GihbcrelUn-Auxin Interaction and Metabolic Basis 617 



mutants, obtained from Dr. B. O. Phinney, of the University of Cali- 

 fornia at Los Angeles. The genetic differences between the dwarf 

 and tall peas are partially unknown and probably complex, but the 

 dwarf- 1 Zea mutant is known to differ from the wild type by a single 

 gene (17). 



The peas were grown in the light as described above, except that 

 the temperature was maintained at ca. 17° C, rather than 23° C. 

 Fourteen days after planting, half of the plants were treated with 1 

 /xg. GA in 0.003 ml. ethanol, applied to the stipules enclosing the fifth 

 internode. At various intervals after treatment, the plants were har- 

 vested and the fifth internodes excised and homogenized with a pre- 

 chilled mortar and pestle in 0.025 M pH 6.1 phosphate buffer (1 g. 

 fresh wt/10 ml homogenate). The homogenate was then stored in a 

 deep freezer in Lusteroid centrifuge tubes until further use. The 

 peroxidase activity was unchanged by such storage. 



Seven days after planting, the corn was treated with 1 /xg. GA in 

 0.003 ml. ethanol applied to the tip of the first leaf as it emerged from 

 the coleoptile. Two and four days later, the basal third of the first 

 leaf sheath (the rapidly elongating region) of 20 to 30 plants was ex- 

 cised, combined, and homogenized and stored as above. 



Prior to assay, the tissue homogenate was centrifuged at 2,000 X 

 gravity for 10 min. and the clear supernatant made up to standard 

 volume and used for peroxidase and protein nitrogen determinations, 

 according to previously-published procedures (16, 22). The usual sub- 

 strate for peroxidase determinations was pyrogallol, but lAA and 

 guaiacol were also used extensively. Most of the data were obtained 

 with a Klett-Summerson photoelectric colorimeter, but a Spectracord 

 recording spectrophotometer was also employed in later studies, es- 

 pecially with lAA. The results with pyrogallol as substrate are pre- 

 sented in Table 6. It is clear that GA greatly promotes the growth 

 of both dwarfs, while markedly lowering the peroxidase activity per 

 unit protein N. In the dwarf corn, the peroxidase activity of both 

 dwarf and normals rises with increasing age, and the depressive effect 

 of GA appears to result from a prevention of this normal increase. 

 The GA produces much smaller effects on tall corn, and is entirely 

 without effect on tall peas. Thus, based on pyrogallol as a substrate, 

 GA can be said to depress the abnormally high peroxidase activity of 

 dwarf plants. 



When the experiment of Table 6 was repeated with guaiacol as a 

 substrate, then GA was found to increase, rather than decrease, the 

 peroxidase activity of the dwarf tissue. This corroborates a recent re- 

 port (10) on the effect of GA on the peroxidase of rice, in which 

 guaiacol was used as a substrate. These opposite results forced us to 



