IONIC INHIBITION EFFECTS 



341 



same region (osmotic pressure of about 15 atm.) in which photosynthesis 

 was inhibited by sucrose (c/. page 334 and Fig. 34, Curve 6). Zinc 

 sulfate and nickel sulfate produced inhibition at concentrations of the 

 order of 0.1 m./l., that is, somewhat before it should occur if it were 

 purely osmotic in origin (Fig. 34, Curve 2). Zinc sulfate and nickel 



lOO 



80 



» 



r60 



J40 



20 



10" 



10" 



10" 



10" 



Concentration 



A 



10" 



0.01 o.oas 0.05 0.1 0.2 



Concantratton 



B 



04 0.6 1.0 



0.2 0.3 0.4 0.5 06 0.8 1.0 



Concentration 



100 



80 



£ 60 



c 

 >. 



o 



o 40 



a 



20 

 



0.2 0.3 0.4 0.6 0.8 1.0 



Concentration 



D 



Fig. 34.— Inhibition of photosynthesis of Chlorella by different ions and by sucrose 

 (22,000 lux) (after Greenfield 1942). A, specific poisons; B, weak inhibitors; C and D, 

 osmotic effects. (C, indifferent salts; D, sucrose in buffer.) 



sulfate inhibited the dark reaction only; whereas cupric and cobaltous 

 sulfates reduced the oxygen production in strong, as well as in weak, 

 light (c/. Fig. 35). 



(d) Anions 



Greenfield (1941, 1942) observed the inhibiting effect of iodides and 

 borates on the photosynthesis of Chlorella; it occurred only in strong 

 light. He also noticed that 0.1 m./l. potassium chloride inhibits photo- 



