82 



MINERAL SALTS ABSORPTION IN PLANTS 



c 

 o 



0- 

 Q 



electron transport in barley roots and could conceivably function as 

 an ion carrier in a basically similar manner to cytochrome. In 

 anaerobic organisms, electron transport and anion absorption must 

 obviously be linked to other systems than that involving cyto- 

 chromes and oxygen. 



(c) It is by no means certain that the stimulation of respiration 

 caused by salt is due more to the presence of anions than of cations. 

 Hoagland and Steward (1939) pointed out that the ions having 

 greatest effects on respiration in their experiments were those 



In HjO 



100 





(U 

 Q. 



O 



E 

 E 

 o 



iOO 



50 



In 0-05 M KCL 

 (b) 



T3 

 O 



E 



3 





J L 



10 20 30 40 



10 20 30 40 



Concn.of 2-4 dinitrophenol , mg/L 



Fig. 30. Salt absorption and respiration. Relationship between concentra- 

 tion of dinitrophenol (DNP) and a-b, the rate of DNP respiration (i.e. the 

 rate of O2 absorption in DNP over that in water or salt), and c, the amount of 

 KCl accumulated in carrot tissue; X, O, and A— disks from one batch 

 of carrots, respectively 144, 264 and 312 hr after cutting: □ from another 

 batch of carrots, 96 hr from cutting (redrawn from Robertson, Wilkins and 



Weeks, 1951). 



containing nitrogen, i.e. an anion (NO7) and a cation (NH4). 

 Epstein (1954) demonstrated that salt respiration is stimulated in 

 the presence of a cation exchange resin from which anions are not 

 absorbed. 



(d) The Lundegardh hypothesis rests on the establishment of a 

 quantitative relationship between cyanide-sensitive respiration and 

 anion uptake. Some discrepancies between the two processes were 

 noted by Lundegardh (1940), but not emphasised unduly. Strong 

 evidence against the hypothesis was supplied by the observation of 

 Robertson et al. (1951) that 2:4 dinitrophenol (DNP), at certain 



