Occurrence and Role of Growth Hormones 



87 



enzymatic process may dominate in strong light (Bruson and Leopold, 

 impnblished). 



Both the enzymatic and the non-enzymatic auxin-destroying sys- 

 tems have been shown to involve the consumption of oxygen. Evidence 

 concerning the nature of the enzymatic destruction of auxin in peas 

 has indicated that two participants to the enzyme systems are in- 

 volved: a flavo-protein and a peroxidase (Galston and Baker, 1951). 



PIGMENT-H2 



HoO 



2^2 



PIGMENT 



INDOLEAGETIG 

 AGIO 



INDOLEALDEHYDE 

 + GO2 



Fig. 43. A scheme for the photo-destruction of indoleacetic acid (adapted from 



Larsen, 1951). 



Figure 43 represents diagrammatically a concept of the auxin- 

 destroying mechanisms in plants. In this scheme, step 1 involves the 

 oxidation of a reduced pigment or flavo-protein complex. This step 

 utilizes oxygen, and presumably forms peroxide. Step 2 is the en- 

 zymatic step involved in auxin destruction and the evidence indicates 

 that, in peas at least, the enzyme involved may be a peroxidase. By 

 means of this step indoleacetic acid is oxidized to indolealdehyde plus 

 carbon dioxide. An alternative reaction, 2a can occur at this point, a 

 process by which indoleacetic acid is oxidized without the participa- 

 tion of an enzyme. This auto-oxidation is a non-enzymatic destruction 

 of auxin. Still another non-enzymatic destruction of auxin may con- 



