Physiological and Anatomical Effects 129 



tween the stinuilalioii of respiration and the stimulation of growth. 

 Assuming that the energy of respiration must ultimately be responsible 

 for growth, one would hope to find some sort of proportionality exist- 

 ing between them. Commoner and Thimann (1941) found that con- 

 centrations of iodoacetate which completely inhibit growth, inhibit 

 respiration only approximately 10 per cent. This raises the interesting 

 possibility that the respiratory functions which are involved in growth 

 may be only a small part of the overall respiration regime. Responses 

 other than growth very frequently do not correlate with respiratory 

 changes. Several instances of the lack of correlation have been cited 

 by Smith (1951) and include the inhibition by auxins of nitrate up- 

 take by roots and inhibition of germination and root growth. A corre- 

 lation between respiratory and growth responses to auxin was 

 demonstrated for each of several auxins by French and Beevers (1953). 

 Sample data for responses to indoleacetic acid are given in tigure 58, 

 from which it can be seen that the ranges of auxin levels which pro- 

 mote tliese two functions are roughly similar. Although small growth 

 responses coidd be obtained without a measurable reflection in respira- 

 tion, the peaks of both functions appear at the same auxin level. 



A particularly interesting suggestion concerning the relation of 

 respiration responses to growth responses has been recently made 

 (French and Beevers, 1953). Simultaneous measurements of respiratory 

 and growth responses showed that respiration was promoted by some 

 substances which could not produce growth promotions. This led to 

 the suggestion that a more indirect connection between respiration 

 and growth may exist. It was proposed that the respiratory promotion 

 by auxins might be a consequence of the growth promotion rather 

 than its cause. In this concept, respiration produces energy which is 

 captined in high-energy phosphate bonds, and this energy may then 

 be utilized for growth. Auxins may stimulate growth resulting in a 

 utilization of the phosphate bonds. Respiration may then proceed 

 faster because of the presence of more phosphate acceptors. Non- 

 auxins like 2,4-dinitrophenol can produce the same respiratory pro- 

 motions by uncoupling the phosphorylase system from growth. 

 According to this idea, then, auxins increase respiration by utilizing 

 the products of phosphorylation in growth, whereas non-auxins like 

 dinitrophenol increase respiration by stripping off the products of 

 phosphorylation without utilizing them in growth. A similar relation 

 between the effects of auxin on respiration and water uptake has 

 been suggested by Bonner et al (1953). 



Some possible means by which respiratory energy may be utilized 

 for growth are discussed in chapter VIII. 



