144 



PHOTOCONTROL OF GROWTH 



Table II. Relative Inhibitor Content of Dialyzates of Breis Prepared from Vari- 

 ous Portions of 2-Week-Old Light-Grown Alaska Pea Plants (50 ml brei (= 500 mg 

 fr. wt. tissue) dialyzed overnight at 2°C vs 50 ml O.IM pH 6.1 phosphate buffer; 

 1 ml dialyzate then added per the usual 10 ml of reaction mixture; initial Salkowski 



color (time 0) = 270) 



Tissue Used 

 None (control) 



Stem, youngest internode 

 Stem, all other internodes 



Leaflets and stipules, youngest leaf 

 Leaflets and stipules, leaf 2 

 Leaflets and stipules, leaf 3 



Petioles and tendrils, youngest leaf 

 Petioles and tendrils, leaf 2 

 Petioles and tendrils, leaf 3 



The following facts are clearly demonstrated by the data of Table 

 II. ( 1 ) The inhibitor is most abundant in young tissues of all kinds, 

 decreasing in concentration in progressively older tissues. (2) It is 

 most concentrated in the youngest internode of the stem, next most 

 abundant in the laminar tissues of the youngest expanded leaf, least 

 abundant in the petioles and tendrils. 



Since the inhibitor is heat stable (Tang and Bonner, 1947) and 

 since preparation of the inhibitor by dialysis requires at least 16 hr, it 

 was reasoned that the inhibitor could be collected quantitatively more 

 conveniently by simple boiling of either brei or intact tissue. It was 

 found that complete recovery of inhibitor results from exposure of brei 

 to 100°C in a boiling water bath for 5-10 min, followed by filtration 

 to remove coagulated proteins. Approximately the same recovery can 

 be obtained by boiling the intact tissue in distilled water. Under these 

 conditions, the content of inhibitor in the water rises for about 20 

 min, then falls off slowly with time. This probably means that more 

 and more inhibitor is extracted with increased boiling time, but that 

 some thermal destruction occurs on prolonged boiling. 



Further inhibitor assays were made, by using the technique of boil- 

 ing intact tissues for inhibitor extraction (10 mg fr. wt. ml Hl-O). Re- 

 sults of such assays confirmed the distribution of inhibitor shown in 



