No abstract

The technique of microradioautography was used to study the absorption and translocation ofa,a,a-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine (trifluralin) by cotton (Gossypium hirsutumL., var. Coker 201) and soybean (Glycine max(L.) Merr., var. Lee). Radioactivity from14C-trifluralin was retained primarily on the surfaces of the roots of cotton and soybean. This was apparently due to a tenacious adsorption or binding of the radioactivity to the epidermis and cuticle. Entrance of radioactivity into the roots of these species was greatly facilitated by breaks in the epidermis, such as might occur from seedling diseases or mechanical damage. Within the roots, radioactivity was noted in the walls of the xylem vessels and cortical cells. Little movement out of the soybean roots was observed, but limited movement of radioactivity into the leaves of cotton, apparently via the metaxylem, was noted. Radioactivity accumulated in the protoxylem of the cotton stem where many elements appeared to be plugged. Results of this study indicate that care should be used in interpreting data from studies where loss of radioactivity from nutrient media is used as a criterion of herbicide absorption, and where gross radio autography is used as an indicator of herbicide translocation.

The techniques of cryostat sectioning, freeze-drying, and microradioautography were adapted to study the absorption and translocation of radio-labeled 3-(3,4-dichlorophenyl)-1,1-dimethylurea (14C-diuron) in root-treated cotton (Gossypium hirsutum L., var. Coker 201) plants. Diuron appeared to move primarily in the apoplast and to be transported acropetally and laterally in the transpiration stream. Radioactivity was observed to accumulate in striking concentrations in the lysigenous, or pigment, glands and the trichomes of the cotton plant. This accumulation is postulated to be a major factor in lowering the effective concentration of the herbicide in the leaves of cotton as compared to leaves of more susceptible plants, and thus may be a significant factor in the tolerance of cotton to diuron.

The technique of microautoradiography was used to study the localization of14C-SAN 6706 [4-chloro-5-(dimethylamino)-2-(α,α,α-trifluoro-m-tolyl)-3(2H-pyridazinone] in cotton (Gossypium hirsutumL. ‘Coker 203’), soybean [Glycine max(L.) Merr. ‘Lee’], and corn (Zea maysL. ‘W.F. 9’). SAN 6706 was removed from the treatment solutions by absorption and also by adsorption onto the surfaces of roots. Absorbed SAN 6706 appeared to move primarily in the apoplast and to be translocated acropetally and laterally in the transpiration stream. The herbicide accumulated in striking concentrations in the lysigenous glands and trichomes of the cotton plant. This accumulation is postulated to be a major factor in lowering the effective concentration of SAN 6706 in the leaves of cotton as compared to the leaves of the more susceptible soybean and corn plants, and thus may be a significant factor in the tolerance of cotton to SAN 6706.

Dichlormid, a safener for thiolcarbamate herbicides, was tank-mixed with several herbicidal inhibitors of photosystem II, or with the herbicide acifluorfen, and applied postemergence to Ipomoea hederacea plants. Dichlormid had no visible effects on the plants when applied alone, but interacted synergistically with the herbicides in the combination treatments. Dichlormid strongly decreased the ascorbic acid levels in the Ipomoea hederacea cotyledons. Ascorbate is known to protect plant tissue from photooxidative damage. The herbicides which interacted synergistically with dichlormid are believed to generate their phytotoxic action via the production of excess singlet oxygen. It is suggested that the decreased ascorbate levels in the Ipomoea hederacea cotyledons after dichlormid treatment result in an impaired singlet oxygen scavenging system and consequently lead to increased plant damage in the presence of singlet oxygen generating herbicides.