1546 



PHOTOCHEMISTRY OF CHLOROPHYLL 



CHAP. 35 



be stored at 5° C. (or lower temperature) without further loss of activity. 

 It was noted that while snap freezing of fresh material at very low tempera- 

 ture ( — 75° C.) did not damage it, preparations which were first stored at 

 -40° C. for a while lost some of their activity if they were cooled down to 

 — 75° C. before thawing. Figure 35.8A shows the loss of photochemical 

 activity, at 10° C, of fresh and of snap frozen chloroplasts ; propylene 

 glycol is shown to slow down the deterioration in the first 1-2 hours after 

 thawing. 



Vereshchinsky (1951) described preservation of chloroplasts by snap 

 freezing of a suspension in phosphate buffer (pH 6.5) at —183° C. Sus- 

 pension drops were allowed to fall into liquid air (not liquid nitrogen, to 

 avoid submerging). 



Table 35. VII summarizes various observations on the deterioration of 

 chloroplast preparations. 



Table 35.VII 

 Deterioration of Chloroplast Preparations 



" Extrapolation indicates 25% loss during preparation. 



Milner, French et al. (1950) found no difference in stability between 

 chloroplast preparations stored in air or in oxygen-free atmosphere- 

 indicating that deactivation was not the result of autoxidation. Phosphate 

 buffering (pR 6.5) merely made the decay faster; however, Warburg and 

 Luttgens (1946) and Arnon and Whatley (1949) reported a faster deteriora- 

 tion in water, as compared to phosphate buffer. Holt, Smith and French 

 (1951) found that in 0.02 M sodium sorbitol borate buffers of different pH, 

 the photochemical activity of spinach chloroplasts (measured colorimetri- 



