The kinetics of auxin-induced growth 



Equilibria between the various bound forms of phenoxyacetic acids. 



2:4-diCl- 

 Cl 



'0 ^H 



ni 



uz 



p-Cl- 



Clf^^^^ 



-0^ -H 



ni 



02 



cif^=^ 



Cl H 



o-?-c^° 



JU. 



ni 



n2 



ni 



70 



Cl^^^ 



Cl 



Cl 



0-^c: 



,^^ 



A 



02 



17 

 Cl 





40 



V-"'" 



1 



02 



40 



■Cl- 



^^^ci°^c-°^ 



cr°> 



^^^ 



Cl 



ni 



02 



ni 



H 



I 

 ^c. 



0" 1 "c^ 







02 



1 . 14 70 



Figure 7. Distribution of auxin-receptor of the Avena coleoptile section among the varied forms of 

 auxin-receptor complex. Data for phenoxyacetic acids. The distributions are calculated for the optimal 

 concentration of each growth substance, sifter Foster (1953). 



We may now determine the ratio of any one form of ES to £'totai i^ terms of 

 the several equihbrium constants K, and auxin concentration {S). For 

 example, the expression relating growth active -fi'.S'i 2 to -Etotai is of the form 



(^•^1.2) 



.(15) 



We can now solve equation (15) for the numerical value of £'6'i g/^^totai foJ" 

 any given value of auxin concentration. Let us use that concentration of 

 2:4-D which yields maximum growth rate, i.e. 6xlO-*^M. Expressions 

 similar to that of equation (15) can be derived for each of the individual ES 

 complexes and can be similarly solved. The results, summarized in Figure 7, 

 indicate that for coleoptiles in steady-state growth in the optimum concentra- 

 tion of 2:4-D, approximately 70 per cent of receptor endties are combined in 

 growth active £^'1,2 at any one moment, and that the remainder are distri- 

 buted between varied growth inactive precomplexes, particularly the sinlgy 

 attached (through the carboxyl group) ES-^^. 



303 



