Chemical structure and biological activity 



inactive in themselves, as is the 1 : 3-dichloronaphthoxyacetic acid, or belong 

 to the same type of growth compounds as the 1-chloro acid. The growth- 

 decreasing effect of auxins should be physiologically independent and located 

 in the second growth phase. This is supported by the observation that 

 the 1-chloronaphthoxyacetic acid does not influence the behaviour 

 of the unchlorinated acid. 



On the other hand, it is clear that anti-auxins can be exchanged for the 

 native auxin and act as growth regulators in this way. This has been deduced 

 by means of the kinetic methods introduced by McRae and Bonner (1952), 

 by Ingestad (1953), and shown analytically by Fransson and Ingestad (1955) 

 on coleoptiles. A way out of this dilemma is to make the rather natural 

 assumption that these compounds all act on both phases of the cell elongation, 

 either by competing with the native auxin or by virtue of their own inherent 

 activity. Owing perhaps to minor details in structure, the effect in one or 

 the other system dominates, making one substance an auxin assumed to 

 inhibit predominately growth phase II, another a root auxin when the action 

 on phase I dominates, or a third substance an anti-auxin if it acts mainly by 

 competing with natural auxin. 



Such details in the activity do not show up in the net elongation of cells 

 or organs, which is the usual observation recorded, but for correlating 

 structure with activity it may be necessary to pay due regard to the different 

 ways the compounds can act on the growth mechanism. 



REFERENCES 



BuRSTROM, H. (1942). The influence of heteroauxin on cell growth and root develop- 

 ment. Ann. agric. Coll. Sweden, 10, 209. 

 BuRSTROM, H. (1954). Studies on growth and metabolism of roots. XI. The influence 



of auxin and coumarin derivatives on the cell wall. Physiol. Plant. 7, 548. 

 BuRSTROM, H. (1955). Evaluadon of the growth activity of naphthalene derivatives. 



Physiol. Plant. 8, 174. 

 Fransson, P., and Ingestad, T. (1955). The effect of an antiauxin on the indoleacetic 



acid content in Avena coleoptiles. Physiol. Plant. 8, 336. 

 Hansen, B. A. M. (1954). A physiological classification of 'shoot auxins' and 'root 



auxins'. I-II. Bot. Notiser 230, 318. 

 Ingestad, T. (1953) . Kinetic aspects on the growth regulating eff'ect of some phenoxy 



acids. Physiol. Plant. 6, 796. 

 Jonsson, a. (1955). Synthetic plant hormones. VIII. Relationship between 



chemical structure and plant growth activity in the arylalkyl, aryloxyalkyl, and 



indolealkylcarboxylic acid series. Svensk kern. Tidskr. 67, 166. 

 McRae, D. H., and Bonner, J. (1952). Diortho substituted phenoxyacetic acids as 



antiauxins. Plant Physiol. 27, 834. 

 Meeuse, a. D. J. (1942). A study of intercellular relationships among vegetable 



cells with special reference to sliding growth and to cell shape. Rec. Trav. bot. 



need. 38, 18. 

 RuFELT, H. (1954) . Influence of growth substances on the geotropic response of roots. 



Physiol. Plant. 7, 141. 



Street, H. E. (1955). Factors controlling meristematic activity m excised roots. 

 VI. Effects of various 'antiauxins' on the growth and survival of Lycopersicum 

 esculentum, Mill. Physiol. Plant. 8, 48. 



TuKEY, H. B., Went, F. W., Muir, R. M., and Overbeek, J. van (1954). Nomen- 

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