728 



S. Tonzig and E. Marre 



Table 1 . The effects of ascorbic acid (AA) on growth and internal contents of AA 

 and dehydroascorbic acid (DHA) in pea internode segments. (E. Marre and G. Laudi, 

 unpublished.) 



* Medium buffered with 0.05 M phosphate, pH 6. For experimental conditions 

 see (5). 



Glutathione Oxidation/Reduction Equilibrium 



In the pea internode segments, AA at growth inhibiting concen- 

 trations consistently increased the ratio of oxidized to reduced gluta- 

 thione (7). This effect seems quite interesting, as it has been shown 

 that the oxidation-reduction state of glutathione is an important fac- 

 tor in growth regulation (6, 7). 



It has to be emphasized that all of these physiological parameters 

 (plasma viscosity, water holding capacity, respiration, reduced to oxi- 

 dized glutathione ratio, as Avell as growth by cell extension and cell 

 division), are also influenced — under identical experimental condi- 

 tions — by auxins. However, the auxin induced effects are always op- 

 posite in direction to those induced by treatment with AA. 



METABOLIC CHANGES ACCOMPANYING THE EFFECTS 



OF ASCORBIC ACID ON GROWTH AND 



RELATED PROCESSES 



The fact that AA seems to behave, at least in most cases, as an 

 antagonist of auxins, suggested the possibility of some kind of bio- 

 chemical competition between the two types of substances or between 

 their active derivatives. This hypothesis appears consistent with the 

 results of experiments showing that the amount of free (easily ex- 

 tractable) auxin increases, while bound auxin decreases in pea stem 

 segments treated with AA. Moreover, diffusion of auxin from isolated 

 oat coleoptile sections was accelerated by treatment with AA (24). 



A different approach to the problem of the mechanism of action 

 of AA was suggested by some investigations on its fate when ex- 

 ternally supplied. Moreover, the effect of AA and its derivatives on 

 metabolic systems in vitro was investigated. 



A first series of experiments showed that AA, when supplied as 



