290 MISCELLANEOUS NITROGEN AND SULFUR COMPOUNDS 



These include the amino acid tryptophan and many alkaloids. Besides these there are 

 several other indole compounds which do not fit well into any large category but are too 

 important to be ignored. Indole itself is partly responsible for the odor of jasmine flowers. 

 A review of indole derivatives found in plants has been presented by Stowe (39). 



Of most interest in plant physiology are the compounds closely related to indole-3- 

 acetic acid, the most important natural auxin. Other natural indole derivatives whose 

 structures are given below have auxin activity similar to that of indole -3 -acetic acid, but 

 it is generally believed that they are active only after being enzymatically converted to 

 indole -3 -acetic acid. 



CHgCOOH f^^ jrCHgCN 



CO 



indole-3-acetic acid indoIe-3-acetonitrile 



Co 



CHgCH 



indole -3 -acetaldehyde 



More complex derivatives such as indole -3 -acetylaspartic acid (40) and l-(indoIe-3- 

 acetyl)-i3-D-glucose (41) have also been found. All of these compounds are rather un- 

 stable and occur in plants at very low concentrations, so that isolation of them represents 

 a formidable problem. The general references should be consulted for information about 

 such methods. The indole -containing auxins have been separated and identified by paper 

 chromatography and electrophoresis according to methods developed by several different 

 workers (42, 43, 44), Stowe and Thimann (45) studied 35 different indole compounds and 

 found the best all-round solvent for paper chromatography to be jso-propyl alcohol/28% 

 NH4OH/H2O (8: 1: 1). Various spray reagents have been used to detect these compounds on 

 chromatograms. Best-known is the Salkowski reagent (0.001 M ferric chloride in 5% per- 

 chloric acid) which gives a red color. Compounds with auxin activity can of course be 

 located by eluting sections of the chromatogram and testing the eluates for activity. 



The pathways of indole -3 -acetic acid biosynthesis and breakdown are not well-clari- 

 fied. Tryptophan is generally believed to be an obligatory precursor, and evidence sum- 

 marized by Gordon (46) suggests that indole -pyruvic acid and indoleacetaldehyde are in- 

 termediates. Other compounds such as the nitrite are probably side issues rather than 

 normal intermediates. Breakdown of indoleacetic acid is oxidative, catalyzed by indole- 

 acetic acid oxidase or a peroxidase. Auxin destruction has been reviewed by Ray (47). 



Whereas the indole auxins are of great interest in plant physiology, other indole 

 compounds found in plants show striking physiological effects on animals. These are 

 tryptamine and derivatives of it such as 5-hydroxytryptamine (serotonin). 



