Some Effects of 2537 ~ on Green Algae and Chloroplast Preparations*

The experiments recorded in this paper, dealing with effects of 2537/~ on intact ceils of green algae, were initiated in the hope of gaining more insight into the nature and properties of the catalysts of photosynthesis sensitive to 2537/~; and, possibly by comparison of the sensitivities of the various processes studied, to gain some information as to the relation between them. We have investigated: (1) photosynthesis, (2) endogenous respiration, (3) glucose oxidation, (4) photoreduction, (5) oxygen evolution in the presence of a substitute oxidant, i.e. the "Hill reaction," and (6) dark reduction of CO2 coupled to the oxyhydrogen reaction. A similar study of chloroplast preparations was undertaken to compare the effects of 2537 ~ on the Hill reaction in chloroplasts with the effects on the same reaction and on photosynthesis in intact cells; and further, to compare the effects on the Hill reaction with those on other enzymatic systems in chloroplast preparations. For many years it has been known that ultraviolet radiation has a deleterious effect on photosynthesis and cell division. Meier (1-5) found cell multiplication of ChloreUa ~lgaris to exhibit two peaks of sensitivity, one close to 2400/~, and another more pronounced, close to 2600 /~. Stimulating effects on the division of surviving ceils were observed with Stichococcus bacillaris for exposures which killed two-thirds of the cells at the wave lengths 2352, 2483, 2652, and 2967 4. Arnold (6, 7) studied the effects of 2537 ~ on Chlorella pyrenoidosa and found that the rate of photosynthesis is reduced, while that of endogenous respiration is unaffected. A straight line relationship between the logarithm of the rate after irradiation relative to initial rate (log R/Ro) and the duration of exposure was observed, showing that the rate of inactivation was proportional to the capacity for photosynthesis at any given time; i.e., a "first order effect." Identical amounts of inactivation were found when residual photosynthesis was measured in either continuous light or in flashing light with