Oxidants, Antioxidants, and Growth Regulation 343 



Oxidant toxicity - the physiological consequences of antioxidant 



action. 



1. Their essential role in metabolism notwithstanding, oxygen 

 and other oxidants attack essential cellular components, and 

 bring about a cumulative loss in essential functions. 



2. Ontogeny (the developmental sequence of the individual) be- 

 gins with an excess of antioxidants, a relatively low oxygen 

 tension, and frequently, a low oxygen demand. 



3. As development proceeds, oxidized substances accumulate. The 

 rate of oxidant accumulation will vary with the environmental 

 oxygen supply. Increase in environmental oxygen may be 

 gradual, but frequently involves a discontinuity such as hatch- 

 ing or birth. 



4. As development proceeds further in continuous contact with 

 oxygen, oxidized cellular components accumulate, increasing 

 the ratio oxidant/antioxidant (or electron acceptor /electron 

 donor). As the acceptor-donor balance shifts toward the oxi- 

 dized state, cellular activities are altered: 



a. A loss in proliferative capacity - decreased mitotic activity 

 - stabilized cell populations in tissues and organs. Differ- 

 ential oxidant tolerance results in unequal cessation of 

 suppression of cell division. 



b. Certain cellular growth activities may persist in the more 

 oxidized state, or may be favored at a higher acceptor-donor 

 ratio than cell division. Cell enlargement, especially in 

 plants, is indicated here. 



c. Further shifts in the acceptor-donor balance terminate all 

 growth processes, but allow maintenance of the individual 



cell. 

 5. Maintenance of the nongrowing cell, tissue, or organism char- 

 acterizes the prematuration state. 



a. Prematurity is an unstable transition state. The acceptor- 

 donor balance either attains a plateau or lies within range 

 of values analogous to a range of maximum buffering 



capacity. 



b. Further maturation processes may entail chemical changes 

 indicative of the progressive domination of the cell by oxi- 

 dants and oxidation. Examples are melanization and lignifi- 



cation. 



c. Initiation of major secondary chemical changes may shorten 

 the transition state leading to rapid loss of function. 



6. Beyond the efficient "buffer range," accumulation of oxidative 



