142 



PHOTOCONTROL OF GROWTH 



2nd 3rd 4tti 



Terminol Youngest Youngest Youngest Youngest 

 Bud Intetnode Internod* Internode Internede 



CL < 



C/) 



— 10- 



4 10 I 4 10 ! 4 10 



20 20 



MG. FRESH WEIGHT EQUIVALENT PER 



10 ML REACTION MIXTURE 



Fig. 1. The lAA oxidase activity of various portions of 14-day-old 

 light-grown Alaslca pea seedhngs, measured at various concentrations. 



enzyme activity is lower, but does not fall off so rapidly with increasing 

 concentration. This is probably indicative of a lower level of inhibitor. 

 (3) The leaves showed no activity at all, owing either to low enzymatic 

 activity, high inhibitor level, or both. 



These data were interpreted as meaning in general that lAA oxidase 

 activity is widespread in the stem and young bud tissue of light-grown 

 pea plants, and that there exists, in addition, a gradient in an inhibitor 

 of this enzyme, the inhibitor being most concentrated in the youngest 

 regions of the stem. 



Direct Demonstration of the Inhibitor and Its Gradient in the Plant. 

 The inhibitor of lAA oxidase activity has already been demonstrated 

 to be a water-soluble, heat-stable, low-molecular-weight substance 



