THIMANN, BONNER, AND CHRISTIANSEN lOI 



merely kept in water, that is, when little elongation takes place, but all 

 three acids are used up rapidly when the sections grow. As we shall 

 see below, these acids are indeed not the only metabolites which are con- 

 sumed in the process of growth. Furthermore it is clear that when growth 

 is inhibited by arsenite, the consumption, especially of malate and 

 pyruvate, is prevented. 



Now the metabolism of the organic acids is interrelated with many 

 aspects of the oxidative metabolism of tissues so that the consumption of 

 organic acids in growth, and their preservation when growth is inhibited, 

 would indicate that growth and inhibition involve deep-seated changes 

 in metabolism. Yet it is a curious fact that when growth is promoted by 

 auxin the total oxygen consumption is not increased detectably in the 

 coleoptile,* and only 15 per cent in the pea; correspondingly also, 

 growth can be inhibited without detectable decrease in oxygen consump- 

 tion. In the case of inhibition by fluoride there is even a small increase in 

 oxygen consumption. These considerations led us to make a more careful 

 study of the changes that go on during inhibition. For this purpose we 

 have used a growth inhibition of 50 per cent as a reference point because, 



(a) this is achieved with relatively low concentrations of inhibitors, and 



(b) it takes place with only minor changes in respiration rate. Pea stem 

 sections were used rather than coleoptiles because they do not require 

 added sucrose for growth. The three inhibitors, iodoacetate, arsenite, 

 and fluoride were all used. 



We have previously reported (4) that when growth is inhibited re- 

 ducing sugars disappear. They disappear steadily with time, whether the 

 sections are growing or not, but in the presence of inhibitor (at a 

 concentration sufficient to reduce growth by 50 per cent) their disap- 

 pearance is accelerated. Arsenite, iodoacetate, and fluoride all had the 

 same effect. Since the oxygen consumption of the sections is not in- 

 creased, the polysaccharides were determined. However, there was no 

 significant change in any of the cell-wall constituents, and the sections 

 do not contain starch. The sugars, therefore, were neither being oxidized 

 nor polymerized. An examination of the neutral ether-soluble material 



*There is some difference of opinion on this. Van Hiilssen (1936), J. Bonner 

 (1936), and Commoner and Thimann (1941) found no increase, while Berger, 

 Smidi, and Avery (1946) and J. Bonner (1949) record increases of 20—25 per cent 

 when physiological concentradons of indoleacetic acid are added. Kelly and 

 Avery (1949) found that 2,4-D increased respiradon in concentrations below the 

 toxic level. 



