected leaves in comparison to healthy controls. Antioxidant enzyme activities were increased up to 3-fold for peroxidase (POD), 2-fold for ascorbate peroxidase (APX) and catalase (CAT) activities and 1.3-fold for SOD activity by virus infection. ZYMV infection also caused increases in H₂O₂ and malondialdehyde (MDA) contents. These results suggest that ZYMV infection causes oxidative stress in pumpkin leaves leading to the development of epidemiological symptoms. Interestingly, spraying pumpkin leaves with SA led to recovery from the undesirable effects of ZYMV infection. Leaves treated with 100 μM SA three days before inoculation had the appearance of healthy leaves. No distinct disease symptoms were observed on the leaves treated with 100 μM SA followed by inoculation with ZYMV. In non-infected plants, SA application increased activities of POD and superoxide dismutase (SOD) and inhibited APX and CAT activities.In contrast, SA treatment followed by ZYMV inoculation stimulated SOD activity and inhibited activities of POD, APX and CAT. In addition, MDA displayed an inverse relation, indicating inhibition of lipid peroxidation in cells under SA treatment. It is suggested that the role of SA in inducing plant defense mechanisms against ZYMV infection might have occurred through the SA-antioxidant system. Such interference might occur through inhibition or activation of some antioxidant enzymes, reduction of lipid peroxidation and induction of H₂O₂ accumulation following SA application.     

Saflufenacil absorption and translocation in winter wheat (Triticum aestivum L.)

Research was conducted to determine the mechanism(s) responsible for safening winter wheat to postemergence-applied saflufenacil when mixed with 2,4-D amine or bentazon. Less than 10% of applied saflufenacil was absorbed when mixed with bentazon whereas absorption peaked at 16% at 14 days after treatment when saflufenacil was applied alone. Wheat plants absorbed 2.8- to 3.5-times more saflufenacil when saflufenacil was applied with 2,4-D amine compared to saflufenacil alone. Regardless of herbicide treatment and harvest timing, <10% of absorbed saflufenacil was translocated from the treated leaf to other plant parts. Safening of saflufenacil with bentazon is likely due to reduced absorption of saflufenacil into winter wheat plants. In the presence of crop oil concentrate, saflufenacil absorption was enhanced by 2,4-D amine. The influence of bentazon and 2,4-D amine on saflufenacil absorption in wheat plants likely explains the differences in wheat response observed in previous research.     

Systemic infection of some N-gene-carrying Nicotiana species and cultivars after inoculation with tobacco mosaic virus

Since July 1974Nicotiana tabacum ‘Samsun NN’ plants, inoculated with the common strain of tobacco mosaic virus (TMV), have occasionally been found to develop necrosis on non-inoculated upper leaves 2–7 days after the local necrotic lesions had appeared on the lower leaves. All these plants had been kept in a growth chamber at 17–20°C. Other tobacco species and cultivars carrying theN gene, such asN. glutinosa andN. tabacum ‘Xanthi-nc’, showed the same phenomenon. Substantial amounts of TMV could be recovered from leaves with systemic symptoms. The systemic necrosis somewhat resembled that caused by tobacco rattle virus (TRV). A number of possible causes, such as high concentration of the inoculum, contamination with another strain of TMV or with TRV, change in the genetic composition of the host plants and certain growing conditions (soil, water, pesticides) were investigated. None of these factors could be held fully responsible for the abnormal systemic reaction, although there was evidence that the soil could sometimes play an important rôle.     

苹果链格孢菌侵染对感病苹果品种叶细胞超微结构的影响

 将Alternaria mali分生孢子接种在苹果元帅品种叶片的下表皮,保湿培养3~24h,观察细胞超微结构,接种后3h,表皮及叶肉细胞的质膜发生内陷,出现囊泡,暗染色颗粒及管状结构,叶绿体膜结构解体,电子致密物质沉积,基粒排列混乱松散,外膜破裂等。接种后24h,叶片表面出现病斑,细胞质浓缩,细胞壁出现颗粒物,细胞变形,病健组织交界处,叶绿体基浓缩,出现脂质球,同时还观察到,距离病斑2mm处,许多叶肉细胞中出现密度均匀、形状不规则的物质,小叶脉木质部中出现电子致密物质沉积。