1062 THE LIGHT FACTOR. I. INTENSITY CHAP. 28 



and by 6% when it was 4.7 kerg/cm.- sec, but left it unchanged at 70 

 kerg/cm.2 sec. In other words, the effect of cyanide was in this case simi- 

 lar to that of low temperature (or carbon dioxide deficiency); all three 

 caused a shift of the critical intensity, /„ toward lower light intensities, 

 but did not affect the two "hmiting" yields, (pi and (p2. Working with dia- 

 toms, Wassink and Kersten (1945) found the cyanide effect similar to that 

 of lowering of temperature (fig. 28.33) and of addition (not removal!) of 

 carbon dioxide. Up to about 6 kerg/cm.^ sec, the yield of fluorescence (at 

 25° C.) was slightly increased by 0.003% KCN but, above this intensity, 

 the yield became much smaller in the presence of the poison (fig. 28.44). 

 Here again, we note the contradiction to other observations in the apparent 

 similarity between the curve obtained with carbon dioxide and that ob- 

 served with hydrogen cyanide (usually addition of hydrogen cj^anide has 

 been found to produce the same effect as deprivation of carbon dioxide). 

 Furthermore, one notes that in figure 28.44 the noninhibited sample showed 

 a marked increase in <p at high light intensities in contradiction to the per- 

 fectly straight line given for similar conditions in figure 28.39). 



At 6° C, the yield, (p, remained constant in the presence of cyanide, 

 up to 130 kerg; it looked as if in this case the low yield, (p2, prevailed down 

 to the lowest light intensities used. 



Katz, Wassink and Dorrestein (1941) stated that in purple bacteria, as in 

 Chlorella, the effect of cyanide on the transition intensity, 7^, is similar to 

 that of a decrease in the concentration of carbon dioxide. Wassink, Katz 

 and Dorrestein (1942) gave several fluorescence curves for potassium cy- 

 anide-poisoned bacteria. In the absence of reductants, the addition of up 

 to 0.0167% KCN had no effect on fluorescence — a result analogous to that 

 obtained in carbon dioxide starvation experiments, and thus in agreement 

 with the assumption that hydrogen cyanide is primarily a poison for carbon 

 dioxide fixation. Very high cyanide concentration, on the other hand, had 

 a strong depressing effect on fluorescence of Chromatiiim, even in the ab- 

 sence of hydrogen donors (>50% depression in 0.05% KCN). In the 

 presence of reductants, fluorescence curves with and without cyanide 

 (figs. 28.45) showed small but distinct differences, again somewhat similar 

 to those found with varying carbon dioxide supply (cf. fig. 28.30). 



(e) Hydroxylamine and Azide 



Observations of the effect of these two poisons on fluorescence were 

 made by Wassink and co-workers (1942) in purple bacteria. They are 

 illustrated by figs. 28.46-28.47 (p. 1064). The influence of hydroxylamine 

 appears similar to that of potassium cyanide — no effect up to 0.05% (a 

 concentration at which photosynthesis is about 50% inhibited), then (at 



