THE MODE OF GROWTH ACTION OF SOME 

 NAPHTHOXY COMPOUNDSf 



H, BuRSTROM and Berit A. M. Hansen 

 Botany Laboratory, University of Lund 



INTRODUCTION 



It has been shown in a previous communication (Burstrom, 1955) that 

 naphthalene acetic and naphthoxyacetic acids increase and decrease root 

 elongation according to a fairly complicated pattern. 



By testing combinations of these acids it was also shown that some effects 

 of low concentrations of the 2-substituted acids were physiologically 

 independent of the others, and that, at high concentrations, the acids can 

 exert toxic effects which complicate the assessment of real growth activities. 

 Furthermore, 1 -naphthalene acetic and 2-naphthoxyacetic acids inhibited 

 root elongation and were classified as auxins, whereas 2-naphthalene acetic 

 and 1 -naphthoxyacetic acids increased root elongation and antagonized the 

 two others. They should be classified as root auxins according to Hansen's 

 (1954) terminology; they cannot a priori be called anti-auxins in the sense of 

 the semi-official nomenclature (Tukey et al., 1954) because it has not been 

 shown conclusively that they act as competitive inhibitors of auxin. It is 

 also convenient for other reasons to use a term which does not anticipate a 

 special mode of action. 



Of the two supposed auxins, 2-naphthoxyacetic acid has unanimously been 

 classified as an auxin in the literature (see Hansen, 1954); Street (1955), 

 however, has questioned whether the root-growth effect of 1 -naphthalene 

 acetic acid is physiologically of the same kind. 



A tentative explanation of why these two acids are auxins and the other 

 two are not has been given by Jonsson (1955). This implies that they are 

 auxins because the side-chain can form a pseudo-ring in the plane of the 

 naphthalene ring with the carboxyl near the centre of the compound ring 

 system. For sterical reasons this is impossible with the other two acids. 

 This provides an amendment to the commonly accepted structural 

 requirements of auxins, giving a reason for the different activities of these 

 four acids. 



In order to test this explanation, experiments have been conducted with a 

 number of chlorine derivatives of the two auxins, all of which were prepared 

 and kindly suppHed by Dr. Jonsson. The tests with the derivatives of 

 2-naphthoxyacetic acid have led to some rather unexpected results, which 

 may be of general importance for elucidating the mode of action of these 

 compounds. 



t This paper was read at the Conference by H. Burstrom. 



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