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.     

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     

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.     

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 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.     

TRANSLOCATION STUDIES WITH ENDOTHAL-14C IN POTAMOGETON NODOSUS POIR.

Summary. Plants of Potamogeton nodosus, a submersed aquatic, were treated with the di-sodium salt of 7-oxabicyclo(2,2,l)heptane-2,3-dicarboxylic acid-¹⁴C (endothal-¹⁴C). Gross radioautographs showed that the ¹⁴C label moved from mature photosynthesizing leaves and accumulated in the apices and developing secondary plants. Similar results were obtained with mid-leaf, stem (internode) and winter-bud applications. No move-ment of radioactivity occurred following root treatment. The results indicate symplastic translocation of endothal-¹⁴C when applied to the leaf, stem or winter bud. It is suggested that endothal can cause the death of plants by direct injury to root tissues subsequent to absorption.
Recherches sur la migration de l'endothal-¹⁴C dans le Potamogeton nodosus Poir.     

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 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     

ABSORPTION AND TRANSLOCATION OF HERBICIDES BY THOMPSON SEEDLESS (SULTANINA) CRAPE, VITIS VINIFERA L.

Summary. Absorption and translocation of ¹⁴C-labelled herbicides applied in culture solutions lo the roots and in concentrated drops to mature leaves of 'Thompson Seedless' (Sultanina) cuttings were studied. Neither 2,4-D nor paraquat, and only traces of 2,4,5-T translocated from the roots to the shoot. Dicamba, amitrole, diuron, monuron, simazine and atrazine readily moved from the roots to the shoots. The substituted ureas and s -triazines were mobile only in the xylem or cell walls (apoplast), while dicamba and amitrole were mobile in the apoplast and symplast (living protoplasm). Both 2,4-D and 2,4,5-T moved almost entirely in the symplast. Paraquat moved only slightly in either apoplast or symplast. Stability of the herbicides in the plants varied, as judged by the detection of label in ethanol-insoluble products. Dicamba was considerably more stable than 2,4,5-T which, in turn, was more stable than 2,4-D. Diuron was more stable than either atrazine or simazine. Amitrole largely was converted into ethanol-insoluble products in 30 days. Paraquat was not extractable with ethanol.
Absorption et migration d'herbicides chez une vigne: Thompson Seedless (Sultanina), Vitis vinifera L.     

THE SELECTIVE ACTION OF PICLORAM IN RED MAPLE AND WHITE ASH

Summary. White ash ( Fraxinus americana L. ) trees, 2 years of age, treated continuously with 10 ppm picloram (4-amino-3,5,6-trichloropicolinic acid) in nutrient culture were only slightly injured after 4 weeks whereas red maple ( Acer rubrum L.) trees were killed after only 2 weeks treatment.
When the roots were exposed to 10 ppm ¹⁴C-picloram, the rate of root uptake, acropetal translocation in the stem, and accumulation in the leaves was much lower in the susceptible red maple than in the tolerant white ash. The foliar penetration and translocation of ¹⁴C-picloram applied to the leaves was very slight but similar in both species. Although a radiolabelled picloram metabolite was isolated from plant extracts, it was formed at equal rates in both species.
It was concluded that the tolerance of white ash was not related to lower rates of picloram uptake or faster rates of picloram detoxication. It was postulated that the high susceptibility of red maple was due to a blockage of the xylem by picloram which caused death by a dessication of the leaves and upper stems.
Action sélective du piclorame sur Fraxinus amerieana L. et Acer rubrum L.     

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.     

PRELIMINARY STUDIES ON THE TRANSLOCATION OF 14C-LABELLED HERBICIDES IN BRACKEN (PTERIDIUM AQUILINUM)

Summary. The translocation of ¹⁴C-labelled herbieides in field bracken has been sludied in some preliminary experiments by means of autoradiography. A detailed account is given of the methods employed. It is shown that when 2,4-D is applied to fronds at different stages of development movement of the tracer into the rhizome is considerably greater from parts of the frond which are still immature. Trasnslocation within the frond is predominantly basipetal at all stages of development; within the rhizome the direction of movement appears to be determined primarily by the nature of the vascular connections with the treated pinna.
In a comparison between the translocation of 2,4-D, 4-CPA and dalapon no difference was apparent after 24 hours, but when the treatment period was extended to 96 hours there was evidence that 4-CPA bad been translocated in a considerably greater amount than either of the other two herbicides.
Rechrches iréliminaires sur la migration des herbieides marqués am ¹⁴ C dans la fougrère algle (Pteridium aquilinum)     

A PRELIMINARY INVESTIGATION OF THE PENETRATION AND TRANSLOCATION OF 2,4,5-T IN SOME TROPICAL TREES

Summary The relative mobility of ¹⁴C-labelled 2,4,5-T in the trunks of four different tree species was tested in dry and wet seasons, with the intention of observing the difference in translocation pattern between the susceptible ( Piptadeniastrum africanum, Celtis mildbraedii ) and the tolerant ( Xylopia quintasii, Ricinodendron heudelotii ) species, Nine trees were analysed altogether. There was a consistent pattern of adsorption and retention of the arboricide by the phloem of the four sensitive trees and downward movement of the material was marked, but in the five resistant trees the chemical was distributed upward to a greater extent in the transpiration stream. Thus in the susceptible species where there is more phloem movement the chcmical is least mobile, whereas in the tolerant ones where the chemical moves in the xylem, it is most mobile. Both types of investigation (longitudinal and radial) indicate that the killing action in the sensitive species is due to the retention of the chemical by the phloem, and that its failure to kill the tolerant trees is due to the upward movement in the transpiration stream via the xylem.     

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.     

Visual and PCR assessment of light leaf spot (Pyrenopeziza brassicae) on winter oilseed rape (Brassica napus) cultivars

Methods to assess light leaf spot ( Pyrenopeziza brassicae ) on winter oilseed rape cultivars were compared in laboratory, controlled-environment and field experiments. In controlled-environment experiments with seedling leaves inoculated at GS 1,4, the greatest differences in percentage area affected by P. brassicae sporulation were observed with inoculum concentrations of 4 × 10³ or 4 × 10⁴ spores mL⁻¹, rather than 4 × 10² or 4 × 10⁵ spores mL⁻¹, but older leaves had begun to senesce before assessment, particularly where they were severely affected by P. brassicae . In winter oilseed rape field experiments, a severe light leaf spot epidemic developed in 2002/03 (inoculated, September/October rainfall 127·2 mm) but not in 2003/04 (uninoculated, September/October rainfall 40·7 mm). In-plot assessments discriminated between cultivars best in February/March in 2003 and June in 2004, but sometimes failed to detect plots with many infected plants (e.g. March/April 2004). Ranking of cultivar resistance differed between seedling experiments done under controlled-environment conditions and field experiments. The sensitivity of detection of P. brassicae DNA extracted from culture was greater using the PCR primer pair PbITSF/PbITSR than using primers Pb1/Pb2. P. brassicae was detected by PCR (PbITS primers) in leaves from controlled-environment experiments immediately and up to 14 days after inoculation, and in leaves sampled from field experiments 2 months before detection by visual assessment.     

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.     

Effectiveness of systemic resistance in bean against foliar and soilborne pathogens as induced by biological and chemical means

Unifoliate leaves of 9-day-old green bean, Phaseolus vulgaris cv. Redlands Pioneer, were inoculated with 10⁴ conidia/ml Colletotrichum lindemuthianum , causing local lesions, or sprayed with 20 μg 2, 6-dichloro-isonicotinic acid/ml formulated by Ciba-Geigy Ltd as CGA 41396. At various times afterwards (7–16 days), first, second or third trifoliate leaves of these plants were challenge-inoculated with 10⁵ conidia/ml C. lindemuthianum or with the rust pathogen, Uromyces appendiculatus. The numbers of anthracnose lesions or rust uredinia resulting from challenge-inoculation were reduced to similar extents by both pre-treatments compared with control plants. Halo blight, caused by Pseudomonas syringae pv. phaseolicola , was reduced in first trifoliates following treatment of unifoliate leaves 6 days earlier with CGA 41396. Induced resistance to root-infecting pathogens was not observed when stems of either 14- or 16-day-old plants were inoculated with mycelial plugs of Fusarium solani f. sp. phaseoli , or when 11- and 15-day-old plants were inoculated with Rhizoctonia sp., Treatment with CGA 41396 did not protect seedlings when they were transplanted into a mix containing the Fusarium sp. 1 day later.     

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.     

Observations on the physiological basis for the selectivity of morfamquat to graminaceous plants

The bipyridylium herbicide morfamquat damages dicotyledon plants in a similar way to paraquat but unlike paraquat, has little activity on Gramineae such as cocksfoot, wheat and maize. Results are presented which show that this selective action is not due to differences in the amounts of chemical taken up by treated leaves of susceptible and resistant plants or to differences in the degree of movement in plants. Freeze-thaw experiments show that the plasmalemma and tonoplast membranes of sensitive and resistant weeds are less permeable to morfamquat than to paraquat. Whilst this could account for differences in activity of the two herbicides on cocksfoot, further evidence is given which shows that selectivity is not due to differences in morfamquat movement from free space to cytoplasm. Differential movement from cytoplasm into the chloroplasts of resistant and susceptible species may be the basis of the selective action, but several other mechanisms of selectivity are also mentioned.     

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.