THE EFFECT OF SIMAZINE ON THE PHOTOFIXATION OF CO2 AND ON TRANSLOCATION OF ASSIMILATES IN NORWAY SPRUCE (PICEA ABIES)

Summary. A method of exposing seedlings of Norway spruce (Picea abies (L.) Karst.) to ¹⁴CO₂ is described. Within the 1st hr alter ¹⁴CO₂ exposure, no translocation of the ¹⁴C out of the treated branch could be observed. After a 24-hr period, however, the ¹⁴C in dormant seedlings had been translocated basipetally to part of the root system only, with no lateral diffusion of the ¹⁴C-compounds in the stem. About a week after exposure, both symplastic and apoplastic patterns of translocation had caused a more uniform distribution of ¹⁴C. In seedlings at active internode elongation, the translocation patterns were fundamentally identical to those in dormant seedlings, but the active shoot growth had led to a more uniform distribution of the ¹⁴C.
Simazine at 20 ppm had apparently stimulated both the photofixation of ¹⁴CO₂ and the rate of translocation of the ¹⁴C-assimilates. At 30 ppm, however, simazine had blocked the translocation of nutrients to the roots. On the other hand, the ¹⁴CO₂ uptake was not influenced. The simazine incubation had apparently no influence on the synthesis of cationic photosynthate.     

Uptake and metabolism of hexazinone in Rubus hispidus L. and Pyrus melanocarpa (Michx.) Willd

Rooted cuttings of Pyrus melanocarpa (Michx.) Willd. had a 3.5-fold greater tolerance to soil-applied hexazinone than those of Rubus hispidus L. in a greenhouse trial. R. hispidus accumulated four times more ¹⁴C-label in the foliage following root uptake of ¹⁴C-hexazinone than P. melano-carpa . Here, the greater uptake and susceptibility of R. hispidus was related to its greater root:fol-iage (weight) ratio compared to the tolerant P. melanocarpa . However, in whole plant metabolism studies employing younger plants there were no differences in ¹⁴C accumulation in the leaves. Here ¹⁴Chexazinone was converted to a number of hydroxylated and/or demethylated triazinone metabolites in both species following vacuum infiltration into leaf disks and root sections, or following root uptake in whole plants. A major difference in metabolism between the two species was the greater formation of the mono demethylated metabolite, B, [3-cyclohexyl-6-methylamino-l-methyl-l,3,5-triazine-2,4-dione] in P. melanocarpa which may also contribute to its greater tolerance. A loss of total ¹⁴Clabel from all plant parts with time may reflect cleavage of the ¹⁴C-ring-labelled herbicide.     

THE FATE OF PARAQUAT APPLIED TO PLANTS

Summary. Paraquat dichloride was applied to maize, tomato and broad bean plants as droplets of an aqueous solution and analysed al intervals. It was shown to be degraded under some conditions, but the amount of degradation was least under conditions which would have been most favourable for metabolism of the chemical. The analytical results and results from cation-exchange paper chromatography and thin layer chromatography showed that the degradation was caused by photochemical decomposition on the surface of the leaves of the plants, not by metabolism. The degradation was not observed in the dark, and only occurred to a significant extent in daylight in the summer.
Two photochemical degradation products from methyl-labelled paraquat-¹⁴C dichloride, viz., 4-carboxy-l-(methyl-¹⁴C)-pyridinium chloride and methylamine-¹⁴C hydrochloride, were isolated from plants sprayed with the herbicide.
Le devenir du paraquat dans les plantes traitées     

3,4,3',4'-RACHLOROAZOBENZENE: ITS TRANS-LOCATION AND METABOLISM IN RICE PLANTS

Summary. 3,4,3',4'-Tetrachloroazobenzene (TCAB) and TCAB-¹⁴C were supplied to the roots of rice ( Oryza sativa L.) plants in nutrient solution. An analysis of the shoots indicated that the TCAB was absorbed and translocated to the shoots. The translocated material was characterized by gas-liquid chromatography and mass spectrometry. Roots were exposed to saturation concentrations of TCAB-¹⁴C in liquid culture to determine the translocation and distribution of the compound. Only 5'6% of the total azobenzene present in the nutrient solution was absorbed by the intact rice plants and only 3'2% of the absorbed TCAB-¹⁴C was translocated to the shoots after 12 days of treatment. No TGAB was isolated from plants treated with propanil or 3,4-dichloroaniline after 14 days of treatment.     

TRANSLOCATION OF AMINOTRIAZOLE AND DALAPON IN AG ROPY RON REPENS (L.) BEAUV.

Summary. Tracer studies using single drops of solutions containing 3–amino-1,2,4–triazole-5–¹⁴C (aminotriazole-¹⁴C) or 2,2–dichloropropionic acid-2–¹⁴C (datapon-¹⁴C) revealed that in couch plants (Agropyron repens (L.) Beauv.) growing under field conditions in the autumn and at the stage where the aerial shoots were 40–50 cm long, both compounds moved in both symplast and apoplast. Dalapon was less mobile in the symplast than aminotriazole and only negligible amounts of dalapon were translocated to the rhizomes. The nodes of the treated shoots appeared to act as barriers to translocation, a phenomenon more pronounced for dalapon than for aminotriazole.
Application to a basal green leaf led to a more uniform distribution of the compounds within plants and rhizomes than when the application was made to the youngest fully-expanded leaf.
In couch plants with aerial shoots 10–15 cm long treated in the stubble, the distribution of both aminotriazole and dalapon was mainly restricted to the treated shoots. Even 15 days after application only trace amounts of radioactivity could be found in the rhizomes and untreated shoots.     

MOVEMENT AND FATE OF FLUORODIFEN-1'-14C IN CUCUMBER SEEDLINGS

Summary. Autoradiographs and liquid scintillation counts of cucumber ( Cucumis sativus L. cv. Ashley) seedlings indicated rapid absorption and translocation of radioactivity from fluorodifen-1'-¹⁴C ( p -nitrophenyl-α,α,α-trifluoro-2-nitro- p -tolyl ether labelled with ¹⁴C in the 1 position of the p -nitrophenyl ring). After 24 h in 1 mg/1 of fluoro-difen-1'-¹⁴C, 25% of the absorbed radioactivity was translocated from the roots.
Cucumber seedlings degraded fluorodifen-1'-¹⁴C via a pathway similar to that reported for peanut seedlings but at a slower rate. The major degradation products were p -nitrophenol and an unidentified polar compound (Unknown I). More rapid absorption and translocation coupled with slower degradation by cucumber as compared with peanut seedlings are factors which may contribute to the susceptibility of cucumber to fluorodifen.     

AN AUTORADIOGRAPHIC STUDY OF THE MOVEMENT OF 14C-LABELLED ASSIMILATES IN THE DEVELOPING WHEAT PLANT

Summary. ¹⁴CO₂ together with autoradiographic techniques was used to stuy the movement of labelled carbon within wheat plants at different stages in their development. Movement of ¹⁴C about the plain was found to be extensive in the early stages, gradually bccoming more localized until at a stage after ear emergence there was little transference of labelled carbon between tillers within a 24-hour period.
In the early stages of development ¹⁴C from leaves on the main shoot was transported throughout the plant but accumulated in greatest amounts in the meristematic regions. Assimilates produced by the leaves of newly formed tillers were distributed mainly to the meristematic regions of those tillers although labelled carbon was moved in into the rest of the plant. In the later stages of development of each tiller the labelled assimilate was restricted to the tiller itself and to any very young tillers associated with it. After car emergence the pattern of distribution of the labelled carbon from the youngest and second youngest leaves was found to differ. Movement was predominantly towards the ear from the flag leaf and towards the root system from the leaf below the flag.
It was noticed that mature leaves accumulated some labelled material and the possibility that this occurred via the transpiration stream following migration from phloem to xylem, as is the case with some of the case with some of the translocated herbicides, was investigated, but no indication of xylem transference was obtained.
The possible application of these studies to investigations into the relationship between the movement natural assimilates and of translocated herbicides is discussed.     

TRANSLOCATION OF 14C-ASSIMILATES AND 3-AMINO-1,2,4-TRIAZOLE AND ITS METABOLITES IN AGROPYRON REPENS

Summary. Translocation of 3-amino-1,2,4-triazole-5-¹⁴C (¹⁴C-aminotriazole) was compared to that of ¹⁴C-assimilates in couch grass ( Agropyron repens (L.) Beauv.) at three different growth stages.
Assimilates of ¹⁴CO₂ were translocated from the treated shoot to other shoots and rhizomes at the 2–3-leaf and 3–4-leaf stages of development. Much less labelled material was translocated into untreated shoots at the 5-leaf stage. More ¹⁴C-assimilates were translocated to the roots than to untreated shoots at all developmental stages. The translocation patterns of ¹⁴C-aminotriazole and ¹⁴C-assimilates were similar.
Two metabolites, A and B, were formed from ¹⁴C-aminotriazole, which chromatographed identically to previously described metabolites in Cirsium arvense (L.) Scop. A was further metabolized into B. Labelled aminotriazole and its two metabolites were translocated throughout the plants. Metabolite A was phytotoxic when concentrated and re-applied to couch grass, but its properties were not those of Unknown II from Cirsium arvense. They were the same as those of Unknown III. Whether or not metabolite A and Unknown III are identical was not established.
Migration des substances assimilables marquées au ¹⁴ C, du 3 amino-1,2,4-triazole et de ses métabolites chez Agropyron repens     

THE TRANSLOCATION AND DISTRIBUTION OF THREE LABELLED HERBICIDES IN PASPALUM DISTICHUM L.

Summary Plants of Paspalum distichum L. with two stolons growing over water were treated separately with the sodium salt of 2,2-dichloropropionic acid-³⁶C1 (dalapon), 3-amino-1,2,4-triazole-¹⁴C (amitrole) and 1,1'-dimethyl-4,4'-dipyridylium dichloride-¹⁴C (paraquat) at four different situations on one stolon. Autoradiographs showed that both the amitrole and dalapon label accumulated in the apices of the treated stolons and in some of the young shoots growing from the base of the plant. The ¹⁴C from the paraquat label showed predominantly xylem translocating with no apical accumulation and little basal translocation. The results indicate that young basal shoots rely to some extent on assimilates from the mature stolons but that there is little transport between mature stolons.
La migration et la distribution de trois Herbicides marqués dans Paspalum distichum L.     

Uptake and translocation of imazethapyr in peas as affected by parasitism of Orobanche crenata and herbicide application methods

[¹⁴C]-Imazethapyr was applied as a seed treatment and at plant pre-emergence and post-emergence to peas ( Pisum sativum L.) parasitized by Orobanche crenata Forsk. Herbicide uptake increased with time regardless of the application method. Uptake reached about 98%, 89%, 81% and 94% of the total herbicide applied for the seed coating, seed soaking, pre-emergence and post-emergence treatments respectively. Herbicide translocation within the host plants consistently differed between O. crenata -infected and non-infected plants. High levels of ¹⁴C activity were accumulated by parasitic plants from the host. In non-infected pea plants, pods were stronger sinks for imazethapyr than the other parts of the plant, regardless of the application method. The herbicide distribution in the pea plant: O. crenata complex showed the same pattern regardless of the application methods. However, accumulation of radioactivity in the parasite was lower with pre-emergence and post-emergence application than with the seed treatments. In addition, radioactivity concentration in O. crenata plants was slightly higher when [¹⁴C]-imazethapyr was applied to pea seeds by coating than by soaking.     

STUDIES ON THE TRANSLOCATION IN AGROPYRON REPENS OF 14C-LABELLED 2,2-DICHLOROPROPIONIC ACID

Summary. Previous findings suggested that the translocation in Agropyron repens of 2,2-dichloropropionic acid (dalapon) may be considerably affected by the transpiration rate. This relationship has been studied further in the present investigation using ¹⁴C-labelled material and autoradiography.
It was found that when dalapon was applied to the leaves and the treated plants were placed in darkness a reduction in the transpiration rate of ca. 90% was associated with a marked increase in the amount of dalapon translocation into the roots and tillers. The evidence provided by the autoradiographs was confirmed by a quantitative assay of the ¹⁴C present in the roots. It was also found, however, that translocation was not appreciably affected either by a 50% reduction in the light intensity or when the transpiration rate was reduced by placing the plaints under conditions of high humidity in the light or by the application of white petroleum jelly to the leaves. An alternative hypothesis, namely that the effect of darkness on the movement of the herbicide might be due to changes induced in the normal pattern of assimilate translocation was also investigated but was not supported by the results obtained. Further experimentss, in which various parts of the treated shoot were placed in the dark, suggested that the effect of darkness on the translocation of dalapon is exerted primarily on the treated leaf itself.
Etudes sur to migration dans Agropyron repens de l'acide 2,2-dichloropropionique marqué avec ¹⁴C     

Phytotoxic activity of root absorbed glyphosate in corn seedlings (Zea mays L.)

Growth chamber experiments were conducted in order to study the absorption, translocation and activity of glyphosate when applied to roots with aqueous solution avoiding any glyphosate–substrate interaction. Corn seedlings at the first leaf stage were set up in individual graduated cylinders containing different solutions of ¹⁴C-glyphosate (0–30 mg ae kg⁻¹). After 26 h of root exposure, plants were transferred to fresh nutrient solution and grown for the next 5 days. After harvest, plants were separated into seed, root, mesocotyle, coleoptile, cotyledon, first leaf and all new leaves (apex), and quantified ¹⁴C radioactivity contained in each part. Glyphosate uptake was only 11% of the theoretical mass flow into the plant. The amount of glyphosate translocated from roots was positively correlated with plant uptake ( P  < 0.01). Total plant fresh weight presented a logistic response to glyphosate amounts, including a growth stimulant effect (hormesis), when plants absorbed less than 0.6 µg. The treated plants presented a normal pattern of glyphosate allocation, with the apex the principal sink, accumulating more than 38% of mobilized glyphosate. When corn plants absorbed more than 0.6 µg they showed a decrease in growth. The relatively high glyphosate quantities allocated in the new leaves showed the relevance of the symplastic pathway in the translocation process for root absorbed glyphosate.     

EFFECT OF 2,4-D AND PICLORAM ON TRANSLOCATION OF 14C-ASSIMILATES IN VITIS VINIEERA L.

Summary. High concentrations of 2,4-D and picloram interfered with the downward movement of ¹⁴c-assimilates infield-grown vines. The interference in translocation was appreciably greater with picloram than it was with 2,4-D, Although basipetal translocation was retarded, translocation within the treated shoots continued from the vegetative part to the clusters. Translocation of 2,4-D appeared to follow the same route as ¹⁴c-assimilatcs for the most part. Formative effects were absent on untreated grape shoots although the adjacent shoots treated with 2,4-D or picloram on the same cordons were killed; however, formative effects were evident on some of the stump sprouts which developed after the vines were harvested. The malformed leaves on the stump sprouts were twelve or more nodes from the base of the shoots, while ¹⁴c was in the more basal leaves.
Thompson Seedless (Sultanina) rootings treated with 20 000 ppm 2,4-D or picloram transported less ¹⁴C to the roots than did the controls. Treatment with either herbicide resulted in a marked increase in the labelling of the stems.
Effet du 2,4-D et du pichlorame sur la migration de métabolites marqués au ¹⁴C dans Vitis vinifera L.     

DEGRADATION OF FLUORODIFEN-1'-14C BY PEANUT SEEDLING ROOTS

Summary. Degradation of p -nitrophenyl-α,α,α:-trifluoro-2-nitro- p -tolyl ether (fluorodifen) labelled with ¹⁴C in the 1 position of the p -nitrophenyl ring (1'-¹⁴C) proceeded rapidly in peanut ( Arachis hypogaea L. cv. Starr) seedling roots. All degradation products were present after only 2 h.
The major degradation products for fluorodifen-1'-¹⁴C were the water-soluble compounds p -nitrophenol and Unknown I, a polar compound or complex which remained on the origin during thin-layer chromatography. Minor products included p -nitrophenyl-α,α,α-trifluoro-2-amino- p -tolyl ether, p -aminophenyl-α,α,α-trifluoro-2-nitro- p -tolyl ether and traces of p -aminophenol. No p -aminophenyl-α,α,α-trinuoro-2-amino- p -tolyl ether was detected. The p -aminophenol previously reported [ PL Physiol., Lancaster , 44,1397-1401 (1969)] was not p -aminophenol, but primarily Unknown I with a possible trace of p -aminophenol.
Fluorodifen continued to be absorbed throughout the 72-h treatment period.     

A RAPID BIOASSAY FOR SIMULTANEOUS IDENTIFICATION AND QUANTITATJON OF PICLORAM IN AQUEOUS SOLUTION

Summary. When seeds of lettuce ( Lactuca sativa L.) were placed on small squares of filter paper moistened with solutions of picloram (4-amino-3,5,6-trichloropicolinic acid), the degree of inhibition on of root and hypocotyl elongation 72 hr later was related to picloram concentration. Inhibition was a useful parameter in determining quantities of picloram ranging from 0·03 to 7·2 μg. (Growth stimulation occurred from 0·00072 to 0·0072 μg. After paper chromatography of plant exudates containing ¹⁴C-labelled picloram, location and quantities of picloram on the chromatograms were determined by the lettuce bioassay and compared with determinations by the methods of ultraviolet light sensitivity, ¹⁴C 4π strip scanning and 14 C dilution calculations. R_f values determined lay all methods were identical, and the quantitative determination by the bioassay agreed closely with the calculations based on the amount of ¹⁴C detected by liquid scintillation counting.
Un essai biologique rapide d'idntification et de dosage de piclorame en solution aqueuse     

Biotransformation of [ring-U-14C]atrazine to dealkylated and hydroxylated metabolites in cell-suspension cultures

The biconversion of [¹⁴C]atrazine to deaikyt-ated and hydroxylated products was studied in heteroirophic cell-suspension cultures of carrot ( Daucus caroia L.), Agrostemma githago L. (corn cockle). Digitalis purpurea L. (purple foxglove), soyabean ( Giycine max L. Merr; four different cultivars). Datura stramonium L. (thorn-apple) and wheat ( Tritician aestivum L.). During 48 h of incubation, the herbicide was biotransformed by all species; turnovers yields differed considerably and were between 10.1% and 88.0% of applied ¹⁴C. Differences were also observed among the soyabean cultivars (10.1-73.5%). Hydroxy-atrazine, de-ethyl-, deisopropyl- and de-ethyt-deisopropylatrazine formed in the cultures were identified by thin-layer chromatography (tlc) (co-chromatography with reference compounds); deaikyiated metabolites were also proved by gas chromatography–mass spectrometry (gc–ms). In addition, highly polar transformation products emerged that were not identified. Portions of non-extractable residues were below 5% (one soyabean cultivar: 8.9%). Atrazine was metabolized by the cells, mainly to its dealkylated derivatives and hydroxyatrazine (totals of 9.4-54, 5%), whereas portions of highly polar products were lower (0.1-26.1%). Exceptions were A. githago (26.0 and 33.6%, respectively) and D, purpurea (4.5 and 25.2% respectively). Thus, plants generally contribute to the environmental degradation of atrazine.     

Distribution of 14C-glyphosate in legumes parasitised by Orobanche crenata

Absorption and translocation of ¹⁴C-glyphosate was evaluated under controlled conditions in peas ( Pisum sativum L.) and broad beans ( Vicia faba L.) parasitised or not by crenate broomrape Orobanche crenata Forsk.). Absorption increased with time up to 12 days after treatment, and reached about 50% of the ¹⁴C-glyphosate applied. Three days after treatment 70–85% of the total herbicide absorbed had been translocated out of the treated leaflet. There was no consistent differ ence in absorption and translocation between infected and non-infected plants 12 days after treatment. The ¹⁴C-glyphosate concentration in the root system increased with time in broad beans. In peas it remained more or less constant from 3 days after treatment. Generally, pods were stronger sinks for glyphosate than other parts of the plant. Herbicide accumulation in broomrape increased with its growth stage, and the parasite was a much stronger sink for glyphosate than the legume root system.     

Root exudation of diclofop-methyl and triasulfuron from foliar-treated durum wheat and ryegrass

In this study, we evaluated the release of diclofop-methyl and triasulfuron from the roots of foliar-treated ryegrass and wheat. The study with ¹⁴C-diclofop-methyl indicated a basipetal translocation of foliar-applied herbicide in wheat and ryegrass. No root exudation from ¹⁴C-diclofop-methyl-treated wheat plants was observed, while 20 days after treatment (DAT) 0.2–0.9% of radioactivity absorbed by ryegrass was found exuded in the growing medium. Root exudation was stimulated three to six times by the presence of untreated wheat or ryegrass sharing the growing medium with diclofop-methyl-treated ryegrass. No subsequent uptake of exuded radiolabel by untreated plants (ryegrass or wheat) in the same pot with ¹⁴C-diclofop-methyl-treated ryegrass was observed. The study with ¹⁴C-triasulfuron indicated a basipetal translocation of foliar-applied herbicide in wheat and ryegrass and also into the growing medium. By 20 DAT, 0.5–4.2% of radioactivity absorbed by wheat or ryegrass was found exuded in the growing medium. The presence of untreated plants (wheat or ryegrass) in the same pot as triasulfuron-treated ryegrass or wheat induced exudation seven to 32 times more. The study also revealed a subsequent uptake of exuded compounds by untreated wheat or ryegrass sharing the medium of ¹⁴C-triasulfuron-treated plants. This study has demonstrated for the first time that the root exudation of exogenous compounds can be related to plant arrangement in pots. The implication is that herbicide root exudation and transfer, a form of allelopathy, could be significant in the field. A precise estimation of environmental fate, unexpected ecological side effects and residual activity of herbicides may require quantification of such exudation.     

AN AUTORADIOGRAPHIC STUDY OF THE DISTRIBUTION OF 14C LABELLED ASSIMILATES AT DIFFERENT STAGES OF DEVELOPMENT OF OXALIS LATIFOLIA H.B.K. AND O. PES-CAPRAE L.

Summary. An autoradiographic study of the distribution of ¹⁴C-labelled assimilates, derived from ¹⁴CO₂ fed to the aerial parts, was made at ten different developmental stages of Oxalis latifolia H.B.K. and Oxalis pes-caprae L. Changing patterns of distribution of labelled assimilates to the underground parts of both species were revealed. These patterns are discussed in the context of the timing of control by defoliation and by foliageapplied herbicides.
Etude autoradiographique de la distribution des métabolites marqués an ¹⁴C à différents stades de développement de l'Oxalis latifolia H.B.K. et de l' O. pes-caprae L.     

A qualitative quick-test for detection of herbicide resistance to tribenuron-methyl in Papaver rhoeas

A qualitative seed-based method useful for the detection of resistance to the herbicide tribenuron-methyl in Papaver rhoeas L. is described. Seeds were germinated on 35 mL of a 1.3% agar medium containing 2 g KNO₃ L^–1 in 8.5 cm Petri dishes in a growth chamber under 20 μmol s^–1 m^–2 of fluorescent light. When 0.24 μM tribenuron-methyl or more was added, growth in susceptible plants stopped after the cotyledon stage and they turned chlorotic. The resistant plants continued developing new leaves. The same effect was achieved when 0.2 g gibberellin (GA₃) L^–1 and 7.68 μM tribenuron-methyl or 0.5 g GA₃ L^–1 and 61.44 μM tribenuron-methyl were added. Germination percentage rose with gibberellin in the presence or absence of the herbicide. Plants developed rapidly, with only about 14 d needed to finish the test but sometimes root growth was reduced because of the addition of gibberellin. In the absence of gibberellin but in the presence of the herbicide, plants grew more slowly and developed smaller leaves with a 17-d evaluation period requirement. The test was validated with pot experiments in a greenhouse and also with field trials. The best combination was found to be 0.2 g GA₃ L^–1 and 7.68 μM tribenuron-methyl, assuring homogenous germination and testing of dormant seeds but avoiding root inhibition associated with too much gibberellin.