CHLOROPLAST PREPARATIONS FROM DIFFERENT PLANTS 1541 



chemical activity of the chloroplast preparations (related to unit chloro- 

 phyll weight) to decline by as much as 50%. Incipient wilting of wheat 

 leaves increased the chloroplast activity by up to 40% ; progressive wilt- 

 ing depressed it. 



Leaves (of wheat or spinach) collected at various times of the day did 

 not show the wide variations in activity previously described by Hill and 

 Scarisbrick (1940) for chloroplasts from Stellaria media; checks with the 

 latter plant also showed no strong variations. 



Keeping leaves of New Zealand spinach in the dark for 48 hrs. did not 

 affect significantly the activity of their chloroplasts — contrary to the ob- 

 servations of Kumm and French with Tradescantia; with the latter plant, 

 too, Clendenning and Gorham could obtain no confirmation of Kumm 

 and French's observations. Spinach showed complete loss of activity (with 

 Hill solutions as oxidant) after only 6 hrs. in darkness; with quinone as 

 oxidant the activity declined to 34 of the original one after 4 days in dark- 

 ness, but remained constant afterwards. No marked recovery followed 

 upon renewed illumination for 6 hrs. These experiments do not support 

 the hypothesis of Kumm and French that the Hill reaction involves a 

 photosynthetic product, which slowly accumulates in light and disappears 

 in darkness. 



Punnett and Fabiyi (1953) and Hill, Northcote and Davenport (1953) 

 described methods for the preparation of photochemically active chloro- 

 plast preparations from unicellular algae. Punnett and Fabiyi stirred the 

 cells with alumina powder into a paste and squeezed it through a fine open- 

 ing in a steel cylinder under high pressure, took up the product in 0.03 M 

 phosphate buffer (pH 6.7) containing 0.3 M sucrose, and threw alumina 

 and whole cells down by centrifugation. The suspensions of the chloroplast 

 fragments obtained in this way produced oxygen in light, with ferricyanide 

 as oxidant, at the same rate as chloroplast preparations from Phytolacca 

 americana; the rate remained constant for at least 15 min. Such active 

 suspensions were made successfully from Chlorella (pyrenoidosa or vulgaris) 

 and Bractcococcus, but not from Scencdcsmus obliquus, which did not break 

 in the pressure cylinder. The blue-green Anahaena variabilis disintegrated 

 easily, but neither the crude macerate (containing phycocyanin in solution) 

 nor the precipitated and resuspended fragments gave Hill reaction in light. 



Hill and co-workers (1953) obtained similar algal chloroplast prepara- 

 tions with the Mickle cell disintegrator. They noted that the green juice 

 which remained after the precipitation of cell walls from disintegrated 

 Chlorella had the capacity for indirect photochemical reduction of methe- 

 moglobin, indicative of the presence of an intermediate hydrogen acceptor 

 first discovered in leaves {cf. below, section 4(/)). The same cytochromes 

 Hill et al. had found in leaf plastids {cf. chapter 37A) appeared also in 

 Chlorella chloroplasts. 



