140 PHOTOCONTROL OF GROWTH 



lite vermiculite in perforated rectangular polyethylene containers. The 

 containers were placed on stainless steel growth tables, equipped with 

 automatic subirrigation units. These tables, constructed to our specifi- 

 cations by the A. B. Stanley Company, Chestnut Hill, Massachusetts, 

 have afforded automatic and virtually trouble-free growth of plants for 

 over a year. 



The nutrient solution for each table consisted of 120 g of Hyponex 

 (Hydroponic Chemical Company, Copley, Ohio) per 100 liters of tap 

 water, changed every 2 weeks. The nutrient solution is circulated to 

 the upper level by a marine type motor, equipped with a stainless steel 

 rotor and Teflon bearings. The motor is set into operation by a time 

 clock, fixed to operate daily for two 15-min periods, at intervals of 12 

 hr. During this 15-min cycle there are approximately three return 

 flushes of the nutrient solution to the tank. Under these conditions, 

 growth of the plants was uniform and rapid. 



The growth tables were placed in air-conditioned rooms maintained 

 at various temperatures and photoperiods. For the bulk of these ex- 

 periments plants were grown under continuous illumination at 17°C. 

 The light was provided by banks of closely packed slimline fluorescent 

 tubes, consisting of alternate cool-white and warm-white tubes. No 

 incandescent illumination was supplied. The light intensity at the 

 surface of the plant was about 2000 ft-c. 



Plants were usually harvested at the age of 14 days and separated 

 into the various portions assayed. For lAA oxidase assays the tissues 

 were converted to a brei by grinding in O.IM phosphate buffer (pH 

 6.1) in a mortar previously stored in a deep freeze. The tissue was 

 frozen to a slurry by contact with the mortar and was kept cold 

 throughout the operation. Subsequent to grinding, the brei was centri- 

 fuged briefly (10 min, 2000 X ^) to remove cell-wall debris, and the 

 supernatant liquid was made up to volume. 



For assay of inhibitor, it was essential to obtain an inhibitor-free 

 enzyme preparation of high activity. This was done by grinding third 

 internode tissue of etiolated 7-day-old Alaska peas in the same manner 

 as described above, 100 mg fr. wt. tissue being present per milHliter 

 of final enzyme solution. 



The inhibitor was prepared from green tissue in three ways, all of 

 which yielded approximately the same results, (a) Brei was dialyzed 



