INTERRELATIONSHIPS BETWEEN THE 



UPTAKE OF 2:4-DICHLOROPHENOXYAGETIG 



ACID, GROWTH, AND ION ABSORPTION 



G. E. Blackman 



Department of Agriculture, University of Oxford, and Agricultural Research Council 



Unit of Experimental Agronomy 



During the last five years research has been proceeding at Oxford on the 

 interconnected problems of the factors governing the absorption of growth 

 regulators and their influence in turn on the absorption of other compounds. 

 Investigations concerned with the uptake of 3-indolylacetic acid have 

 already been published (Reinhold, 1954) and this paper summarizes some of 

 the work which has been proceeding on similar lines with 2:4-dichloro- 

 phenoxyacetic acid. Initially, the effects of this growth regulator on the 

 absorption of nitrogen, phosphorus, and potassium were investigated by 

 H. M. Squire(Part II Chemistry Thesis, 1952) and continued by E. F. Henzell 

 (D. Phil. Thesis, 1955). Complementary experiments relating to mechanisms 

 controlling the uptake of 2:4-dichlorophenoxyacetic acid were started by 

 W. R. Birch (B.Sc. Thesis, 1955) and these are now being extended by 

 G. Sen and C. C. McCready. 



A number of workers, for example Nance (1949), Asana, Verma, and 

 Mani (1950), Klingman and Ahlgren (1951) and Freiberg and Clark (1952), 

 have reported that phytotoxic doses of 2 :4-dichlorophenoxyacetic acid 

 depress the absorption of nitrogen by a number of different species. Rhodes, 

 Templeman, and Thruston (1950) and Rhodes (1952) have found that the 

 effects of 2-methyl-4-chlorophenoxyacetic acid on the mineral uptake and 

 mineral content are dependent on both the experimental conditions and the 

 species. Thus, when tomatoes were grown in culture solution containing the 

 growth regulator, the potassium uptake and the potassium content of the tops 

 and lower stems were depressed but potassium accumulated in the roots; 

 the trends for phosphorus and nitrogen were similar but less marked. If on 

 the other hand the application of the growth regulator was made as a spray 

 to the shoot, then on the basis of 'residual dry weight' the total uptakes of 

 nitrogen and phosphorus were reduced, but there was no suppression of the 

 absorption of potassium, calcium, or magnesium. 



In the majority of these investigations the plants were either grown in the 

 open or in a greenhouse and the observations were recorded over consider- 

 able periods subsequent to treatment with the growth regulator. In con- 

 sequence, comparison is rendered difficult because of fluctuations in the 

 environmental conditions and ontogenetical drifts in the composition of 

 the plants. In order to eliminate these variables clonal populations of the 

 aquatic plants Lemna minor and Salvinia natans were selected and grown under 

 constant conditions of light (continuous illumination of 275 or 



253 



