lAA OXIDASE INHIBITOR AND MORPHOGENESIS 153 



inhibitory substances. Work to date has indicated that conditions must 

 be controlled very carefully in order to obtain consistent results. It has 

 been observed that the Rfs obtained on Whatman :#:! paper and those 

 on 4^3 paper are not comparable. Future runs will be made along with 

 certain arbitrary standard substances to facilitate comparisons. 



Location of the inhibitor on chromatograms is frequently difficult 

 unless very large amounts of material are applied to the paper. Seldom 

 is a well-defined area containing inhibitory activity obtained, but the 

 activity can be recovered if large areas of the paper are eluted and 

 tested together. This, in addition to the evidence from the column 

 fractionation has suggested the presence of a multiplicity of com- 

 pounds with inhibitory activity, each present in quite small amount. 



STUDIES ON A COFACTOR FOR lAA OXIDASE 



Various workers (Kenten, 1955; Waygood ^r a/., 1956) have found 

 that extracts of various plant parts contain substances, presumably 

 phenolic in nature, which enhance the activity of lAA oxidase prepara- 

 tions. Such a material is also present in the terminal buds of com- 

 pletely etiolated peas, but it is absent from green material. The condi- 

 tions of its occurrence are thus exactly the opposite of the inhibitor, 

 and, in fact, certain experiments have suggested that the cofactor is 

 transformed, by photomorphogenically active light, into the inhibitor. 

 We have therefore been conducting a parallel investigation into the 

 chemical nature of the extractable cofactor. 



The cofactor is best prepared by dialysis of a brei of etiolated pea 

 buds. It is either completely absent from or present in small quantities 

 in stem tissue. In combination with MnCb (10~^M), but in the ab- 

 sence of 2,4-dichlorophenol, the cofactor enhances the oxidation of 

 lAA by the etiolated pea lAA oxidase system (Fig. 5). Once again, 

 although we depend on this system for assay, we do not necessarily 

 imply that the biological action of the cofactor is involved with lAA 

 destruction. 



The cofactor is insoluble in ether, unstable to base, especially at 

 elevated temperatures, and can also be destroyed by 12-min boiling in 

 O.IA^ acid or by ashing. It is readily adsorbed onto Dowex-1 resin, but 

 not easily eluted. Chromatographic resolution on cellulose powder 



