Oxidants, Antioxidants, and Growth Regulation 345 



of oxidation, more oxidized substances may be physiologically inactive 

 or even inhibitory. Oxindoles are representative of the inactive state; 

 quinones as thiol reagents and H-abstractors serve as harmful oxidants. 

 Quinonoid substances have been implicated in normal cessation of 

 growth and onset of differentiation in plants (18, 30). Quinones are 

 known experimentally for their antimitotic and radiomimetic activities 

 (19). 



Experimental Studies 



Methods employed in evaluation of antioxidants may be found in 

 published or forthcoming accounts. The experimental oxidation 

 systems used include iodide-HoOo (26,27); eugenol, peroxidase- 

 HoOo (22); eugenol, celery vascular tissue-HoOo (21,24); and to 

 a lesser degree iodide, peroxidase-HoOo and pyrogallol-Oo (23). 

 Measured oxidation products are, respectively, iodine; dimerization 

 product; lignin; and in the last two systems iodine, once again, and a 

 phenol polymer-polyquinone mixture. 



The growth responses studied included germination of onion 

 {Allium cepa, 'Yellow Globe'); elongation of turnip radicle {Brassica 

 rapa, 'Purple Top White Globe'); elongation of cucumber hypocotyl 

 sections (Cuciimis sativus, 'Improved Long Green'); and elongation of 

 flower stalk sections from Taraxacum officinale. All test materials 

 were cultured in solutions buffered at pH 6.65 (0.066Af phosphate) 

 under 50 footcandles constant illumination (22, 27). 



The chemical test systems have been used to demonstrate anti- 

 oxidant activity in the following compounds: Indoles, including in- 

 dole, indoline, methyl- and phenylindoles, lAA; other indolealkanoic 

 acids, 5-hydroxy-IAA, tryptamine, tryptophane, serotonin, and car- 

 bazole; Pyrroles, including pyrrole, methyl- and phenylpyrroles, the 

 bile pigments, and pyrrolidine; Hydrazines, including hydrazine and 

 its salicylyl-, malonyl-, maleyl-, isonicotinyl-, aryl-, and alkyl- deri- 

 vatives; Diazines and miscellaneous heterocyclic compounds, including 

 purine, mercapto-purines, benzimidazole, pteridines, and benzthio- 

 phene; Amities, including alkylamines, phenylethylamines, and aryl- 

 amines; Aryloxy compounds, including diphenylether, benzofuran, 

 anisole, thyronine, and iodothyronines (thyroxine, for example); and 

 various thiols, phenols, ascorbic acid, and Co^^ salts. 



Activity-constitution relations have emerged in some instances 

 (23, 27). Thus antioxidant efficiency among the indoles is reduced 

 by electron-withdrawing groups, as in oxindole, oxindone, or indole 

 aldehyde. Less marked reduction results from 3-substitution. Both 

 deactivating effects are illustrated in the series indole > skatole>> 

 indoleformic acid. Deactivation may also be effected by decreased 



