Photosynthetic inhibition in Phaseolus vulgaris II. The influence of light on herbicidal action

The influence of pre-treatment and post-treatment illumination upon the herbicidal effect produced in Phaseolus vulgaris L. cv. Berna by simeton, diuron, diquat and ioxynil was examined. The increased effect noted at lower pre-treatment and higher post-treatment levels of illumination was correlated with increased inhibition of net photosynthesis. This increased effect was ascribed to enhanced photo-oxidation.     

AN ASSEMBLY FOR THE CONTINUOUS RECORDING OF CO2 EXCHANGE AND TRANSPIRATION OF WHOLE PLANTS

Summary. Photosynthesis, respiration and transpiration of whole platns are continuously recorded with the assembly described. An infra-red gas analyser is used for photosynthesis and respiration measurements, while for transpiration data psychrometers are employed, Air and leaf temperatures as well as light intensity are recorded. The assimilation chamber is constructed in such a way that whole platns of various plant species can be investigated under constant conditions of CO₂ content of the air and air humidity. Some experiments with simazine and monuron are described.
Un appareil pour enregistrer continuellement l'échange de CO₂ et la transpiration des plantes entiéres     

SELECTIVITY AND PHYSIOLOGICAL INACTIVATION OF SOME HERBICIDES INHIBITING PHOTOSYNTHESIS

Summary. The effects of several herbicides on the rates of CO₂ uptake and transpiration of intact plants were measured. A simple technique is described which reveals whether photosynthesis-inhibiting herbicides are inactivated by plants. By this method, the inactivation of simazine by maize could be confirmed. Evidence is presented for physiological inactivation of monuron by Plantago lanceolata , of cycluron (OMU) and pyrazon by sugar beet, of N'-(4-butoxyphenyl)-NN-dimethylurea by of 5-bromo-6-methyl-3-phenyluracil by flax. Certain plant species showed different reactions to some other new herbicides. The effect of herbicides in the culture solution on CO₂ uptake by the leaves is probably largely determined by the rate of transpiration of the plants. Assuming that uptake in proportional to transpiration rate, estimates of the concentration of the herbicides inside the plant were made.
L'inactivation physiologique de quelques herbicides produisant une inhibition de la photosynthèse     

EFFECT OF TRANSPIRATION RATE OF BEAN PLANTS ON INHIBITION OF PHOTOSYNTHESIS BY SOME ROOT-APPLIED HERBICIDES

Summary. The inhibition of photosynthesis of bean plants (Phaseolus vulgaris L.) by root-applied herbicides was determined at different rates of transpiration, obtained by varying air humidity, light intensity and temperature. The plants were treated with 5×10^?6M of simazine, simeton, lenacil, isocil, diuron and fenuron in the nutrient solution. CO₂ uptake and transpiration of intact bean plants were measured continuously. The decrease in photosynthesis was more rapid at higher transpiration rates. For each herbicide the total transpiration to the 50% inhibition level of photosynthesis was almost constant at different rates of transpiration, indicating that the degree of inhibition is determined by the transpiration stream in the plants. Treatments with lenacil and diuron resulted in a lower degree of photosynthesis inhibition than did the other herbicides. The results are discussed in relation to uptake studies, herbicidal effects and adsorption phenomena of these and similar herbicides. They are also related to the field performance of such herbicides. Effet de la uitesse de la transpiration des haricots sur l'inhibition de la Photosynthèse par quelques herbicides administerés par les racines Résumé. L'inhibition de la Photosynthèse des haricots (Phaseolus vulgaris L.) par des herbicides administerés par les racines a été déterminèe à des taux différents de transpiration, obtenus en faisant varier l'humidité de I'air, l'intensité de la lumière et la température. Les plantes ont été traitées avec une concentration de 5 × 10^?6 M de simazine, de simétone, de lénacile, d'isocile, de diuron et de fenuron dans la solution nutritive. L'absorption du CO₂ et la transpiration des plantes intactes ont été mesurées en continu. La diminution de la Photosynthèse fut plus rapide pour un taux de transpiration élevé. Pour chaque herbicide, la transpiration totale jusqu'au niveau de 50% d'inhibition dc la Photosynthèse fut assez constante aux différents taux de transpiration, ce qui indique que le degré d'inhibition est déterminé par le courant de la transpiration dans les plantes. Le lénacile et le diuron ont moins influenceé la Photosynthèse que les autres herbicides. Les résultats ont été discutés par rapport à I'assimilation, aux effets phytotoxiques et aux phénomines de l'adsorption de ces herbicides et d'autres produits similaires, Les résultats ont été considerés aussi en relation avec l'effet de ces herbicides au champ. Einfluss der Transpìratìonsìntensität von Bohnen Pflanzen auf die Photosynthesekemmung nach Application einiger Herbizide über die Wurzel Zusammenfassung. Die Photosynthesekemmung von Bohnenpflanzen (Phaseolus vulgaris L.) durch einige üer die Wurzeln applizierte Herbizide wurde unter verschiedenen Transpirationsbedingungen, die durch Änderung der Luftfeuchtigkeit, Lichtintensität und Temperatur erhalten wurden, bestimmt. Die Pflanzen wurden mit 5 × 10^?6 M Simazin, Simeton, Lenacil, Isocil, Diuron und Fenuron in der Nährlösung behandelt. CO₂-Aufnahme und Transpiration intakter Pflanzen wurden kontinuierlich gemessen. Die Abnahme der Photosynthese war bei höherer Transpirationsintensität stärker. Für jedes Herbizid war die Gesamt transpiration bis zur Stufe der 50%-Hemmung bei verschiedenen Transpirationsintensitäten weitgehend konstant. Dieses Verhaiten zeigt, dass der Grad der Hemmung durch den Transpirationsstrom in der Pflanze bestimmt wird. Die Behandlung mit Lenacil und Diuron ergaben einen geringeren Hemmungsgrad als bei den übrigen Herbiziden. Die Ergebnisse werden im Hinblick auf Aufnahme, Herbizidwirkung und Adsorphánosphanomene dieser Herbizide besprochen. Sie werden auch auf die Wirkung dieser Herbizide im Freiland bezogen.     

Photosynthetic capacity of intact leaves of resistant and susceptible cultivars of Brassica napus L. to atrazine

The rate of photosynthesis in intact leaves attached to plants of an atrazine-resistant cultivar of Brassica napus L. was compared with that in leaves of an atrazine-susceptible, rather isogenic cultivar, in a number of irradiance series. The resistant cultivar had been obtained from the susceptible cultivar by crossing the resistant biotype of Brassica campestris L. with the susceptible cultivar of B. napus, and using the fourth back-cross for comparison. At a natural CO₂ concentration (360 cm³ m^?3) the rate of photosynthesis of leaves of the atrazine-resistant cultivar was significantly (17–21%) less than that of leaves of the susceptible cultivar, over the whole range of irradiances up to 250 W m^?2 At the enriched CO₂ concentration of 1500 cm^?3 m^?3 this reduction in rate amounted to 9–12%.     

Use of fluorescence induction to diagnose resistance of Alopecurus myosuroides Huds. (black-grass) to chlorotoluron

The inhibition of photosynthesis of detached black-grass leaves by chlorotoluron could be quantified by measuring the fluorescence induction using a sensor that almost fully suppressed the reflection component. The induction curve was measured twice on the same leaf spots, first after putting the leaves in the herbicide solution for 16 h, and again after placing the leaves in water for 1 day. Leaves from resistant plants showed partial to full recovery from the inhibition, while susceptible plants did not. These results for fluorescence induction were compared with the inhibition of photosynthesis rate in intact black-grass plants by chlorotoluron in the nutrient solution, and the recovery that occurred when the roots were placed again in herbicide-free nutrient solution. The similarity of the results indicates that the procedure for fluorescence induction can replace the more labour-intensive and complicated demonstration of inactivation by measuring photosynthesis rate. Each plant must be measured separately to avoid suppressing the differences between plants within a population. The method was used for samples from 22 fields in The Netherlands in which resistance of black-grass to chlorotoluron was suspected. The results indicate that substantial resistance was present in only two populations, but that weak resistance occurred in all fields. Utilisation de l'induction de fluorescence pour diagnostiquer la résistance au chlorotoluron chez le vulpin, Alopecurus myosuroides Huds. L'inhibition de la photosynthèse de feuilles de vulpin par le chorotoluron pourrait être quantifiee par la mesure de l'induction de fluorescence en utilisant un récepteur qui supprime quasiment la reflexion. La courbe d'induction était mesuree 2 fois, sur les memes fragments de feuille, la première après avoir mise pendant 16 h les feuilles dans la solution herbicide, et de nouveau après avoir placé les feuilles dans l'eau pendant un jour, Les feuilles des plantes resistantes se recuperaient partiellement à totalement de l'inhibition, tandis que les plantes sensibles ne le faisaient pas. Ces résultats sur l'induction de fluorescence ont été comparés avec le taux d'inhibition de la photosynthèse dans des plantes intactes de vulpin par le chlorotoluron dans la solution nutritive et avec la récupération qui apparaissait quand les racines étaient de nouveau placées dans une solution exempte d'herbicide, Les résultats similaires montrent que le procédé de I'induction de fluorescence peut remplacer la démonstration de l'inactivation, beaucoup plus laborieuse et compliquée par la mesure du taux de photosynthèse, Chaque plante doit être mesurée séparément pour éviter la suppression des différences entre piantes dans une population. La méthode a été utilisée pour les échantillons venant de 22 champs aux Pays-Bas dans lesquels on suspectait une résistance du vulpin au chlorotoluron. Les résultats montrent qu'une resistance réelle était seulement présente dans deux populations, mais qu'une faible résistance existait dans tous les champs. Fluorimetrische Diagnose der Resistenz von Alopecurus myosuroides Huds. (Acker-Fuchsschwanz) gegenüber Chlortoluron Die Hemmung der Photosynthese in isolierten Blättern von Acker-Fuchsschwanz durch Chlortoluron konnte durch Messung der Fluoreszenz-induktion bestimmt werden, wobei ein Sensor benutzt wurde, der die Reflektion fast vollständig ehminierte. Die Induktionskurve wurde zweimal gemessen, zum einen nach dem Einstetzen der Blätter für 16 h in die Herbizidlösung und zum andern nochmals nach einem Tag auf Wasser, Blätter resistenter Pflanzen erholten sich teilweise oder ganz von der Hemmung, solche empfindlicher Pflanzen nicht. Die Ergebnisse der Fluoreszenzinduktion wurden mit der Hemmung der Photosyntheserate intakter Pflanzen durch Chlortoluron in der Nährlösung und der Erholung nach Überführen der Wurzeln in herbizidfreie Nährlösung verglichen. Die Ähnlichkeit der Ergebnisse zeigt, daß man die arbeitsintensivere und komplizierte Bestimmung der Inaktivierung mittels Messung der Photosyntheserate durch die Fluoreszenzinduktion ersetzen kann. Jede Pflanze muß für sich gemessen werden, um ein Verwischen der Unterschiede zwischen den Pflanzen einer Population zu vermeiden. Die Methode wurde zur Untersuchung von Proben aus 22 Feldern in den Niederlanden angewandt, wo Resistenz von Acker-Fuchsschwanz gegenüber Chlortoluron vermutet wurde. Nur in 2 Populationen wurde eine volle Resistenz festgestellt, aber eine schwache Resistenz lag bei allen Fällen vor.     

Inhibition of photosynthesis in intact plants of biotypes resistant or susceptible to atrazine and cross-resistance to other herbicides

A concentration of atrazine of 0?1 mm 1^?1 in the nutrient solution resulted in complete inhibition of photosynthesis in intact leaves of susceptible biotypes of Amaranthus retroflexus L., Polygonum lapathifolium L., Chenopodium album L., Solanum nigrum L., Poa annua L. and Stellaria media (L.) Vill. within a few hours of treatment, whereas the inhibition of the resistant biotypes by the same concentration varied from small to moderate. In contrast, diuron (10 or 20 μm 1^?1) produced only minor differences between resistant and susceptible biotypes. The influence of some other herbicides on photosynthesis of these resistant biotypes was also smaller than that on the susceptible biotypes. This cross-resistance was evaluated with the resistance factor for intact leaves of Brassica napus L., A. retroflexus, and S. nigrum. This factor is equal to the ratio of the herbicide concentration in leaves of the resistant biotype to that in leaves of the susceptible biotype with inhibition to half-maximum rate of photosynthesis. This concentration in the leaves was calculated from the concentration in the nutrient solution, and the total transpiration divided by leaf area from the beginning of the herbicide treatment until the moment of half-maximum of photosynthesis. The resistance factors for intact leaves of A. retroflexus, S. nigrum and B. napus were 26–30 for atraton, 3–7 for metamitron, 2–9 for bromacil, 3–5 for monolinuron, 1 for diuron and < 1 for bentazone. For isolated chloroplasts much higher values have been reported. The reason for this discrepancy is not clear. A somewhat higher resistance factor (around 50–60) was derived after infiltration of detached leaves of these species with atraton solutions.     

Mortality of marine cultured rainbow trout, Oncorhynchus my kiss (Walbaum), during the summer in the Netherlands

Abstract. In northern Europe, rearing of rainbow trout, Oncorhynchus mykiss (Walbaum), in sea cages is a substantial part of fish culture. One of the major constraints for the development of this system in other parts of Europe is the unexplained mortality of fish during the summer. To investigate environmental aspects of this mortality, rainbow trout, cultured in cages in sea water, were monitored from May to October for three successive years. No evidence of bacterial involvement could be found, while water temperature and salinity strongly influence the mortality. This supports the suggestion that the mortality has been caused by patho-physiological changes due to higher metabolic requirements for osmoregulation at elevated water temperature in the saline environment which might result in a dissipation of O₂ by CO₂ on the hemoglobin.     

Recovery from inhibition of photosynthesis by metamitron in various plant species

Inhibition of photosynthesis by metamitron in the rooting medium and its subsequent recovery after transfer of the roots to herbicide-free nutrient solution was measured in eight plant species. Fast and complete recovery within a few hours after treatment showed that metamitron, once absorbed, was rapidly and completely inactivated in the leaves of sugar beet (Beta vulgaris L.). Inactivation in perennial ryegrass (Lolium perenne L.) was slower and incomplete. It was low in Echinochloa crusgalli (L.) P.B., Amaranthus retroflexus L., Alopecurus myosuroides Huds. and bean (Phaseolus vulgaris L.), and undetectable in maize (Zea mays L.) and Portulaca oleracea L. From the transpiration rate and the concentration of metamitron in the nutrient solution that just did not cause inhibition of photosynthesis in sugar beet, uptake and inactivation rates per unit leaf area were calculated to be at least 18·5 ng/cm²/h. The same external concentration markedly depressed photosynthesis in the other more susceptible species. After leaf sprays sugar beet plants gradually resumed the normal rate of photosynthesis, but bean plants did not recover.     

Photosynthetic inhibition in Phaseolus vulgaris

Similar injuries to the leaves of bean plants (Phaseolus vulgaris L. cv. Berna) were produced by exposure to CO₂-free air in the light and by ireatnient with simeton. The rate of production of leaf injuries and the degree of photosynthetic inhibition induced in plants exposed to CO₂-free air increased with exposure time and with light intensity. Exposure to CO₂-free nitrogen delayed the onset of the inhibition and the development of the injuries. These results showed some analogies with the action of herbicides which affect photosynthesis.