PREPARATION, PRESERVATION AND ACTIVATION OF CHLOROPLASTS 1545 



(1950^) reported that snap-freezing in dry ice in the presence of a molar 

 sucrose solution and rapid thawing at room temperature led to preserva- 

 tion of the activity both in crude leaf macerates and in separated chloro- 

 plast suspensions. The chloroplasts treated in this way showed no decline 

 in activity after storage at —40° C. for 14 days; but at — 12° C. only 10% 

 of the original activity was preserved after the same period. According 

 to French and Milner (1951), lyophylized material resists attempts to dis- 

 perse it into fine particles and is therefore luisuitable for the preparation of 

 colloidal chloroplast dispersions. 



1400 



1200 



1000 



800 



-c^ 



600 



400 



200 



VTHAWEO 



UNFROZ 



PROPYLENE GLYCOL, 

 THAWED 



STORAGE TIME. HOURS 



Fig. 35.8A. Deterioration of chloroplast material at 10° C. (Gorham and 

 Clendenning 1950). 0.5 mg. Chi per vessel. (•) Fresh crude suspension in 0.5 

 M sucrose; (O) crude suspension, frozen and thawed, in 0.5 M sucrose; (□) same 

 + 10% propylene glycol. 



Gorham and Clendenning (1950) reported that chloroplasts stored for 

 one year in 0.5 M sucrose at —40° C. showed, upon thawing, the same ac- 

 tivity (within 5%) as fresh preparations. Washed chloroplasts were pre- 

 served less well than nonwashed ones. Preservation was equally good with 

 material from spinach, millet, flax, Smss chard and other species; it was 

 tested with Hill's mixture, ferricyanide, quinone and chromate. Preserva- 

 tion by vacuum drying ("lyophylizing") was less effective. Deterioration 

 occurred mainly in the early stages of drying; once dry, the material could 



