146 P. L. Goldacre 



that inhibition occurs in the absence of natural cofactor or added 

 phenolic carrier due to the catalytic diversion of peroxide: 



M„0 ^ MnOa 



MnOo + H.O, > MnO + O. + H,.0 



MnO + MnO. > MuoOg 



Mn.O;, + H.O, > 2MnO + Oo + H.O 



Promotion occurs in the presence of natural cofactor or DCP by fa- 

 cilitating utilization of peroxide (13, 20). 



Thus, it seems that purified peroxidase can mediate the peroxi- 

 dation of lAA and the oxidation (by oxygen) of its product. This is 

 not an unique instance, highly purified peroxidases acting similarly 

 toward dihydroxymaleic acid (16), tryptophan (15), phenylacetalde- 

 hyde (12), and certain dicarboxylic acids (14) . 



It is now established (11, 18) that plant tissues contain several sep- 

 arable peroxidases, differing in substrate specificities. It would be 

 desirable to compare the peroxidase components of tissues under 

 study, determine wliich can mediate lAA oxidation, and examine 

 whether these separated components show any differential response 

 to light or DCP. 



The total lAA oxidase activity of pea epicotyl brei may be con- 

 tributed to by a number of enzymatic components, and modified by 

 the presence of manganese, natural cofactors and inhibitors, and 

 light. The important task facing us is not only to resolve the descrip- 

 tive biochemistry of the macerates, especially for each tissue under 

 consideration, but to interpret the meaning of this lAA-destroying 

 activity for the plant. 



LITERATURE CITED 



1. Uoiincr, \V. D., Jr. Soluble oxidases and their functions. Ann. Rc\ . IMant 

 I'hysiol. 8: 427-452. 1957. 



2. Briggs, \V. R., Sleeves, T. A., Sussex, I. M., and Wetmore, R. H. .\ compari- 

 son of auxin destruction by tissue extracts and intact tissues of the fern Os- 

 munda cinnamomca L. Plant Physiol. 30: 148-155. 1955. 



3. Galston, A. W., and Baker, R. S. Studies on the physiology of light action. II. 

 The phoiodynamic action of riboflavin. Amcr. jour. Rot. 36: 773-71^0. 1949. 



4. , and Baker, R. S. Studies on the physiology of light action. III. light 



activation of a flavoprotein enzyme by reversal of a naturally occurring inliibi- 

 tion. Amer. Jour. Bot. 38: 190-195. I95I. 



5. , Bonner, J., and Baker, R. S. Flavoprotein and peroxidase as com- 

 ponents of the indoleacetic acid oxidase system of jJcas. Arch. Biochem. Bio- 

 phys. 42: 456-470. 1953. 



6. Goldacre, P. L. Hydrogen peroxidase in the enzymatic oxidation of hctcro- 

 auxin. Austral. Jour. Sci. Res. Ser. B. 4: 293-302. 1951. 



