412 



N. M. SISAKYAN 



found in the first fraction (3000 > g) indicates that the structures possessing the 

 cyclophorasc activit}' begin to come down at rather lower rates of centrifugation 

 than 3000 g. Activity' is absent from the fraction containing the smallest particles, 

 which comes down in the range 8500-16,500 g. Microscopic checking showed 

 that the fractions which had been studied were composed of structures of two 

 types, complete and pardy disrupted chloroplasts and particles of a perfectiy 

 circular shape many times smaller than whole chloroplasts. The first fraction 

 which comes down at 3000 X g consists mainly of chloroplasts and fragments 

 of chloroplasts with a small admixture in the form of finer structures. The 

 reverse quantitative relationship obtains in the second and more active fraction 

 which comes down at 8500 y. g. This fraction contains mainly fine structures 

 with a small admixture of chloroplasts and pieces of chloroplasts. The third 

 fraction contains a small quantity, which is probably to be regarded as due to 

 contamination, of the structures which come down in the second fraction. There 

 are no other visible structiues in this fraction. 



150 



Fig. 3. Cyclophorasc activity in fractions of intracellular structures from the 



shoots of peas. I — Green plants grown under indoor illumination; II — Etiolated 



plants; III — Green plants grown at low temperatures. 



Dotted curves represent fractions brought down at 3000 g; solid curves those 

 brought down at 8000 g. 



From these facts it is quite clear that the different character of the cyclophorase 

 activity in the different fractions is associated with a non-uniform distribution 

 of structures. 



It has further been estabhshed (cf. curves II in Fig. 3) that the character of 

 the distribution of cyclophorase activity is just the same in etiolated and green 

 plants. It seems that structures isolated from plants which have been grown in 

 summer under conditions of natural illumination at temperattires of 20-25°C 

 either do not have any cyclophorase activity or have it only to a very slight extent. 

 Thus, cyclophorase activity depends, not only on structural organization, but 

 also on the intensity of illumination and the temperature conditions under which 

 the structures were formed. At comparatively high temperatures (20-25'' C) 

 activity of the cycle is only to be found under conditions of inadequate illumina- 

 tion, e.g. in completely etiolated plants and in plants grown indoors. The ratio 



