Chloroplasts isolated from spinach (Spinacia oleracea L.) leaves were used to study mechanisms of toxicity from 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron). Light was needed to initiate diuron injury. The addition of ascorbate plus 2,6-dichlorophenylindolephenol (DPIP) as an electron donor system completely protected the chloroplasts from diuron-induced toxicity. The protective effect from the electron donor system occurred only in functional chloroplasts. Diuron caused rapid and extensive chlorophyll degradation at chlorophyll: diuron ratios of 200:1 and lower. At higher ratios the effect was much less measurable. The electron donor system gave complete protection in the presence of methylamine HCl, a known inhibitor of photophosphorylation, indicating that a deficiency of ATP was not the primary cause of diuron toxicity. Time-course studies showed that carotenoid pigments began to degrade before initiation of chlorophyll degradation. These results are interpreted as supporting a hypothesis that diuron induces phytotoxicity by catalyzing lethal photosensitized oxidations in the cell. This may occur as a result of (a) a greater concentration of oxidized chlorophyll caused by an interruption of electron flow and (b) an inhibition of NADPH formation which is necessary to maintain a functional carotenoid protective mechanism.

Two wild oat (Avena fatua L.) biotypes and two barley (Hordeum vulgare L.) varieties known to have intraspecific differential response to foliarly-applied 4-chloro-2-butynyl m-chlorocarbanilate (barban) were studied. When barban was applied to the roots, the intraspecific differential response (measured by shoot retardation) was maintained in both species but to a much lesser extent than previously observed with foliar application. Wild oat maintained a greater differential response than barley. Therefore, the factors causing the differential response to foliarly-applied barban may reside primarily in the leaves of both species but to some extent elsewhere (perhaps at the plant apex) in the wild oat biotypes and to a lesser extent elsewhere in the barley varieties. Differential response to foliar applications was not caused by differential uptake, but may be caused primarily by the susceptible biotype or variety's reduced ability to degrade barban beyond 3-chloroaniline. This might cause the greater build-up of compound X (a water-soluble 3-chloroaniline-containing metabolite of barban) observed in the susceptible biotype or variety. Compound X appeared to be nonphytotoxic. The build-up of compound X in turn may reduce the rate of metabolism of barban resulting in the greater amount of free barban found in the treated leaf of the susceptible biotype or variety 12 to 24 hr after treatment. This greater amount of free barban in the leaf of the susceptible biotype or variety may be responsible for the differential response to foliar applications of barban. Evidence for this partial explanation of the differential response was better for barley than for wild oat.

The movement and persistence of 4-amino-3,5,6-trichloropicolinic acid (picloram) in an Osborne clay soil was determined over a 4-year period. Picloram concentrations were determined with soybean (Glycine max (L.) Merr. ‘Altona’) as the bioassay plant. Application rates ranged from 35 to 700 g/ha. Movement and dissipation of picloram were neglible under low soil moisture conditions, but under high rainfall conditions picloram was leached into the 30 to 60-cm depth. A greater percent of the picloram was leached at the higher application rates. Dissipation increased with temperature (days over 27 C) and decreased with increasing depth in the soil profile. Two applications of picloram at 70 g/ha applied in 2 successive years showed no detectable accumulation, but accumulation occurred from two applications of 350 g/ha; 32% of the activity remained after approximately 2 years.

Foliar-applied 3-[p-(p-chlorophenoxy)phenyl]-1,1-dimethylurea (chloroxuron), chloroxuron with dodecyl ether polyethylene glycol surfactant, and dimethylamine salt of 4-(2,4-dichlorophenoxy)butyric acid (2,4-DB) effectively controlled cocklbur (Xanthium sp.) in soybeans (Glycine max (L.) Merr. ‘Hampton’ or ‘Lee’). While treatments caused crop injury, treated soybeans produced higher seed yields than untreated soybeans infested with cocklebur plants. Seed yields from soybeans growing free of cocklebur were not reduced by treatment with chloroxuron or chloroxuron with surfactant but in some cases were reduced by 2,4-DB treatment.

Trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) at 10−5 M applied to etiolated corn (Zea mays L. ‘Michigan 500′) seedlings 6 or 12 hr before the isolation of chromatin from the roots markedly reduced ribonucleic acid (RNA) synthesis supported by the chromatin. The addition of Escherichia coli RNA polymerase failed to overcome the inhibition. Trifluralin increased the melting temperature of the chromatin. The presence of trifluralin during the isolation and reaction procedure inhibited RNA synthesis indicating possible trifluralin binding to the chromatin with subsequent reduction of template availability for transcription. Trifluralin did not inhibit chromatin activity in soybean [Glycine max (L.) Merr. ‘Hark’] seedlings.

Primary leaves of 17-day-old-bean (Phaseolus vulgaris L. ‘Black Valentine’) were treated with 14C-labeled dimethylsulfoxide (DMSO), 3,6-dichloro-o-anisic acid (dicamba), 1,1′-dimethyl-4,4′-dipyridinium salt (paraquat), and 2-chloro-4-(ethylamino)-6-(isopropylamino-s-triazine (atrazine). Each herbicide was tested alone, and in combination with 30% DMSO, 0.25% Tween 80 (nonionic surfactant containing polyoxyethylene sorbitan monooleate), or both. DMSO at concentrations of 25% or more caused varying degrees of acute toxicity. However, a small amount of radioactive carbon generally was distributed throughout the plant 5 days after application of DMSO-14C, as determined by autoradiography and counting. Tween 80 enhanced whereas DMSO had little effect on the absorption and translocation of dicamba, a phloem-mobile herbicide. The contact toxicity and apoplastic movement of paraquat was increased with DMSO. Tween 80 enhanced eight-fold and DMSO, two-fold, the foliar uptake and (apoplastic) movement of atrazine within the treated leaves.

Bacterial production of CO2 from sucrose substrate increased growth of seven species of algae in CO2-limited laboratory cultures. Decomposition of organic matter in pond water also supplied enough CO2 to support good algal growth in cultures deprived of other sources of CO2. Estimates of CO2 production from decay of dissolved organic matter in six pond waters ranged from 0.32 to 3.53 mg/L per 24 hr. The carbonate-bicarbonate equilibrium system is a major source of CO2 for algal photosynthesis. However, in waters of low or extremely high alkalinity, this system will not support high rates of photosynthesis. In such waters CO2 from decomposition will stimulate photosynthesis. Decomposable organic compounds must be considered with nitrogen and phosphorus as factors responsible for accelerated eutrophication and nuisance algal blooms.

Corn (Zea mays L. ‘Dixie 18′) leaf discs were incubated in light or darkness in dilute solutions of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) with and without 6-furfurylamino-purine (kinetin). Kinetin decreased chlorophyll loss in light whereas atrazine had no effect. In darkness atrazine at a concentration of 5 × 10−8M increased clorophyll a retention in the absence of exogenous kinetin; but in the presence of 1.5 μg/ml of kinetin, the herbicide increased loss of chlorophyll a. Increasing the kinetin concentration to 15 μg/ml relieved the effect of 5 × 10−8M atrazine, but 10−7M atrazine increased chlorophyll loss. Higher concentrations of kinetin (150 and 1500 μg/ml) prevented all effects of atrazine. Factorial analysis revealed a highly significant interaction between atrazine and kinetin.

Applications of 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) at 10−4, 10−5, and 10−6 M to 4-day-old etiolated soybean [Glycine max (L.) Merr. ‘Mark’] seedlings 6 hr before the isolation of chromatin enhanced the chromatin directed ribonucleic acid (RNA) synthesis by 16, 65, and 40%, respectively. The magnitude of this inductive effect increased with an increasing interval of time from 6 to 24 hr between application and chromatin isolation. The basis for the effect appeared to be an atrazine-mediated increase in chromatin template availability. The presence of atrazine during extraction and the assay was sufficient to evoke the response. This effect on chromatin activity was not observed for 2-hydroxy-4-(ethylamino)-6-isopropylamino)-s-triazine (hydroxyatrazine) or for atrazine on corn (Zea mays L. ‘Michigan 400′).