DYNAMICS OF AMINO ACIDS IN PLANTS 665 
(The increased rate of synthesis would have to occur in the stem, as leaf differences 
are relatively minor.) The correlation with shikimic acid metabolism is an obvious 
one, as both the phenolic acids and the benzenoid aromatic amino acids arise from 
shikimate. A hypothesis we are pursuing at present is that of boron control of 
membrane permeability, possibly the chloroplast membranes, allowing the diffusion 
of sedoheptulose, or even of its phosphate. If shikimate formation was controlled 
normally by one of the metabolic steps subsequent to sedoheptulose formation, its 
excess in the cytoplasm by virtue of — B membrane transmission would result in 
excess phenols and amino acids. However, this would also require translocation of 
these amino acids down the stem, and, at present, there is no satisfactory evidence 
of appreciable movement of amino acids out of leaves. 
In fact, the question of tryptophane synthesis in leaves of higher plants is itself a 
troubled one. Thus, in our early days, we were never able to demonstrate the forma- 
tion of radiotryptophane by the feeding of CO, to excised soybean leaves, although 
phenylalanine was identified readily and shown to be labeled uniformly’. It was 
possible, of course, that tryptophane was formed in the roots and translocated, as 
needed, to leaves. Furthermore, it had been reported previously” that the level of 
TABLE 1X 
RADIOACTIVITY OF TRYPTOPHANE FROM SOYBEAN LEAVES FED CO, 
From PERKINS AND ARONOFF, unpublished results. 


Free try, relative Protein try, relative 
specific activity specific activity 
Sample ———— 
(counts|/min|mg) 

Leaf, young, excised 9.2 93.1 
Leaf, mature, excised 7-9 16.9 
Leaf, young, intact 2.8 38.2 
Leaf, mature, intact 16.8 96.1 
Root, mature, intact Lie 10 14.9 

tryptophane in legumes was a function of their boron content. We therefore repeated 
our earlier studies with relatively massive CO, feedings to both mature and young 
leaves, excised and intact, and examined these, as well as the mature root, with 
special regard to tryptophane, both as a free amino acid and as part of protein. The 
results (Table IX) demonstrate that excised leaves do, indeed, contain radiotryp- 
tophane, though in rather meager amounts. Of course, the radioactivity could well 
lie in the alkyl portion of the molecule, and thus bear no relation to the shikimate 
problem. The answer lay in the degradation of the molecule to some fragment of the 
indole nucleus. Because of the paucity of activity, we limited ourselves to a reaction 
known to yield demonstrable product, namely the degradation of tryptophane to an- 
thranilic acid by liver homogenates! 4. Unfortunately, the requirements for puri- 
fication of the anthranilic acid involved continuing losses, and only the preparations 
from the two tryptophanes of highest specific activity gave anthranilic acid with 
reasonable activity. Even these were so low that all one can say was that highly puri- 
fied anthranilate was active to a level roughly corresponding to a uniform distribu- 
References p. 666 
