Oxidants, Antioxidants, and Groioth Regulation 347 



cotinyl hydrazine (isoniazid) and other hydrazines; and by tyraminc 

 and mescaline. The phenylethylamines promoted growth only 20 

 to 25 per cent, but the other compounds, all more efficient anti- 

 oxidants, increased growth 90 to 150 per cent. 



In the two section tests, extensive comparisons were made between 

 lAA and a number of other antioxidants as elongation promoters 

 (Table 1). Cucumis elongation is promoted to approximately the 

 same degree by lAA, pyrrole, skatole, serotonin, and diphenylhy- 

 drazine. The other compounds listed show one-half to three-quarters 

 of lAA activity. Taraxacwn elongation is more specific for lAA, but 

 even the weakest growth promoters were one-fifth as active as lAA. 



When chemical and biological activities are considered jointly, 

 it is apparent that substances of different constitution but high anti- 

 oxidant efficiency, show qualitatively similar biological effects (Table 

 2). Percentage deviations from appropriate controls have been tabu- 

 lated to show both the direction and magnitude of the effects. 



Although some correlation may be found in comparing specific 

 chemical and biological tests, experience has shown that this is not 

 generally true. We must recognize that, ideally, antioxidant activity 

 is a measure of electronic behavior whereas over-all biological effec- 

 tiveness also depends upon thermodynamic and geometric properties 

 which are the determinants of transport and localization. 



Lignification is one of the processes which characterize maturation 

 and cellular senescence in the green plant (21,23). The experimental 

 biosynthesis of lignin proceeds through a radical initiated chain 

 mechanism and offers a model for the natural process. Experimentally, 

 quinones accelerate lignin synthesis, a role consistent with their ap- 

 pearance in differentiating tissues. In contrast, various metabolites, 

 especially DPN, are powerful inhibitors of lignin formation. Exten- 

 sive lignification is thus indicative of cellular oxidation-reduction 

 imbalance. It can be "forced" upon young cells experimentally but 

 is most pronounced in xylem differentiation where it accompanies 

 or is accompanied by protoplastic degeneration. lAA and other anti- 

 oxidants both inhibit lignin synthesis and promote elongation. The 

 growth-promoting activities of some biological agents acting as anti- 

 oxidants in their proposed protective and metabolic roles may be 

 reflected in their ability to delay the onset of lignification and at- 

 tendant deteriorative oxidative processes. 



OXIDANT-ANTIOXIDANT INTERACTIONS 

 IN GROWTH 



General Considerations 



Application of reductants accelerates regeneration whereas callus 

 formation is inhibited by oxygen and other oxidants (28). Cysteine, 

 Co+2 salts, propyl gallate, and sympathomimetic amines have been 



