734 



John D. Spikes and Dennis C. Hall 



processes by 2537 A iiltraviolet radiation and by Cobalt-60 gamma 

 radiation is also presented. 



Considerable v/ork has been done on the differential staining 

 of plant cell organelles with various dyes. Some dyes, such as 

 Rhodamin B^ appear to localize in the chloroplastsw) . Staining 

 Elodea leaves in the light decreased photosynthesis; staining in 

 the dark had no effectv^^^ H) . Similarly^ chloroplasts of cells 

 stained in the light showed a decreased ability to reduce infil- 

 trated silver nitrate(l2). 



Space prevents a detailed discussion of the literature re- 

 lating to effects of ultraviolet and ionizing radiation on photo- 

 synthesis and the Hill reaction. These fields have been recently 

 reviewed; howeverW^^'' . Some work has been done on the compara- 

 tive kinetics of ultraviolet inactivation of the different photo- 

 chemical processes carried out by algae. In Scenedesmus, for 

 example^ photosynthesis, the Hill reaction (as measvired using an 

 indophenol dye), and photoreduction were^all inhibited about 

 equally in a first-order manner by 2537 A ultraviolet 

 radiation(l3) . No comparable comparative studies with ionizing 

 radiation appear to have been published. The photosynthesis of 

 Chlorella as measured by carbon dioxide fixation and oxygen evo- 

 lution can be partially inhibited by gamma irradiation! 1^) . More 

 recently, considerable work has been done on the effects of 

 ionizing radiation on the photochemical properties of isolated 

 chloroplasts (see (7^ 8; 15) for references). 



MATERIALS AND METHODS 



The experiments were carried out with Chlorella pyrenoidosa . 

 Chick, Emerson strain, type D, grown at 25°C. in a modified Knopp 

 medium with continuous agitation while being bubbled with 3^ car- 

 bon dioxide in air. The algae were grown for 72 hours under con- 

 tinuous illumination (800 foot-candles of "white" fluorescent 

 light) and then for Qh hours under alternate 12 hour light and 

 dark periods. Measurements of photosynthesis and Hill reaction 

 were made manoraetrically at 15 °C. using rectangular glass 

 vessels. The vessels were illuminated with 150-watt reflector- 

 flood bxilbs; light intensity v;as approximately iiOOO foot-candles. 

 The Hill reaction system was 0.00^-M in p-benzoquinone, O.O5M in 

 pH 6.8 sodium phosphate buffer, O.OIM in potassium chloride and 

 contained approximately 1^ algae, all in a total volume of 3 rnl. 

 Photosynthesis was measured using Warburg No. 9 buffer. 



