Competition between the Plant-parasitic Nematodes Pratylenchus neglectus and Meloidogyne chitwoodi.

In experiments on competition between Pratylenchus neglectus and Meloidogyne chitwoodi in barley, the species that parasitized the roots first inhibited penetration by the latter species. Prior presence of P. neglectus impeded the development of M. chitwoodi. Pratylenchus neglectus reduced egg production, final population levels, and reproductive index of M. chitwoodi. The reduction was linearly related to initial population densities of P. neglectus. Initial population densities of M. chitwoodi had no effect on final population levels of P. neglectus. Carbon assimilation by barley plants was reduced when either nematode species was present alone, but not when both were present together. Both nematode species assimilated lower amounts of carbon when present together than when present alone. A split-root experiment demonstrated that translocatable chemicals were not involved in the competition between the two species.

Binding of the herbicide trifluralin to Chlamydomonas flagellar tubulin.

Colchicine-binding tubulin was isolated from the centre 2 axoneme microtubules from the flagella of the alga Chlamydomonas eugametos. Incubating this tubulin with 5-8 micron [14C]trifluralin resulted in significant and reproducible binding of trifluralin to tubulin. The specificity of binding was determined by demonstrating that limited or no binding occurred to flagellar membrane and matrix protein, higher plant proteins, or bovine serum albumin. It was concluded that trifluralin, at obtainable soluble concentrations, specifically inhibits microtubule-mediated processes in plants. To date no effect of trifluralin on animal microtubule systems has been reported; therefore, it is suggested that trifluralin has revealed a pharmacological difference between plant and animal tubulin.

Absorption of 2,4-Dichlorophenoxyacetic Acid and 3-(p-Chlorophenyl)-1, 1-dimethylurea (Monuron) by Barley Roots.

Absorption from culture solution of the herbicides 2, 4-dichlorophenoxyacetic acid (2, 4-D) and 3-(p-chlorophenyl)-1, 1-dimethylurea (Monuron) by excised barley (Hordeum vulgare L.) roots was studied to determine whether absorption was due to an active or a passive mechanism. Herbicide absorption was followed at low temperature, under anaerobic conditions, and in the presence of metabolic inhibitors and compounds of structure similar to that of the herbicide. Total absorption was divided into two phases, exchangeable and nonexchangeable herbicide, by washing the roots for 1 hour following absorption. Absorption of both exchangeable and non-exchangeable 2, 4-D appeared to depend on a supply of metabolic energy which suggests that an active mechanism may be involved. A possible conclusion is that 2, 4-D is absorbed by roots by an adsorption mechanism and that energy is required to maintain the integrity of the absorbing surfaces of the cell. In contrast, absorption of Monuron was independent of an energy supply. It is concluded that the bulk of the Monuron absorbed was taken up passively by diffusion.