182 Fundamentals of Auxin Action 



growth might follow. Northen also pointed out that if dissociation 

 activities are carried to the extreme, the stimulation effects upon 

 enzymes in respiration would be reversed by dissociation of essential 

 constituents from enzymes, and he proposed that this may be the 

 nature of inhibition of growth by auxin and the concomitant inhibi- 

 tion of respiration. 



If the auxin-induced decrease in cytoplasmic viscosity is due to a 

 hydration of the protein constituents, one might expect an increase 

 in the water of hydration in cells exposed to auxin. Levitt (1948) has 

 not been able to find such an increase. A further criticism is found 

 in the work of Blank and Deuel (1943) who were unable to detect 

 protoplamic viscosity changes at some of the lower auxin concentra- 

 tions even though growth was still being stimulated by the auxin. 



Another theory of auxin action through enzymic mechanisms has 

 been proposed by Thimann (1951). He points out several lines of 

 evidence indicating that a sulfhydryl containing enzyme may be very 

 intimately involved in growth and that poisons which attack sulf- 

 hydryl enzymes also antagonize auxin action. He has suggested that 

 auxins may act, not as enzyme-activating agents, but as agents protect- 

 ing growth enzymes from inactivation. On this basis, the structural 

 requirements for an active auxin may be explained on the basis of 

 structural specificity to antagonize enzymic inhibitors. 



Another suggestion as to the nature of auxin action in growth has 

 been made by Bonner (1949) and expanded by Bonner and Bandurski 

 (1952). They cite a considerable amount of indirect evidence to sug- 

 gest that auxin may serve in some manner to couple or mesh together 

 the respiratory processes with the growth processes. By this scheme 

 auxin would act in some role which would make the energy formed in 

 respiration available to the growth processes. They point out several 

 indications suggesting the participation of auxin in phosphorylation 

 and energy transfer reactions. Such indications may be listed as (1) 

 the ineffectiveness of auxin in the presence of agents which uncouple 

 phosphorylations (such as arsenate and dinitrophenol), and (2) the 

 evidence that phosphorylation reactions commonly limit growth. The 

 suggestion is a very interesting one, but needs some direct evidence 

 to support it. 



THEORIES OF OSMOTIC EFFECTS 



In the process of growth, increases in cell volume may be largely 

 accounted for on the basis of water uptake. Consequently a great deal 

 of attention has been given to the water uptake mechanism as a 

 possible means of describing growth in its simplest form. The uptake 



