64 



MINERAL SALTS ABSORPTION IN PLANTS 



a. 



7-0 



6-0 



5-0 



4-0 



300r 



tI4 



20 40 



Time, min 



1+10 



o 

 CO 



[|.A.a], mg/l 



Fig. 2L Effects of glucose [a] and auxin [b] on salt absoprtion 



a. Changes with time in the potassium content (— ), pH ( ) and glucose 



( ) content of the medium in which Escherichia coli cells were suspended 



(redrawn from Leibovitz and Kupermintz, 1942); b. Amounts of salt 



absorbed (□) and the change in fresh wt. (O) of potato slices placed in 



solutions containing salt and various concentrations of indole (3) acetic 



acid in 48 hr (redrawn from Commoner and Mazia, 1942). 



Stances which are essential for growth, for example vitamins and 

 auxins, to the medium stimulates salt uptake if growth is limited 

 by these factors (Fig, 21b). 



Metabolic inhibitors reduce or entirely suppress active salt 

 absorption over approximately the same range of concentration as 

 they inhibit respiration, but absorption of salt is often inhibited 

 completely at levels wliich do not entirely prevent oxygen uptake 

 (Machlis, 1944). 2:4 dinitrophenol and other uncouphng agents 

 depress salt uptake at certain concentrations but stimulate oxygen 

 absorption (see Fig. 30, p. 82). Inhibitors of protein synthesis (e.g. 

 ribonuclease, 8-azaguanine and chloramphenicol) may reduce salt 



