DYNAMICS OF AMINO ACIDS IN PLANTS 663 
TABLE Vil 
DISTRIBUTION OF RADIOACTIVITY IN SOYBEAN LEAF FED @CO, 
IN THE DARK 
From RACUSEN AND ARONOFF, unpublished results. 



Fraction % Activity 
80% aq. ethanol solution 70.8 
a) cation 54.0 
b) neutral + anion 16.8 
80% aq. ethanol residue 28.3 
a) cation 25.7 
b) neutral + anion 2.6 
Crude fiber (5.5 mg) 0.9 

the amounts of these amino acids in the protein of young leaves is of the order of 
10-fold more than in mature leaves (37.5°% compared to < 5%); and, secondly, the 
free amino acids of young leaves are present only as traces, virtually non-existent, 
whereas in mature leaves they constitute an analytic amount, though totaling less 
than 5%. Thus, young leaves have not only a greater capacity for producing the 
essential amino acids, but for incorporating them more completely into protein. 
TABLE VII 
DISTRIBUTION OF RADIOACTIVITY IN CATION FRACTION 
OF SOYBEAN LEAF FED 1!4CQO, 20 H IN THE DARK 
From RACUSEN AND ARONOFF!?, 


% of cation activity 

Amino acid 4 5 ; 
: : Protein amino 
Free amino acids 

acids 
Asp 6.8 | 
Asp-NH, ayer 4p ese 
Glu 13.5 | 
Glu-NH, toy" Ait sae 
Seq 6.8 14.8 
Gly +1 31.0 
Ala ae 4-9 
Arg 3 em 0.0 
Others 235 ale 
* Unknown; not urea. 
** Phe, tyr, pro, leu, arg; altogether less than 
5% of total cationic. 
Amino acids and boron deficiency 
Experiments on the biochemical function of boron in plants demonstrated that 
even severe deficiency symptoms did not affect appreciably the rate (per unit area 
of leaf) or qualitative aspects of photosynthesis. Quantitatively, however, the anionic 
References p. 666 
