OCCURRENCE OF FREE AMINO ACIDS — PLANTS 43 
SOME RECENTLY-CHARACTERIZED AMINO ACIDS 
FROM PLANTS 
L. FOWDEN anp D. O. GRAY 
Department of Botany, University College, London (Great Britain) 
During the last 15 years a gradual re-appraisal of the overall character of the free 
amino acid pools of plants has been necessary. In this time the number of amino and 
imino acids recognized as plant constituents has increased from some 25~30 (mainly 
those present also in proteins) to about roo. Each yea~ several new acids are isolated 
and characterized and at present there seems to be no foreseeable limit to the number 
that will be recognized ultimately. Indeed, the situation regarding the amino acids 
of plants is approaching rapidly in complexity that encountered with the alkaloids. 
Several reviews of this subject are available, the most recent being that of FOWDEN’, 
which cites the earlier accounts. The present paper attempts to augment these with 
brief descriptions of acids either reported within the last year or at present under 
investigation in our laboratory. 
Although the amount of available information on plant amino acids is increasing 
continually, it is still not possible to make many generalisations regarding their 
distribution. The protein amino acids are present normally in the free amino acid 
pools but in relative amounts that are very different for different species, or even for 
different organs of the same plant. For many of the other acids, the distribution 
within and between families is apparently haphazard. Some acids do seem to be 
especially characteristic of certain plant families, e.g. citrulline for the Cucurbitaceae, 
and azetidine-2-carboxylic acid for the Liliaceae (FOWDEN AND STEWARD?), whilst 
callus-type growth sometimes results in a characteristic production of particular 
acids, e.g. lysopine in crowngall tissue from salsify (Scorzonera hispanica), tobacco 
(Nicotiana tabacum), Virginia creeper (Parthenocissus tricuspidata), and Jerusalem 
artichoke (Helianthus tuberosus) (BIEMANN et al.3), and hydroxyproline, present in the 
protein, of rapidly growing tissue explants of carrot root and potato tuber (STEWARD, 
THOMPSON AND PoLLarD!). The largest proportion of the newer acids have been 
isolated from members of the families Liliaceae, Leguminosae and Cucurbitaceae. 
The metabolic interrelationships of the majority of the more recently characterized 
acids are shrouded with uncertainty ; few of them have been integrated into metabolic 
schemes that may be regarded as part of the basic pattern of nitrogen metabolism 
of plants. 
ACIDS ISOLATED RECENTLY FROM MACROSCOPIC PLANTS 
Isolations of three new sulphur-containing amino acids have been reported. S-(2- 
Carboxy-1-methylethyl)-1-cysteine (I) was obtained from seeds of Acacia mullefolia 
and Acacia willardiana (GMELIN AND HreTALA®), whilst VIRTANEN® has reported 
that S-n-propyl-t-cysteine sulphoxide (II, dihydroalliin) occurs in onion bulbs 
(Allium cepa). Chondrine (III, 1-1,4-thiazan-3-carboxylic acid r1-oxide) has been 
References p. 53 
