304 



CATALYST POISONS AND NARCOTICS 



CHAP. 12 



''general vitality" of the protoplasm — hence its uniform influence on 

 respiration and photosynthesis, whereas, in Chlorella, it acts directly 

 and independently on each of these two processes. That the behavior 

 of two closely related species should be so different seems implausible; 

 we shall see below that a simpler explanation can be suggested. 



In a subsequent investigation (1935), van der Paauw used Stichococcus 

 hacillaris, an alga which is resistant to alkaline buffer solutions and could 

 therefore be studied in Warburg's manometric apparatus, instead of in 

 van der Honert's gas flow apparatus (cf. Vol. II, Chapter 25) which had 

 to be used for work on Hormidium. The results were described by van 

 der Paauw as "intermediate between those obtained with Chlorella and 

 Hormidium.'^ On the one hand, Stichococcus, similarly to Hormidium, 

 showed a stimulation of photosynthesis by small quantities of cyanide 

 (up to 10-^ m./l.), and inhibition only above 10"^ m./l. HCN. On the 

 other hand, the photosynthesis of Stichococcus, similarly to that of 

 Chlorella, could not be reduced by cyanide below the compensation point. 

 The ratio of the "residual photosynthesis" of poisoned algae to that of 

 the nonpoisoned ones is expressed by P/Po in table 12.IV. Respiration 



Table 12.IV 

 Effect of HCN on Photosynthesis of Stichococcus (after van der Paauw) 



in Stichococcus is doubled by cyanide stimulation, without a sign of 

 incipient inhibition even at 0.02 m./l. HCN; the resistance of its respira- 

 tory system to cyanide is thus even stronger than that of Chlorella. 



Emerson (1929) has investigated the effect of cyanide on Chlorella 

 pyrenoidosa with an artificially reduced chlorophyll content. A concen- 

 tration of 9 X 10~^ m./l. HCN reduced the rate of photosynthesis by 

 40% in cells with a chlorophyll content of 0.037 relative units, by 30% 

 in cells with [Chi] = 0.060, and by 25% in cells with [Chi] = 0.083. 

 Thus, Chlorella cells poor in chlorophyll were more sensitive to cyanide 

 than those with a normal chlorophyll content. This was interpreted by 

 Emerson as an indication that a reduction in chlorophyll concentration 

 reduces the capacity of Chlorella for an enzymatic reaction. Together 

 with other observations (e. g., those on the temperature coefficient of 

 photosynthesis in chlorophyll-deficient cells; cf. Vol. II, Chapter 31) 

 these results have been taken by Emerson as indicating the participation 

 of chlorophyll in a nonphotochemical, catalytic reaction in photosynthesis. 



