102 



MINERAL SALTS ABSORPTION IN PLANTS 



Ion 



No" 



Cl" 



Medium concn 

 (m moles) 



30 



0-65 



35 



^-|^ 



FluxesdO" moles/cm per sec) 



Free space 



Protoplasm 



(ion-concn, 



m moles ) 



Sap 



(ion - concn. 



m moles) 



8 0-4 



_L^ (54) — L^ 54 



4 0-25 



-^-- (113) — -^ I 13 



(25) 



206 



(a) 



(b) 



Fig. 35. Measurements of ion fluxes in algal cells. 

 a. Concentrations of ions in the sap of Nitellopsis, and estimated values of the 

 fluxes between the diff'erent kinetic compartments within the cell. Only the 

 ratio of the concentrations of the 3 ions in the protoplasmic non-free space 

 was measured and the concentrations given in brackets are estimated values 

 (redrawn from MacRobbie and Dainty, 1958a); b. Steady-state flux rates of 

 exchange of potassium ions between diff'erent phases of Nitella axillaris cells 

 (Diamond and Solomon, 1959). 



are also involved in movement of chloride into the non-free space 

 from the medium remains uncertain. 



Diamond and Solomon (1959) distinguished three fractions with 

 differing exchangeability in the potassium content of Nitella 

 axillaris. The smallest fraction, containing about 0-1 per cent of 

 the total potassium, exchanges most rapidly (apparent half time of 

 exchange = 23 sec), and is probably located in the cell wall. The 

 second fraction, comprising about 1 -6 per cent of the total, exchanges 

 more slowly (apparent half time = 5 hr) and may represent an 



