The Uptake of Growth Substances: XIV. PATTERNS OF UPTAKE BY LEMNA MINOR OF PHENOXYACETIC AND BENZOIC ACIDS FOLLOWING PROGRESSIVE CHLORINATION

The interrelationships between chemical structure and patternsof uptake by Lemna minor have been examined for (a) phenoxyaceticacid and its 2-, 4-, 2,4-, 2,6-, 3,5-, 2,5-, 2, 4, 5- and 2,4,6-chloroderivatives and (b) benzoic acid and its 2-, 2,4-, 2,5-, 2,3,6-chloro-and 3,6-dichloro-2-methoxy derivatives. All compounds contained¹⁴C in the carboxyl group. The plants from a clonal populationwere grown at a constant temperature and continuously illuminated. With progressive chlorination of phenoxyacetic acid, uptakeis enhanced, so that by 6 h there is a fourfold difference betweenthe monochloro- and trichloro-derivatives. In complete contrast,chlorination of benzoic acid greatly suppresses uptake and thedifferences associated with the degree of chlorination are smaller. Arising out of previous studies, the effects of adding streptomycin,synthalin, and cetyltri-methylammoniumbromide on the courseof uptake of individual members of the two series have beenexamined. Each of the additions can induce positive, negative,or null changes in the pattern of uptake, but the nature ofthe response is also dependent on the properties of the compound. These findings are discussed in relation to prior studies concerning(a) penetration into the leaves of Phaseolus vulgaris, (b) uptakeby excised segments of etiolated stems, and (c) changes in physico-chemicalproperties resulting from progressive chlorination. Many of the complexities still remain to be resolved but itseems clear that adsorption by Borne membrane system involvingthe carboxyl group of the entering acid and the positively chargedquaternary ammonium group of alpha-lecithin cannot be restrictedto compounds which are physiologically active as auxins or herbicides.