lAA OXIDASE INHIBITOR AND MORPHOGENESIS 



149 



(Brian and Hemming, 1955) and for maize (Phinney, 1956) that 

 dbberellic acid (GA) so enhances the growth of certain dwarf races 

 as practically to eliminate the growth differences between tall and 

 dwarf forms. If, therefore, the differences in inhibitor content between 

 tall and dwarf peas shown above are physiologically meaningful, one 

 should expect pretreatment with gibbereilic acid to raise the inhibitor 

 level of the leaflets. This result was actually obtained in many experi- 

 ments, although occasionally, and without apparent reason, GA appli- 

 cations to the plants had no effect on leaflet inhibitor content. 



GA was applied to the tissues in one of several ways, (a) Solutions 

 of GA in dilute buffer were placed in large plastic tubs, and the perfor- 

 ated polyethylene containers holding several plants were immersed in 

 the solution to a depth of ca. 3 cm. Uptake of GA was thus exclusively 

 through the root system, (b) Stems were severed at the ground level 

 and placed with their cut ends in GA solutions, (c) Individual leaflets 

 of the youngest expanded leaves were excised and floated on GA 

 solutions, (d) Discs of leaflets or cylinders of stem were removed with 



GA (M) 



Fig. 4. The effect of various concentrations of gibbereilic acid adminis- 

 tered via the roots to intact plants on the lAA oxidase inhibitor content 

 of youngest expanded leaflets. GA applied 40 hr prior to harvest. 



