1550 



PHOTOCHEMISTRY OF CHLOROPHYLL 



CHAP. 35 



lar, if slightly weaker, effect; iodide and nitrate had a small effect, while 

 fluoride, rhodanide, sulfate and phosphate were without influence. 



Arnon and Whatley (1949^) noted that the importance of chloride de- 

 pended on the nature of the oxidant used. For example, the total oxygen 

 yield obtainable from a certain quantity of quinone was reduced from 100% 

 of the stoichiometric equivalent in the presence of 0.01 M KCl, to 36% 

 without KCl; with ferricyanide, the reduction was from 100 to 19%; but 



100 



KNO. 



^0 a NaF 



„^ o — Q — o — * 



,§--9::r:2 — •— * — • • control 



6 10 14 



TIME, minutes 



18 22 



Fig. 35.11. Activation of Hill reaction in chloroplast preparations from chloride- 

 free cells by salts (after Arnon and Whatley 1949'^). 



with phenol indophenol, the change was only from 100 to 90%. However, 

 chloride proved equally important for obtaining a high initial rate of the 

 reduction of all three oxidants. 



Arnon and Whatley (19492) pointed out that CI" is not a necessary 

 plant nutrient; it is therefore unlikely that it is a natural component of 

 the photosynthetic apparatus (as suggested by Warburg and Liittgens). 

 They grew sugar beet and Swiss chard in chloride-free nutrient solutions. 



