CLARA M. SZEGO 159 



is the extension of various modifications of this postulate to the plant auxins 

 by a number of workers (cf. 2, 5, 17, 22, 42). Bonner and associates have indeed 

 suggested (cf. 5) that the multiplicity of growth and metabolic responses of 

 plant cells to auxin is predicated upon a fundamental, primary one — namely, 

 the facilitation of a water transport system which leads to active water accu- 

 mulation in the auxin-stimulated plant cell. The state of this subject is ex- 

 tremely controversial in terms of whether the profound water shift is a primary 

 reaction, or secondary to other phenomena (cf. 2, 17, 22). The observations 

 presented at these meetings by Skoog (30), on the potentiating effect of certain 

 amino acids on auxin- and kinetin-induced growth may, similarly, reflect 

 enhancement of a translocation mechanism for these substrates which partic- 

 ipate in secondary anabolic reactions in the target cell. 



While it is most unlikely that the multifarious effects of the several plant 

 and animal hormones of grossly dissimilar configuration, elicited on widely 

 divergent target cells, may be explained by a single, unified hypothesis, it is 

 tempting to see how far the analogies can be carried in the light of existing data. 



HORMONAL COMPLEXES WITH PROTEIN 



It would seem self-evident that interactions of the hormones with appro- 

 priate, relatively specific, protoplasmic receptors must lie at the root of their 

 influence on the metabolic activities of their several and specific target struc- 

 tures. This consideration would appear axiomatic in view of the extremely low 

 order of magnitude of the dosage requirements, and is in line with the general 

 concept advanced time and again for the mode of action of many highly potent 

 drugs (cf. 7, 10). Such combinations could occur at the target cell or elsewhere, 

 and result in the new biochemical entity which 'triggers' the response complex, 

 not dissociated from the consequences to specific permeability phenomena 

 discussed above (cf. also 24, 36). 



Here again, there are a number of signposts which indicate that a broad gener- 

 alized mechanism may exist among hormonally active compounds of grossly 

 dissimilar configuration. The affinity of insulin for proteins of the muscle cell 

 to which it appears to be attached before exerting its characteristic effects on 

 glucose transfer (cf. 31), the occurrence of circulating thyroid hormone in 

 association with a specific a-globulin (cf. 3), the demonstration of auxin-protein 

 complexes in the plant (cf. 17), some of which require high-energy phosphate 

 for their formation (29), all appear to point in this direction. Attention may 

 also be directed to a preliminary observation by Saffran and Bayliss (27), who 

 noted persistence of the /;/ vilro effectiveness of ACTH on adrenocortical 

 steroid biosynthesis, after initial exposure followed by rinsing of the tissue in 

 buffer. This finding, by analogy to that of Stadie and his group with insulin 

 (cf. 31), may likewise represent combination of the hormone with target cell 

 protein. 



A considerable literature is available on the in vivo and in vitro interaction 



