Differential effects of phenoxy herbicides on light-dependent CO2 fixation in isolated cells of C3 and C4 plants

Cells were isolated from the developing leaves of Ipomoea aquatica and Digitaria sanguinalis. The effects of phenoxy alkanoic acid herbicides on light-dependent ¹⁴CO₂ fixation and oxygen evolution in these leaf cells were studied. (2,4-Dichlorophenoxy)acetic acid and (2,4,5-trichlorophenoxy) acetic acid (2,4,5-T and 2,4-D) caused a 20% stimulation of ¹⁴CO₂ fixation at 0.8 × 10⁻⁵M and an inhibition at 1 × 10⁻⁴M in I. aquatica leaf cells. Temperature seemed to have a marked influence on such action. No effect or very little effect was observed in the leaf cells of D. sanguinalis. The nonactive (2,4,6-Trichlorophenoxy)acetic acid (2,4,6-T) caused a similar stimulation of CO₂ fixation as 2,4-D and 2,4,5-T at low concentrations in I. aquatica leaf cells, but no inhibition was observed at high concentration. Increase of hight intensity increased the rate of CO₂ fixation in both control and 2,4,6-T-treated cells; however, the percentage of stimulation remained the same. At stimulatory concentration, all three compounds did not cause any stimulation in either photosystem I and II or photosystem II-mediated oxygen evolution. At higher concentrations, the differential effects of 2,4-D and 2,4,5-T on the light-induced CO₂ fixation and photosystem II-mediated oxygen evolution in the I. aquatica leaf cells and D. sanguinalis mesophyll (ms) cells may be attributed in part to their selective action against dicotyledonous plants.     

Influence of monuron on photosystem II and light-dependent 14CO2 fixation in isolated cells of C3 and C4 plants

Cells were isolated from the developing leaves of Ipomoea aquatica (water spinach), a C₃ plant, and three kinds of C₄ plants, namely, Digitaria sanguinalis (NADP⁺-specific malate dehydrogenase type), Panicum miliaceum (NAD⁺-specific malic enzyme type), and Panicum texanum (phosphoenopyruvate carboxy kinase type), to study the effect of monuron on light-dependent ¹⁴CO₂ fixation and oxygen evolution. Bundle sheath cells, except for those of D. sanguinalis, and mesophyll cells of all plants fixed approximately the same amount of ¹⁴CO₂. Monuron, at the range used (2 to 10 × 10^?7M), showed strong inhibition in the mesophyll cells of water spinach and in bundle sheath cells of P. miliaceum and P. texanum and moderate inhibition in the mesophyll cells of all C₄ plants. In the bundle sheath cells of D. sanguinalis the low rate of ¹⁴CO₂ fixation was stimulated to some extent by the addition of malate and ribose 5-phosphate. The I₅₀ value was 6 × 10^?7M for the sensitive cells. Monuron inhibited the oxygen evolution of all seven cell types and their I₅₀ values varied between 3 × 10^?7 to 6 × 10^?7M. The differential response of isolated plant cells from different species to light-dependent CO₂ fixation in the presence of monuron may also be involved in urea herbicide selectivity and undoubtedly is due to the differential photosynthetic pathways present nn them.     

Soil persistence experiments with [14C]2,4-D in herbicidal mixtures, and field persistence studies with tri-allate and trifluralin both singly and combined

The persistence of [¹⁴C]2,4-D at a rate equivalent to 1 kg/ha was studied in the laboratory on a heavy clay and a sandy loam at 85%of field capacity and 20°C both alone and in the presence of 1 kg/ha dicamba, dichlorprop, difenzoquat, TCA, and 2,4,5-T. The persistence of 2,4,5-T was also monitored in both soils under the same conditions in the presence and absence of [¹⁴C]2,4-D. All soils were extracted at weekly intervals using aqueous acidic acetonitrile and analysed for [¹⁴C]2,4-D remainining radiochemical techniques. The extracts containing 2,4.5-T were additionally analysed gas chromatographically for that herbicide. In each soil type the half-life of the 2,4-D was similar regardless of whether applied singly or in combination with the five herbicides tested. Similarly, [¹⁴C]2,4-D did not affect the breakdown of 2,4,5-T in either soil type. The persistence of tri-allate (1·5 kg/ha) and trifluralin (0·75 kg/ha) both singly and in combination were compared using small field plots at two locations in Saskatchewan. Applications were made during May of 1977 and 1978 and the plots were sampled and analysed for herbicide(s) remaining after 10 and 20 weeks, respectively. The results indicate that within experimental error the loss of both tri-allate and trifluralin from the plots treated with the mixture was the same as from plots treated with the individual compounds.     

Relative persistence of di-and tri-chlorophenoxyalkanoic acid herbicides in Saskatchewan soils

The persistence of 2,4-D, 2,4-DB, dichlorprop, 2,4,5-T, and fenoprop at the 2 ppm level was studied in the laboratory on three prairie soils at 85% of field capacity and 20°C. Following extraction of the soils with aqueous acetonitrile containing acetic acid, the herbicidal acids remaining were analysed gas chromatographically. Breakdown was rapid on all soils and the average half-lives for 2,4-D, 2,4-DB, dichloroprop, 2,4,5-T, and fenoprop were < 7, < 7, 10, 12, and 12 days respectively. Degradation on air-dried soils (15% of field capacity) was negligible with over 85% of the applied herbicides being recoverable after incubation periods during which the herbicides remaining in the moist soils accounted for less than 30% of the original treatments. Persistance relative des acides di et tri-chlorophénoxy-alkanoï-ques herbicides dans des sols du Saskatchewan. La persistance du 2,4-D, du 2,4-DB, du dichlorprop, du 2,4,5-T et du fénoprop, à la concentration de 2 ppm, a étéétudiée au laboratorire, sur trois sols de prairie, a 85% de la capacité au champ et a 20°C. Après leur extraction des sols par l'acétonitrile aqueux contenant de l'acide acétique, les acides herbicides restants ont été analysés par chromatographie en phase gaseuse. La dégradation a été rapide pour tous les sols et les demi-vies moyennes du 2,4-D, du 2,4-DB, du dichlorprop, du 2,4,5-T, et du fénoprop ont été respectivement de <7, <7, 10, 12 et 12 jours. La dégradation sur des sols séchés a l'air (15% de la capacité au champ), a été négligeable, plus de 85% des quantités d'herbicides appliquées étant récupérables après des périodes d'incubation durant lesquelles les herbicides restant dans les sols humides ne représentaient plus que moins de 30% des quantités apportées à l'origine. Relative Persistenz von Di-und Trichlorphenoxyalkansäure-Her-biziden in Böden Saskatchewan In Laborversuchen wurde die Persistenz von 2,4-D, 2,4-DB, Dichlorprop, 2,4,5-T und Fenoprop in drei Prärieböden festgestellt. Die Versuche wurden bei 20°C, 85 % der Feldkapazität und einem anfänglichen Herbizidgehalt der Böden von 2 ppm durchgeführt. Die Extraktion der Böden erfolgte mit wässerigem Acetonitril mit einem geringen Anteil an Essigsäure. Die Herbizide wurden gaschromatographisch nachgewiesen. In allen Böden wurde ein schneller Abbau festgestellt. Die Halbwertszeiten betrugen für 2,4-D, 2,4-DB, Dichlorprop, 2,4,5-T und Fenoprop < 7, < 7,10, 12 bzw. 12Tage. Der Abbau im lufttrockenen Boden (15% der Feldkapazität) war zu vernachlässigen. Hier waren noch mehr als 85% der ausgebrachten Herbizidmenge vorhanden, wenn in den feuchten Böden die Konzentration bereits weniger als 30% betrug.     

Plant growth substance action on lecithin and lecithin/cholesterol vesicles

The adsorption of some plant growth regulating compounds onto lecithin and equimolar lecithin/cholesterol vesicles and the effect of these substances on the rate of chloride/nitrate and sodium/potassium ion exchange across the vesicular membranes have been examined. On comparing the binding of 2,4-D, 2,6-D, 2,4,5-T and IAA to lecithin vesicles in solution at various pH values it is found that the unionised form of these acids is bound very much more strongly than the ionised form. Compounds having relatively low oil/water partition coefficients such as 2,4-D, 2,6-D and 2,4,5-T are adsorbed onto vesicles, from solutions containing equimolar equilibrium concentrations of the unionised molecules, to markedly different extents (depending on the structure of the lipophilic portion of these molecules). Where the oil/water partition coefficient is higher, as for 2,4-dichlorophenol and 2-(2,4-dichlorophenoxy)ethanol, binding to vesicles may also arise due to non-specific solution within the hydrocarbon region of the lipid bilayers. The affinity of these compounds for lecithin has also been assessed by noting the extent to which the inclusion of lecithin in the oil phase increases the oil/water partition coefficient. This has shown that affinity for lecithin depends on the structure of both the lipophilic and hydrophilic portions of the molecule. Only the unionised form of the compounds examined had any large effect on ion flux across the vesicle membranes. Significant increases in the rate of chloride/nitrate exchange were obtained on introducing quite high concentrations (0.015 to 1.5 mM) of the compounds 2,4-D, 2,6-D, 2,4,5-T, IAA, and 2,4-dichlorophenol, but not 2,4-dichlorophenoxyethanol, to suspensions of lecithin vesicles. Similar flux increases were observed with lecithin/cholesterol vesicles except that more pronounced effects on flux were obtained on adding 2,4-dichlorophenol and 2,4-dichlorophenoxyethanol. In contrast 2,4-D, 2,6-D, 2,4-dichlorophenol and IAA had no significant effect on the rate of Na⁺/K⁺ ion exchange across lecithin vesicles although increases were observed with equimolar lecithin/cholesterol vesicles. Interpretations of these phenomena are suggested and their relevance to plant growth substance effects at the plasmalemma membrane discussed.     

Effect of some herbicides on CO2 fixation,intermediates pattern,and ruDP-carboxylase and FDPase activities of spinach chloroplasts

We have studied the inhibitory effect of the herbicides phenmediphan, chloroxuron, dinoseb, dichlobenil, dicamba, 2,4-D, 2,4-DB, and 2,4-DP on photosynthetic CO₂ fixation and on the level of intermediates of the CO₂ assimilation cycle by isolated chloroplasts, as well as their in vitro activities on the enzymatic systems ribulose-1,5-diphosphate carboxylase and fructose-1,6-bisphosphatase. Phenmedipham showed the strongest inhibition of CO₂ assimilation, with an I₅₀ of 0.05 μM, followed by chloroxuron and dinoseb, with a 50% inhibition in the range of 0.5–1 μM. A weaker inhibitory effect, with an I₅₀ of 50 μM, is promoted by 2,4-DB, whereas dicamba and 2,4-DP showed this inhibition at 100 μM; dichlobenil and 2,4-D were completely ineffective. In the presence of phenmedipham and chloroxuron, the $\text{trioses-}\text{P}\text{P}\text{-glycerate}$ ratio showed a sharp decrease, which means an inhibition of the P-glycerate reduction step by a low NADPH synthesis; a low ratio is also promoted by 2,4-D, but it may be a consequence of induced collateral metabolic pathways of P-glycerate. Dinoseb showed a 25% inhibition of ribulose-1,5-diphosphate carboxylase activity in the concentration range of 10–100 μM and an I₅₀ of 50 μM of the fructose-1,6-bisphosphatase. Thus these effects could contribute, in addition to the photochemical ones, to an explanation of the dinoseb inhibition of CO₂ assimilation by isolated chloroplasts. The other herbicides tested showed a weak or no effect on these enzyme systems.     

Cuticular penetration of 2,4-D as affected by interaction between a diethylene glycol monooleate surfactant and apple leaf cuticles

Impacts of pH and sorption-desorption of ‘Pegosperse’ 100-O (PEG. 100-O; diethylene glycol monooleate, containing 15% diester) surfactant by apple (Malus pumila M.) leaf cuticles on surfactant-enhanced cuticular penetration of 2,4-D [(2,4-dichlorophenoxy)acetic acid] were studied. Glass cylinders were affixed to enzymatically isolated adaxial apple leaf cuticles after the cuticle segments had been soaked in 10 ml liter^?1 PEG 100-O solution and washed for 20 and 120 min, respectively. Quantities of [¹⁴C]2,4-D in the glass-cuticle chambers passing through the cuticles at pH values from 1 to 6 5 were determined. PEG 100-O significantly increased cuticular penetration of dissociated 2,4-D at pH 4–5; the surfactant had no effect on penetration of undissociated 2,4-D at pH 10. Surfactant-enhanced penetration of 2,4-D occurred only when the surfactant was in the cuticles, while the process of surfactant sorption-desorption alone had no effect on penetration. These results support a ‘hydrophilic channel’ hypothesis, i.e. that surfactants may create hydrophilic channels or increase the area of the channels in the cuticle and, consequently, enhance the passing of polar molecules like dissociated 2,4-D through the cuticle.     

Mixtures of picloram and 2,4,5-T for the control of blackberry (Rubus fruticosus L. agg.)

The effectiveness of‘Tordon 50-d’(5% a.i. picloram plus 20% a.i. 2,4-D both as the triisopropanolamine salts) and various mixtures of 2,4,5-T and picloram were tested for the control of blackberry (Rubus fruticosus L. agg.) in Victoria, Australia. A high correlation was obtained between the % reduction in live canes and the % kill of crowns 13 months after Rubus procerus P.J. Muell. thickets were sprayed with 2,4,5-T or‘Tordon 50-d'. Counting the number of live canes is, therefore, a convenient method of comparing the efficacy of these herbicides for the control of blackberry. ‘Tordon 50-d’was generally more effective than 2,4,5-T but stimulation of suckering from roots was recorded at one site when low rates of‘Tordon 50-d’were used. It was necessary to add high dose rates of‘Tordon 50-d’to 2,4,5-T before there were worthwhile improvements in weed control.‘Tordon 5–20’(5% a.i. picloram as triisopropanolamine salt plus 20% 2,4,5-T as the ethyl hexyl ester) was only slightly more effective in controlling blackberry than‘Tordon 50-d'. The cost and soil residue problems associated with picloram should limit its use as an additive to 2,4,5-T for the control of blackberry in Australia.     

The effect of herbicides on respiration and transformation of nitrogen in two soils III. Lenacil, terbacil, chlorthiamid and 2,4,5-T

The effects of lenacil, terbacil, chlorthiamid and 2,4,5-T at 100 ppm on carbon dioxide evolution, oxygen uptake and nitrogen transformation in two soils have been investigated for several months in the laboratory. The herbicides had no effect on CO₂ output from either Boddington Barn soil (organic carbon content 1.6%, pH 6.1) or Triangle soil (organic carbon content 3.7%, pH 4.8) apart from 2,4,5-T which reduced it sometimes. All the herbicides caused temporary reductions in O₂. uptake, but in Triangle soil treated with 2,4,5-T a significant reduction was observed during the second half of the incubation. 2,4,5-T and to a lesser extent chlorthiamid, reduced nitrification in Triangle soil. All the herbicides slightly increased mineralization of nitrogen except 2,4,5-T which had variable effects in Triangle soil.     

THE METABOLISM OF A SERIES OF CHLOROPHEN-OXYALKYL ACID HERBICIDES IN BIGLEAF MAPL. E,ACER MACROPHYLLUM PURSH.*

Summary. Studies of the metabolism characteristics of 2,4-D, 2,4,5-T, dichlorprop and fenoprop were made to gain a better understanding of the differential response of a woody Plant, big leaf maPl. e, to certain phenoxy-type herbicides. In one test in which detached leaves were used, it was established that decarboxylation is not an important detoxification mechanism in treated foliage. This same test showed the phenoxyacetic herbicides to be more stable than the α-phenoxypropionic herbicides in treated leaves. In intact Plants 2,4,5-T was consistently more stable than 2,4-D, but the relative amount of metabolism of the herbicides varied with the Plant part. The results are discussed with respect to the differential response of bigleaf maPl. e. Métabolisme d'une série d'herbicides du groupe des acides chlorophénoxyalkylés dans l'érable à grandes feuilles Acer macrophyllum Pursh.     

A review of foliar absorption and translocation of 2,4-D and 2,4,5-T

This review is restricted to an examination of the literature on the environmental and chemical factors that affect foliar absorption and translocation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichloro-phenoxyacetic acid (2,4,5-T) by plants. Most of the papers covered by this review have been published since 1965. Earlier works have been reviewed elsewhere by other authors (Currier & Dybing, 1959; Sargent, 1965; Franke, 1967; Robertson & Kirkwood, 1969; Hull, 1970). Often absorption and translocation of herbicides are considered together; here the two will be considered separately wherever possible.     

Erythrocyte membrane protein damage by phenoxyacetic herbicides and their metabolites

In the present work, we describe the effect of chlorophenoxyl herbicides 2,4-dichlorophenoxyacetic acid (2,4-D), 4-chloro-2-methylphenoxyacetic acid, and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and their metabolites (2,4-dichlorophenol, 4-chloro-2-methylphenol, 2,4-dimethylphenol, and 2,4,5-trichlorophenol) on the activity of ATPase and the corresponding protein damage (measured by loss of -SH group). Basic compounds caused an increase in the activity of the enzyme by 7-9% (at concentration 1 mM). For higher concentrations (2 and 4 mM), a decrease in the ATPase activity was observed for all investigated compounds. The increase of the free -SH group content was observed for all compounds. More profound changes in investigated parameter values were observed for metabolites (when compared to basic compounds) which may suggest their higher toxicity.     

Herbicide and inhibitor effects on cell leakage in suspension cultures of tobacco (Nicotiana tabacum)

Effects of selected herbicides and respiratory inhibitors on leakage from tobacco (Nicotiana tabacum) cell suspension cultures were studied. Leakage was monitored by quantitation of fluorescein dye released from preloaded cells and by measuring conductivity changes in the suspension medium. The herbicides ioxynil, Barban, 2,4,5-T, MCPB, and PCP (10^?6 to 10^?4M) caused leakage of fluorescein dye and electrolytes within 2 hr of exposure to the herbicides. Potassium cyanide and 2,4-DNP caused appreciable leakage at the same concentrations. Similar responses were induced by anaerobiosis. Atrazine, metolachlor, paraquat, and nitrofen did not induce leakage when tested at concentrations of 10^?6 to 10^?4M.     

Residues in blackcurrants,fodder peas,spinach and potatoes treated with sublethal doses of 2,4,5-T to simulate wind drift damage

Blackcurrants, treated with 0.1 kg of 2,4,5-T ha^?1 (as esters of mixed C₄–C₆ alcohols; ‘Tormona 80’), contained 0.1 mg of 2,4,5-T residues kg^?1 in the berries at ripeness 29 days after treatment. Total residues in the berries were not reduced during growth and ripening, although the residue concentrations declined in the same period due to growth dilution. In spinach leaves from old plants, treated with 0.1 kg ha^?1, 0.05 mg of 2,4,5-T kg^?1 was found 14 days after treatment. Fodder peas showed no residues (< 0.002 mg kg^?1) at harvest 62 days after treatment with 2,4,5-T esters. After application of 0.1 kg ha^?1 on potato plants, the disappearance of 2,4,5-T was rapid during the first month, but residues were translocated into the tubers and reached a constant level of 0.02 mg kg^?1 after 1 month until harvest at 108 days after treatment. In all crops, visible effects were observed after treatment with 0.1 kg ha^?1. After the application at 0.01 kg ha^?1, phytotoxic effects were observed only in blackcurrants, but negligible residues were found in all the test crops.     

Effect of plant growth regulators on the shoot gall formation in mango caused by Apsylla cistellata Buckton (Psyllidae: Homoptera) in India

Abstract

Trials were conducted from 1979 to 1983 at Pantnagar on the effect of 2,4‐dichlorophenoxy acetic acid (2,4‐D) (5 to 250 mg/litre), 2,4,5‐trichloroxyphenoxy acetic acid (2,4,5‐T) (5 to 250 mg/litre), 1‐naphthyl acetic acid (NAA) (5 to 500 mg/litre), chlorocholine chloride (CCC) (50,100 mg/litre), naleic hydrazide (MH) (50, 100 mg/litre), abscisic acid (10, 50 mg/litre), gibbrellic acid and Alar (10 and 50 mg/litre) on the gall formation in mango by Apsylla cistellata Guckton. There was no effect on the number of galls formed but abnormal, open, elongated galls were formed in the case of 2,4‐D (100 mg/litre and above) and 2,4,5‐T (150 mg/litre), in which nymphs of A. cistellata could not survive, resulting in control of the pest. No flower panicles emerged on the twigs with no nymphal population.     

Spray application factors and plant growth regulator performance: II. Foliar uptake of gibberellic acid and 2,4-D

Effects of droplet size and carrier volume on foliar uptake and translocation of gibberellic acid (GA₃) and 2,4-D were investigated. Simulated spray droplets were applied to primary leaves of 10-day-old Phaseolus vulgaris (cv Nerina) in droplet sizes and carrier volumes ranging from 0.5 to 10 μl and 10 to 200 μl per leaf, respectively. Doses of GA₃ (2 μg per leaf) and 2,4-D (100 μg per leaf) were held constant. Total uptake of GA₃ approached a penetration equilibrium within 24 h after application, but uptake of 2,4-D continued to increase. Decreasing droplet size and/or increasing carrier volume increased GA₃ and 2,4-D uptake. Translocation to stem and roots was positively related to total uptake. A positive linear relationship between the logarithm of the total droplet/leaf surface interface area and 2,4-D uptake or translocation was found, but for GA₃ this relationship was quadratic. Potential mechanisms of the effects of spray application factors on foliar uptake are discussed. © 1999 Society of Chemical Industry     

Effect of 2,4,5-T and picloram on the regeneration of blackberry (Rubus procerus P.J. Muell) from root segments

The formation of roots and shoots on root segments of Rubus procerus P.J. Muell was prevented by soaking the segments for 24 h in a 10^?4M solution of 2,4,5-T or a 10^?5M solution of picloram. Shoot numbers were significantly increased after treatment with 10^?9M and 10^?10M 2,4,5-T, but picloram did not cause a significant increase in shoot numbers. Measurement of the concentration of 2,4,5-T in the extracambial tissue showed that roots treated with 10^?4M 2,4,5-T contained 5× 10^?8 mmole 2,4,5-T per mg dry weight, and by extrapolation, roots treated with 10^?9M 2,4,5-T contained 2× 10^?10 mmole/mg dry weight. Action du 2,4,5-T et du piclorame sur la régénération de la ronce (Rubus procerus P.J. Muell) è partir de fragments de racines La formation de racines et de tiges è partir de fragments de racines dc Ruhus procerus P.J. Muell a été supprimée par trempage des fragmenls pendant 24 heures dans une solution a 10^?4M et de 2.4,5-T, ou dans une solution 10^?5M de piclorame. Le nombre de pousses s'est accru significativement après traitement avec le 2,4,5.-T è 10^?9M et 10^?10M, mais le piclorame n'a pas provoqué d'accroissemcnt significatif du nombre de pousses. La mesure de la concentration de 2,4,5-T dans le tissu extra-cambial a montré que les racines trailées avec du 2,4,5-T è 10^?4M contenaient 5×10^?8 mmole de 2.4,5-T par mg de poids sec et par extrapolation, quc les racines traitées avec du 2,4,5-T k 10^?9M devaient contenir 2 × 10^?12 mmole/mg de poids sec. Die Wirkiing von 2,4,5-T und Picloram auf den Wuchs der Wurzehegmenten von Bromheeren (Rubus procerus P.J. Muell). Die Bildung von Wurzeln und Sprossen aus Wurzelsegmen-ten von Ruhu.i procerus P.J. Muell wurde durch 24-stündiges Einlegen der Wurzelstücke in 10^?4M 2,4,5-T bzw 10^?5M Picloram verhindert. Die Anzahl neugebiideter Sprosse wurde nach Einlegen in 10^?9M und 10^?10M 2,4,5-T, nicht jedoch durch Picloram, signifikant erhöht. Im extracambialen Gewebe von Wurzeln, die mit 10^?4M 2,4,5-T behand-elt worden waren, wurden 5×10^?8mMol 2,4,5-T je mg Trockengewiclu bestimmt. Durch Extrapolation wurde ermittclt. dass mit 10^?9M 2,4,5-T behandelte Wurzeln 2× 10^?12mMol/mg Trockengewicht cnthielten.     

Growth, photosynthetic pigments and photosynthetic activity during seedling stage of cowpea (Vigna unguiculata) in response to UV-B and dimethoate

UV-B (0.4 W m⁻²) irradiation and dimethoate (100 and 200 ppm) treatments, singly and in combination, declined the growth, photosynthetic pigment contents and photosynthesis (O₂ evolution and CO₂-fixation) of cowpea (Vigna unguiculata). Contrary to this, low concentration of dimethoate (50 ppm) caused stimulation on these parameters, while together with UV-B it showed inhibitory effects. Carotenoids (Car) showed varied responses. It was found that carbon-fixation (¹⁴CO₂) was more sensitive to both the stresses than photosynthetic oxygen evolution. Photosynthetic electron transport activity was reduced by both the stresses, however, 50 ppm dimethoate besides inhibiting photosystem II (PSII) and whole chain activity, showed slight stimulation in photosystem I (PSI) activity. The individual effect of two stresses on PSII activity was probably due to interruption of electron flow at oxidation side of PSII which extended to its reaction center following simultaneous exposure. A similar trend was also noticed in case of CO₂ liberation (measured as ¹⁴CO₂ release) in light and dark. Results suggest that dimethoate (100 and 200 ppm) and UV-B alone caused heavy damage on pigments and photosynthetic activity of cowpea, leading to the significant inhibition in growth. Further, the interactive effects of both the stresses got intensified. However, low concentration (50 ppm) of dimethoate showed stimulation, but in combination, it slightly recovered from the damaging effect, caused by UV-B.     

The hydrolysis of herbicidal phenoxyalkanoic esters to phenoxyalkanoic acids in Saskatchewan soils

The hydrolysis of the iso-propyl, n-butyl-and iso-octyl esters of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), the n-bytyl ester of 2,4-dichlorophenoxybutyric acid (2,4-DB) and the iso-octyl ester of 2,4-dichlorophenoxypropionic acid (2,4-DP) was studied in four prairie soils of differing textures and pH at 25±1°C. The esters were analysed using gas chromatography. After 24 h in soils at wilting point moisture, and above, less than 20% of the applied iso-propyl and n-butyl esters could be recovered from one soil type and none from the remaining three. Loss of the iso-cotyl esters was slower; however, no trace of the 2,4,5-T and 2,4-DP esters was observed in any of the moist soils after 48 and 72 h respectively. In all cases loss of all esters from air-dried soils minimal. The phenoxyalkanoic acid hydrolysis products were recovered from all soil types, treated with the various esters and identified using thin-layer chromatography.     

2,4-Dichlorophenoxyacetic acid (2,4-D) and paranitrophenol (PNP) interactions with gills of Anodonta californiensis and Mytilus californianus: Uptake and effects on membrane fluxes

The effects of pesticides and their breakdown products on membrane fluxes is a subject of interest in assessing the potential ecological impact of these substances. As part of a continuing program we have examined the effects of 2,4-dichlorophenoxyacetic acid (2,4-D) and paranitrophenol (PNP) on divalent cation and primary amine losses from and glycine uptake by gills of the bivalve molluscs Anodonta californiensis (fresh water) and Mytilus californianus (marine). Both 2,4-D and PNP reduce glycine influx into gills of M. californianus. This observation is consistent with the view that glycine is bound to the gill surface as a Mg²⁺ complex prior to active transport.For gills of A. californiensis, Ca²⁺ and Mg²⁺ losses are increased by 10^?3M 2,4-D relative to that into distilled water. Primary amine losses are increased for both A. californiensis and M. californianus gills at low 2,4-D concentrations.For A. californiensis and M. californianus gills the uptake of both 2,4-D and PNP are reduced by increasing concentrations of Ca²⁺ and Mg²⁺. In the case of A. californiensis, Ca²⁺ has a larger effect than Mg²⁺, which is consistent with the demonstrated stabilizing effect of Ca²⁺ on biological membranes. The uptake of PNP is larger than that of 2,4-D and glycine for gills of A. californiensis. The uptake of 2,4-D is reduced by the presence of an excess concentration of glycine but this is probably a physical effect. The uptake of 2,4-D, PNP, and glycine are all passive processes for A. californiensis gills. Glycine does not reduce 2,4-D uptake into M. californianus gills. For M. californianus the transport mechanism for glycine is not the same as that for 2,4-D; the former being active transport and the latter passive transport. However, 2,4-D does interfer with the active transport of glycine.