CHLOROPLAST PREPARATIONS FROM DIFFERENT PLANTS 1539 



tannin, which bind Fe(III), was suggested as explanation. (This binding 

 can often be recognized by the formation of highly colored complexes.) 



The five species with which considerable oxygen liberation was observed 

 were Aster tatarica, Mirabilis jalapa, Impatiens hi flora, Tradescaniia fliimi- 

 nensis, and Spinacia oleracea. They all showed rates of the same order of 

 magnitude (related to equal amounts of chlorophyll) ; but considerable 

 variations were found with leaves of each species in dependence on their 

 history. Specifically, the efficiency was found to increase with the dura- 

 tion of preillumination. (In these experiments, detached leaves were kept 

 for 2-3 days in the dark, then illuminated for 2-6 hours before maceration.) 

 The rate of increase in efficiency was only about twice as high in light of 

 50 klux as in 115 klux; in general, the duration of the exposure appeared 

 to be more important than its intensity. If, after 6-hr. illumination, the 

 leaves were again darkened, the activity declined by about 50% in 1.6 

 hrs., and to almost zero in 6 hrs. 



French concluded from these experiments that the Hill reaction is de- 

 pendent on the presence of an accumulated product of photosynthesis 

 which disappears in the dark, and that the maximum efficiency of the Hill 

 reaction can be obtained only by using leaves which had been preillumi- 

 nated for 10 hrs. or more. He suggested that insufficient preillumination 

 might have been responsible for some low quantum yields found by French 

 and Rabideau (Table 29 .X). 



Gurevich (1947) obtained evidence of photochemical reduction of o-dinitrobenzene 

 with chloroplast suspensions from Primula, Stellaria and Atriplex. Andreeva and Zub- 

 kovich (1948), using quinone as oxidant, noted oxygen evolution with chloroplasts from 

 Primula obconica, Spinacia oleracea, Vicia faba, Phaseolus vulgaris, Nicotiana tabacum 

 and Beta vulgaris. They observed no parallelism between the capacities of these species 

 for photosynthesis [5-15 mg. CO2/(100 cm.^ X hr.), at 11 klux] and the efficiency of their 

 chloroplasts in the Hill reaction with quinone [40-250 mm.' 02/(mg. chlorophyll X hr.) 

 in light of the same intensity]. Older leaves of Beta vulgaris were more effective in the 

 quinone reaction than the younger ones ; leaves gathered in good weather were more ef- 

 fective than those collected in rain or cloudy weather. Preillumination of leaves col- 

 lected in dim light with a 1000-watt lamp for 3 hrs. was found to unprove their efficiency, 

 in agreement with the observations of Kumm and French. 



Holt et al. (1951) found poke weed, Phytolacca americana, a particularly 

 convenient source for the preparation of chlorophyll. 



The most extensive comparative study of photochemical efficiency of 

 chloroplasts from different plants was made by Clendenning and Gorham 

 (1950^). They measured the rate of liberation of oxygen in the first 5 

 min. of illumination with Hill's mixture as oxidant, using pH change 

 (cf. under (/) below) as the rate of reaction measure. Tests were made 

 with crude chloroplast preparations (obtained by grinding leaves and re- 

 moving large debris by centrifuging at 2300 g.) from 80 species of uni- 



