78 



MINERAL SALTS ABSORPTION IN PLANTS 



5 10 15 20 25 30 35 40 45 



COg evolved, /^equiv.xlO 



Salt 

 odded 



Cyanide 

 added 



"O 



o 



c 



>< 



(b) 



'Ground' respirotion 



_L 



1 2 3 4 5 



Time, hr 



Fig. 28 (a-b). The Lundegardh hypothesis 



a. Relationship between anion uptake and respiration in wheat roots placed 

 in solutions containing various concentrations of potassium nitrate (O) and 

 potassium chloride (El) (redrawn from Lundegardh and Burstrom, 1933); 



b. Effects of salt and cyanide on oxygen absorption by disks of storage tissue 

 (based on data of Robertson and Turner, 1945). 



oxidase and further to suggest that cytochrome may be the carrier 

 for anions. Additional support for these ideas was provided by the 

 observation that absorption and salt respiration are inhibited by a 

 more specific inhibitor of cytochrome oxidase than cyanide, namely 

 carbon monoxide in the dark. Some details of the mechanism 

 proposed by Lundegardh as it is now conceived are shown in Fig. 

 28c. It is postulated that an oxidation-reduction potential gradient 

 exists across the functional membrane, such that cytochrome 

 molecules tend to become oxidized at the outer surface, and reduced 



