PREPARATION, PRESERVATION AND ACTIVATION OF CHLOROPLASTS 1547 



cally with phenol indophenol) was best preserved at pH 6.5 ( >90% activity 

 preserved after 2 hrs. at 0° C, about 25% after 10 min. at 35° C.) . At pH 

 5.0 or 7.5 the losses were greater (>35% after 2 hrs. at 0° C. and >80% 

 after 10 min. at35° C). 



Kiimm and French (1946) found that when leaves were preilluminated 

 for several hours before maceration they not only showed a higher photo- 

 chemical efficiency (as described in section 2 above), but also kept better in 

 storage. However, Clendenning and Gorham (1950^) noticed no such sta- 

 bihzing effect in experiments with chloroplasts from Swiss chard. 



100 



> 



o 



< 



Fig. 35.9. Stabilization of chloroplast activity by methanol (after 

 Milner, French, Koenig and Lawrence 1950). 



Zubkovich and Andreeva (1949) looked for any parallelism between 

 the decay of photochemical activity and changes in the absorption spectrum 

 of chloroplasts, their fluorescence, the concentration of chlorophyll, and its 

 association with proteins. As the activity of sugar beet chloroplasts de- 

 creased with time (e. g., from 43 mm.* O2 per hour per milhliter of suspension 

 to 9 mm.3 after 2 days at 2-3° C; or to 6 mm.* after 2 hours at 30° C), 

 the total chlorophyll content was found unchanged (0.49 mg. per cm.*); 

 but the part of it extractable by 60% acetone (which is a measure of the 

 chlorophyll attachment to protein), declined from 37% to 25 and 29%, 

 respectively. The shape of the red absorption band was unchanged, and 

 the suspension still fluoresced. With material from Phaseolus vulgaris, 

 no change was noted also in the percentage of chlorophyll extractable with 

 aqueous acetone, even after the photochemical activity had dropped, after 



