lAA OXIDASE INHIBITOR AND MORPHOGENESIS 145 



Table II and revealed in addition the fact that the smaller the 

 terminal bud, the higher its inhibitor concentration. Thus, terminal 

 buds less than 7 mm in length had higher lAA oxidase activities per 

 unit protein (at low brei concentrations) than 8-, 10-, 12-, or 14-mm 

 buds, in that order. With increasing brei concentration, the order of 

 activity changed. Direct inhibitor assays revealed that the youngest 

 buds actually had the highest inhibitor content. Thus, the generaliza- 

 tion holds that youngest tissues are richest in inhibitor. 



Effect of Light-Dark Alterations on Inhibitor Content and Oxidase 

 A ctivity. Tang and Bonner ( 1 947 ) showed that exposure of etiolated 

 pea seedlings to light resulted in a fall in lAA oxidase activity and an 

 increase in'the content of inhibitor. Both of these effects were linearly 

 proportional to the daily duration of illumination. We were able to 

 show the same kind of response to light duration in green peas. 



Seedlings were grown under daily photoperiods of 8, 16, or 24 hr 

 for 2 weeks. The youngest internodes were then harvested, and 500 

 mg made up into 50 ml of brei, as usual. One-half milliliter of brei was 

 then added per 10 ml of reaction mixture, and the lAA oxidase activity 

 was measured. Concurrently, the inhibitor content of the youngest 

 leaflet from the same plants was measured, inhibitor being extracted by 

 direct boiling of intact tissue and being added to the enzyme obtained 

 from completely etiolated plants, as before. The results, shown in 

 Table III, demonstrate a simultaneous rise in inhibitor and decline in 



Table III. Effect of Daily Duration of Illumination on Inhibitor Content and lAA 



Oxidase Activity of Green Alaska Pea Seedlings (All seedlings 14 days old, grown 



under ca. 1500 ft-c of fluorescent light; initial Salkowski color = 270) 



lAA Oxidase Activity of 

 Inhibitor-Free Enzyme, 

 lAA Oxidase Activity of Appropriate Inhibitor 



Stem, Extract Added, 



Daily Photoperiod, hr A Salkowski Color/60 min A Salkowski Color/60 min 



— (control, no inhibitor) — 194 



8 174 185 



16 135 151 



24 17 



enzymatic activity with increasing photoperiod. Although the close 

 coincidence of the numbers in the two data columns is probably at least 

 partly fortuitous, the simultaneous and approximately equal movement 



