Quelques aspects biochimiques de la physiologie des radis (Raphanus sativus L.) traités par la simazine.*

L'action de la simazine ne peut être réduite au seul fait de l'inhibition de la photosynthése. Chez le radis (Raphanus tativus L.). la simazine a provoqué d'abord une baisse considérable du traux des glucides dans le limbe des plantes trailées. Cette diminution a affecté e principalement le glucose et le fructose ct plus encore le saccharose, cependant qu'apparaissait du glycérol. Dans la racine, les osides et les oses ont augmenté pendant les 3 jours qui suivirent le traitement et ont diminué ensuite rapidement. Dans le pétiole, l'évolution a éié intermédiaire. Au stade deux feuilles, les p plantes ayant été misese en lumiére continue aussitôt aprés le traitement, l'augmentation initiale des reserves glucidiques s'est à nouveau produite. Au contraire, dans l'obscurité continue, la diminution des glucides a été analogue chez les plantes témoins et chez les plantes traitées. Quant à la chlorophylle. la teneur a augmenté jusqu'au 4e jour aprés le traitement, puis elle a diminué ensuite en même temps que le saccharose tandis qu'apparaissaient des signes de chlorose. Il est suggéré QUE la disparition du saccharose pourrait provenir, soit d'une inhibition dc sa formation par manque d'ATP photosynthétique-2, soit de son hydrolyse, ce qui expliquerait l'augmentation initiale des oses. Biochemische Cesichispunkle zur Physiologie von Rettichen (Raphanus sativus L.) nach Simazinbekandllug I. Produktion von Gluciden Die Wirkung von Simazin beschränkt sich nicht auf die Hemmung der Photosynthese. In Rettichen (Raphanus sativus L.) verursachte Simazin am Anfang in den Blättern eine beträchtliche Abnahme an Gluciden. Diese Abnahme betraf hauptsáUhlich Glucose und Fructose und noch mehr die Saccharose; dabei trat gleichzeitig Glycerin auf. In den ersten drei Tagen nach der Behandlung nahmen in der Wurzel freie Zucker (Osen) und glykosidisch gebundene Zucker (Oside) zu, danach nahmen sie rasch ab. Im Biatlstiel lag die Produktion dazwischen. Wenn die Pflanzen im 2-Blattstadium unmittelbar nach der Behandlung Dauerlicht ausgesetzt wurden, wiederholte sich die anfängliche Zunahme an ‘glucidartigen’ Reservestoffen. Befanden sich aber die Pflanzen in ständiger Dunkelheit, entsprach die Abnahme an Gluciden der von den Kontrollen. Der Chlorophyllgehalt nahm his zum vierten Tag nach der Behandlung zu und sank dann gleichzeitig mit der Saccharose ab. wobei Anzeichen von Chlorose auftraten. Es liegt die Vermutung nahe, dass die Abnahme der Saccharose entweder mit der Hemmung der Saccharosebildung durch Mangel an ‘Photosynlhcsc-2′-ATP, oder durch ihre Hydrulyse zusammenhánget, was auch die anfängliche Zunahme an Osen erklären würde. Some biochemical aspects of the physiology of radishes (Raphanus sativus L.) treated with simazine I. Production of glucides The action of simazine is not limited to the inhibition of photosynthesis. In radishes (Raphanus sativus L.) simazine caused a considerable initial reduction in the amount of glucides in the leaf blades of treated plants. This reduction applied principally to glucose and fructose and still more to saccharose, while at the same time glycerol appeared. In the root, oses and osides increased over the first 3 days following treatment and then decreased rapidly. In the petiole, production was intermediate. At the two-leaf stage, when the plants were subjected to continuous light immediately after treatment, the initial increase in glucidic reserves was repeated. In continuous darkness, however, the decrease in glucides was similar in both controls and treated plants. The content of chlorophyll increased until the fourth day after treatment then it decreased at the same time as saccharose, while signs of chlorosis appeared. It is suggested that the disappearance of saccharose might be due either to its formation being inhibited through lack of ATP ‘photo-synthetic-2′. or to its hydrolysis, which would explain the initial increase in the oses.     

A bioassay for determining simazine in water using aquatic flowering plants (Ceratophyllum oryzetorum,Ranunculus trichophyllus and Alisma plantago-aquatica)

A simple and rapid bioassay for the measurement of simazine in water using aquatic flowering plants (Ceratophyllum oryzetorum Kom., Ranunculus trichophyllus Chaix. and Alisma plantago-aquatica L.) is reported in this paper. It is based on the effect of simazine on the amount of oxygen produced by photosynthesis which is measured directly using a Clark-type oxygen electrode. This method is rapid, sensitive, and capable of measuring a simazine concentration of 0.02 mg litre^?1 within 10 min of treatment. The precision of this method was examined with spiked river water by comparing the results obtained with HPLC. Mean recoveries of simazine measured by bioassay using C. oryzetorum were 96 to 100% which were comparable to those (98 to 100%) obtained with C18 column extraction and HPLC measurement. The results obtained by the two methods showed excellent agreement. Maintenance of stock cultures of the plants and the bioassay procedure itself were much simpler and more easily conducted than methods using algae.     

The effect of plant-induced changes of pH upon the adsorption and phytotoxicity of s-triazlne herbicides

The effect of plant-induced changes of soluiion pH upon the adsorpiion of s-lriazme herbicides in either K-monimorillonite or Na - bentonite ciay-nutrieni suspensions and iheir phyioioxi- city in soil was studied. ln clay-NO₃^? suspensions (wiih NO₃- as the nitrogen source) maize planls (Zea may L.) caused a marked rise in solution pH and this resulted in a rapid descrp- tion of bound atrazine or simazine. in clay-NHa ⁺ suspensions (with NH4 ⁺ as the nitrogen source) the lowering of solution pH through plant aclivity resulted in jnereased adsorption of these herbicides. In soil, changes of rhizosphere pH were also found when either KNO₃ or (NH₄) ₂SO₄ were supplied as fertilizers, bul it was nol established whether ihis had a direct effeci upon the significant increase in weight of (NH₄)₂SO₄ treated wheat (Tri- ticum aestivum L.) planls at low herbicide concentrations compared with KNO₃ treated wheat plants.     

THE SYNERGISTIC ACTION OF HERBICIDE COMBINATIONS CONTAINING PARAQUAT ON AGROPYRON REPENS (L.) BEAUV.*

Summary. Herbicide combinations containing paraquat were synergistic and provided control of established Agropyron repens (L.) Beauv. (quackgrass) sods for the entire growing season. Paraquat applied at 0–5 lb/ac with simazine or diuron at 4–0 lb/ac was more phytotoxic than either herbicide applied singly and the enhanced activity was more than additive. This synergism was not due to increased absorption or translocation of either herbicide in aerial portions of the plant. Paraquat applied to the shoot increased the susceptibility of quackgrass to simazine action through the soil. Pre-treatment of quackgrass with aminotriazole or amitrole-T at 10 lb/ac 7 days before paraquat application at 0–5 lb/ac provided increased toxicity over that obtained when the two herbicides were applied together or singly. Subsequent studies indicated that aminotriazole applications prior to shoot destruction by either paraquat or clipping resulted in more chronic aminotriazole toxicity. Using methyl-¹⁴C-paraquat it was found that aminotriazole pre-loading also increased the movement of paraquat in and out of the treated leaf. This increase was even more pronounced with amitrole-T. When the two herbicides were applied together, antagonism in absorption and translocation occurred. Action synergique de combinaisons d'herbicides comprenant du paraquat sur Agropyron repens (L.) Beauv.     

Characterisation of a triazine-resistant biotype of Bromus tectorum found in Spain

A population of Bromus tectorum infesting an olive grove at Córdoba (Spain) survived simazine use rates of 3.0 kg a.i. ha⁻¹ over two consecutive years. Non‐tillage olive monoculture and two annual simazine applications had been carried out for 10 years. The resistant biotype showed a higher ED₅₀ value (7.3 kg a.i. ha⁻¹) than that of the susceptible control (0.1 kg a.i. ha⁻¹), a 73‐fold increase in herbicide tolerance. The use of fluorescence, Hill reaction, absorption, translocation and metabolism assays showed that simazine resistance in this biotype was caused by a modification of the herbicide target site, since chloroplasts from the resistant biotype of B. tectorum were more than 300 times less sensitive to simazine than those from the susceptible biotype. In addition, non‐treated resistant plants of B. tectorum displayed a significant reduction in the Q_A to Q_B electron transfer rate when compared with the susceptible biotype, a characteristic that has been linked to several mutations in the protein D1 conferring resistance to PS II inhibiting herbicides. Resistant plants showed cross‐resistance to other groups of triazine herbicides with the hierarchy of resistance level being methoxy‐s‐triazines ≥chloro‐s‐triazines > methylthio‐s‐triazines > cis‐triazines. The results indicate a naturally occurring target‐site point mutation is responsible for conferring resistance to triazine herbicides. This represents the first documented report of target site triazine resistance in this downy brome biotype.     

Influence of nitrogen on competition between cereals and their natural weed populations

The effects of nitrogen fertilizer on the growth and density of natural weed populations in spring barley (Hordeum vulgare L.) and winter wheat (Triticum aestivum L.) were investigated in the absence of herbicide. An increased level of applied nitrogen did not enhance: weed germination, tended to decrease the total weed biomass and had a differential effect upon the biomass of individual weed species in both wheat and barky. In competition with barley, Chenopodium album L. and Lamium spp. had lower nitrogen optima than the crop, while Urtica urens L. had a higher nitrogen optimum. In competition with wheat, Stellaria media (L.) Vill., Lamium spp. and Veronica spp. had lower nitrogen optima than the crop. The systematic changes in nitrogen effect with time were analysed by fitting orthogonal polynomials to the growth and density curves. The methodology could be recommended for other studies in which time or other systematic factors are included, as it supplies information which a traditional analysis of variance cannot provide. Since seed production is positively correlated with biomass, so nitrogen level affects seed production and, hence, the seed pool and future weed population, suggesting that fertilizer usage can be exploited in an integrated programme of crop: weed management. A trend towards lower N fertilizer application owing to concerns about the environment willfavour most of the weed species investigated in these experiments and change the composition of weed populations.     

Interactions between soil-applied herbicides in the roots of some legume species

The effects on plant growth of applying trifluralin or nitralin combination with simazine, atrazine, prometryne and linuron to the upper 5-cm root region of vetch (Vicia sativa L.), pea (Pisum sativum L.) and soybean (Glycine max) were investigated. Foliar injury due to herbicides of the second group was markedly reduced in each species by simultaneous treatment with trifluralin or nitralin both of which inhibited lateral root growth without affecting aerial plant growth or tap root extension growth. This inhibition of lateral root growth in roots treated with trifluralin or nitralin was associated with reduced uptake and subsequent transport to the foliage of ¹⁴C-labelled simazine in vetch and pea and ¹⁴C-labelled atrazine in soybean. This probably accounted for the reduction in simazine and atrazine phytotoxicity. In the presence of trifluralin or nitralin comparatively higher amounts of radioactivity were retained in the roots of pea and soybean and this reduced the amount of ¹⁴C available for transport to the foliage. This was not evident in vetch.     

Mechanisms of resistance to simazine in Sonchus oleraceus

Sonchus oleraceus biotypes resistant to simazine were identified by chlorophyll fluorescence analysis of intact leaves. The mechanisms of resistance were determined on the basis of cpDNA and glutathione S‐transferase (GST) activity analyses. The results of the cpDNA analysis showed that most of the resistant biotypes had a Ser 264 Gly mutation in the psbA gene, which is responsible for an amino acid substitution in the D‐1 protein sequence. The cpDNA fragments were amplified by polymerase chain reaction and digested with restriction enzyme MaeI. Two restriction bands of 338 and 75 bp were recorded in biotypes with the target mutation, while three bands (218, 120 and 75 bp) were present in biotypes without this mutation. A second mechanism of resistance in this species was through the detoxification of simazine by conjugation with glutathione. In resistant biotypes without the above‐mentioned mutation, the average level of GST (simazine) activity in leaves was 4.5‐fold greater than in the resistant biotypes with the target mutation and 8.3‐fold greater than in the susceptible biotypes. Resistance as a result of the target mutation was more common than that achieved through detoxification by glutathione conjugation of simazine.     

Effects of picloram on the synthesis of soluble plant proteins as determined by gel electrophoresis

Changes in soluble proteins synthesized in soybean (Glycine max L.), safflower (Carthamus tinctorius L.), radish (Raphanus sativus L.), and barley (Hordeum vulgare L.) treated with either growth promotive or inhibitory concentrations of picloram (4-amino-3,5,6-trichloropicolinic acid) were determined by polyacrylamide gel electrophoresis and isoelectric focusing. A special gel mixture was developed which provided resolution of protein bands superior to that obtained by standard gel electrophoresis. Growth promotive concentrations of picloram caused both qualitative and quantitative alterations in the band patterns of soluble proteins of safflower, radish, and barley roots and shoots. Isoelectric focusing was applied for the separation and identification of soluble protein fractions from soybean and barley roots and shoots treated primarily with growth inhibitory concentrations of picloram (except for barley shoot tissues). More than 35 clear bands were distinguishable in a typical gel electrophoretogram for either soybean or barley tissue (4-day-old plants). Approximate pI values of the bands from barley root protein were determined from a pH gradient diagram. Protein band patterns of picloram-treated samples were changed qualitatively and quantitatively, in comparison with controls, mostly in the range above pI 6, and predominantly in the neutral and basic protein regions. Band patterns for 96-hr root samples treated with growth inhibitory concentrations of picloram were more similar to those from 48-hr (soybean) or 55-hr (barley) than 96-hr control seedlings. A quantitative decrease in intensity of a band which had the same pI value as that of RNase was noticed in both the treated samples and 2- or 3-day-old control seedlings.     

Weed populations in olive groves under non-tillage and conditions of rapid degradation of simazine

In 49 olive tree groves in southern Spain under non-tillage and treated in the autumn with simazine, a total of 315 weed species was identified. However, only eight annual specics reached a moderate mean infestation of infested ficlds. In each field the number of observed species ranged from 4 to 78. The most important annual species that survived simazine treatment were Lolium rigidum, Galium tricornutum and Sherardia arvensis and, locally in a few fields, others such as Amaranthus spp., Conyza spp., Pulicaria paludosa, Sinapis alba. Torilis arvensis and Rumex bucephalophorus. Sedum album, R. bucephalophorus, P. paludosa, Briza maxima and Hypericum perforatum were mainly found in slope soils with high altitude and low carbon content. Cyperus rotundus, Conyza banariensi, Amaranthus blitoides, Galium spurium and Diplotaxis virgata were found at high densities in irrigated fields. Simazine residues recorded 6 months after herbicide application were very low, amounting on average to levels less than 3% of the applied rate. In soil treated with simazine for 7 years. simazine degradation was much faster than in previously untreated soil, particularly at temperatures of 15-25°C.     

Evolution of resistance to simazine in Senecio vulgaris L.

Fruits were collected from populations of S. vulgaris growing on commercial fruit farms and progenies were tested for susceptibility to simazine. The five least susceptible populations, which originated from sites where simazine had been applied annually for periods ranging from six to ten years, were subjected to two generations of artificial selection for simazine resistance. Two control populations which originated from unsprayed sites were treated similarly. One population originating from Malpas, Cheshire showed a significant response to selection. The simazine resistance of the other six populations was not improved by artificial selection. Selected progenies of the Malpas population were completely unaffected by simazine at 2.8 kg ha^?1. The potential for evolution of resistance to simazine in S. vulgaris is discussed and the effects of ecological and genetic factors on the rate of evolution are assessed.     

Bioefficacy and leaching of controlled-release formulations of triazine herbicides

Conventional formulations of atrazine and simazine were compared with controlled-release formulations of these two herbicides for bioefficacy, leaching and crop safety in laboratory and field experiments. Three light-textured soils with a pH range of 5.8–8.5 were used for this work. An oat bioassay (Avena sativa L.) was used to quantify soil concentrations of the herbicides. Comparison of the initial bioefficacy of controlled-release formulations of atrazine and simazine showed their respective relative potencies to conventional formulations to be 0.51–0.85. The results indicated that the controlled-release formulations maintained an entrapped reserve of active ingredient after delivery with a conventional boomsprayer. In laboratory trials, the controlled-release formulations showed a reduction in leaching compared with conventional formulations. A controlled-release formulation and a conventional formulation of atrazine were tested further in a field trial. A higher concentration of atrazine in topsoil from the controlled-release formulation was observed 11 weeks after application after 107 mm of rainfall. It was deduced that this was caused by reduced leaching of the controlled-release formulation, as observed in laboratory trials. EWRC scores for the control of a range of grass and broad-leaved weeds were identical for both formulations. This indicated that, while the controlled-release formulation could inhibit leaching of the active ingredient, it did not hinder the level of potency necessary for early weed control. EWRC crop safety ratings of chickpeas (Cicer arietinum L.) sown at application were higher for the controlled-release formulation 10 weeks after sowing, and subsequent harvest yields were 50% higher. It was inferred that this resulted from a favourable interaction between crop growth and the timing of the release of the active ingredient from the controlled-release formulation. Altogether, the controlled-release formulations displayed the necessary prerequisites for their further development for large-scale use under arable regimes.     

Cinétique de dissolution dans l'eau de l'atrazine, de la propazine et de la simazine

The kinetics of dissolution of atrazine, propazine and simazine in water The solubaility and kinetics of solubilization of atrazine, propazine and simazine in water were studied at different temperatures. The apparent order of the dissolution reactions is 1 for atrazine and propazine and 2 for simazine. The solubility and rate constants are Increasing functions of the temperature. Activation energies of solubilization are of the order of 41 to 4–8 kcal/mole; they correspond to a 30% decrease in the time of a 50% solubilization when temperature increases by 10°C. It seems therefore that the effectiveness of a treatment can depend in part on the amount of rain and the soil temperature.     

Estimation of thresholds for weed control in Australian cereals

A non-linear model relating crop yield to the density of weeds was fitted to nine Victorian weeds to evaluate their competitive abilities. The weeds were: Acroptilon repens (L.) DC. (creeping knapweed), Chondrilla juncea L. (Skeleton weed, Raphanus raphanistrum L. (Wild radish), lolium rigidum Gaud. (Annual ryegrass), Lithospermum arvense L. (White iron weed), Brassica tournefortii Gouan (Wild turnip), Lamium amplexicaule L. (Deadnettle), Fumaria parviflora Lam. (White fumitory) and Amsinckia hispida (Ruiz & Pav.) I.M. Johnston (Amsinckia). Where more than one experiment was available for a weed, the net return for a herbicide treatment over a range of weed densities was calculated to obtain the economic threshold density. Generally, the economic threshold densities within a weed species were the same order of magnitude, except for the perennial Chondrilla Juncea L., For this species data were collected in years of contrasting rainfall. The model used here is discussed in view of the threshold approach currently used in continental Europe.     

EFFECT OF CHLORTHAL DIMETHYL ON OAT AND FOXTAIL SEEDLING ANATOMY*

Summary. The root and shoot growth of oat (Avena sativa L.) and green foxtail (Setaria viridis (L.) Beauv.) were generally reduced proportionately to the concentration of chlorthal dimethyl applied. Foxtail shoot growth was stimulated by a concentration of 2 ppm. Cells in the shoot and root meristems of treated plants were completely disarranged and considerably hypertrophied. Differentiation was irregular and extended nearer the apices in tissue of treated seedlings than in normal tissue. Histochemical tests showed that the amount of starch, proteins and nucleic acids in seedling tissue decreased with an increase of chlorthal dimethyl concentration, whereas the endosperm of the seeds retained more starch and protein than the controls. The walls of shoot nieristem and root epidermal cells were thickened or altered so as to stain more intensely than corresponding cells in untreated tissue. Effet du diméthyle chlorthal sur l'anatomie des plantules d'avoine et de séaire     

Residues of atrazine, simazine, linuron and diuron after repeated annual applications in a peach orchard

Annual applications of the herbicides atrazine, simazine, linuron and diuron at 45 kg/ha were made to the same plots for 9 consecutive years from 1963 to 1971 in a peach (Prunus persica (L.) Batsch.) orchard located on sandy loam soil near Harrow, Ontario. Soil samples from these plots were collected in late October for the last 3 years (1969–1971) and trees were cut down in December, 1969. Herbicide residues were determined by bioassays based on the fresh and dry weight of oats (Avena sativa L.) and in one year results were confirmed by chemical analysis. Significant accumulation of herbicides was not observed. The maximum residue levels measured in October over the 3 years of sampling were 7′3 kg/ha for diuron, 3–8 kg/ha for linuron, 1–6 kg/ha for simazine and 04 kg/ha for atrazine in the top 15 cm of the soil profile. Simazine and atrazine showed a rapid decrease in amount after treatment but diuron and linuron were degraded more slowly. Measurable residues of all herbicides were confined to the upper 15 cm of the soil profile and the majority of herbicide remained in the 0–5-cm soil layer. Oats were planted in the orchard plots from 1972 to 1974 to follow the disappearance of the herbicides. All herbicides caused highly significant yield decreases in 1972, atrazine causing the least (38%) and diuron the greatest (86%) reductions. Diuron reduced the yield of oats in 1973 and caused a highly significant decrease in the weight of young oat plants in 1974.     

THE EFFECT OF REPEATED FIELD APPLICATIONS OF FOUR HERBICIDES ON THE EVOLUTION OF CARBON DIOXIDE AND MINERALIZATION OF NITROGEN IN SOIL

The effect of repeated annual applications over 7-8 years of MCPA, triallate, simazine and linuron to field plots on the evolution of CO₂ and mineralization of nitrogen in soil samples incubated in the laboratory is described. The plots were either cropped and treated with standard doses, or uncropped and sprayed with doses 3-4 times above the level used in agricultural practice. While the applications of MCPA and tri-allate did not exert any inhibitory effects in soils from the uncropped plots those of simazine and linuron led to a lowering in CO₂ output in several instances and in mineral N on infrequent occasions. These effects are assumed to be the result of a difference in the content of easily-degradable organic matter between the treated plots and the controls. A direct anti-microbial action of the two herbicides is not very probable because in laboratory experiments with simazine up to 512 ppm the output of CO₂ and the mineralization of N was not affected while linuron at 500 ppm gave only a minor depression in CO₂ evolution. Effects on soil fertility are unknown but seem unlikely in view of the small extent and infrequency of the reductions observed. On the cropped plots the MCPA and tri-allate treatment showed no effects. With linuron and simazine a significant lowering in respiration and mineralization of N occurred on single occasions only, during a 5-year period.     

Some effects of the herbicide EL-107 on cellular growth and metabolism

Effects of the herbicide EL-107 (N-[3-(1-ethyl-1-methylpropyl)-5-isoxazolyl]-2,6-dimethoxy-benzamide) on the growth of dicotyledonous plants are described. The herbicide did not inhibit germination but reduced the growth of rape (Brassica napus L.) by half at 0.0057 mg l^?1. The most characteristic symptom induced was a swelling of the apical regions, and histological observations of root tips of Polygonum persicaria and rape revealed a progressve disappearance of the meristematic zone, which was replaced by enlarged cells almost devoid of cytoplasm. Growth of cells of Acer pseudoplatanus L. and soybean (Glycine max L.) cultured in suspension was also inhibited by EL-107, which induced a characteristic change in the cell morphology to an enlarged, rounded shape. EL-107 apparently did not block cell division; at a high concentration it produced some inhibition of protein synthesis, but in Acer cells only. In both types of cell cultures it inhibited, to some extent, the incorporation of glucose into cell wall material.     

Shoot zone uptake of soil-applied herbicides in some legume species

Localized placement of prometryne, linuron and diuron in the soil at the first or second shoot internodes of dwarf broad bean (Vicia faba L.) equally reduced aerial plant growth, whereas simazine and atrazine had no effect. Growth reduction also occurred when the first shoot internode of scarlet runner bean (Phaseolus multiflorus L.) in the soil was treated with all five herbicides, especially with diuron. Localized placement of these herbicides at the first or second shoot internodes of vetch (Vicia sativa L.) in the soil equally reduced aerial plant growth. Foliar injury to vetch due to placement of these herbicides in the shoot zone of the soil was markedly reduced by simultaneous treatment with trifluraiin or nitralin which prevented adventitious root development on the shoot without otherwise affecting plant growth. This lack of root development on the shoots treated with trifluraiin was associated with a marked decrease in ¹⁴C-labelled atrazine uptake, which probably accounted for the reduction in atrazine phytotoxicity. A similar explanation may account for the reduced phytotoxicity of the other herbicides in the presence of trifluraiin or nitralin.