230 Mineral Nutrition of Plants 



protoplasm and the migrating constituent. Labile vacuolar solute of 

 individual cells may be retransported where the external supply be- 

 comes limiting. Under these conditions, the activity gradient of the 

 solute constituent is reversed between the aqueous phases of the lumen 

 and protoplasm and renewed movement to other loci in the symplast 

 may occur ( 1, 2, 3, 21, 32, 35, 42, 43, 68, 92) . 



The effects of a reduced rate of oxidative metabolism (attained by 

 reduction of either the aerobic or temperature level of the external 

 medium and internal tissue system) on inorganic solute accumulation 

 were discussed earlier and are exemplified in Figures 8A, 8B, and 10, 

 and in Table VI. The effect of an impaired rate of oxidative metabolism 

 on inorganic solute accumulation has also been studied through the use 

 of respiratory inhibitors. The effect of cyanide in the external bathing 

 medium of roots on potassium and bromide migration is shown in 

 Table VI, from Hoagland and Broyer (32). Here, comparison may be 

 made between the effects of reduced aeration and the application of 

 cyanide. These treatments similarly lead to a marked reduction in ac- 

 cumulation of inorganic solute, while at the same time the usually 

 enhanced respiration is inhibited. The cyanide impairment of accumu- 

 lation and respiration is like an induced anaerobiosis. Similar observa- 

 tions have been made by Lundegardh (43, 44), Machlis (49), and 

 Milthorpe and Robertson (5/). Lundegardh (46) and Machlis have 

 observed inhibition of enhanced respiration as well as accumulation 

 of inorganic solute where other steps in the respiratory cycle are blocked 

 (Figure 22). Interference with glycolysis and either the dehydrogenase 

 or oxidase systems may inhibit inorganic solute accumulation. It 

 should be noted in passing that with cyanide a concomitant reduc- 

 tion in permeability per se is possible. This is similar to effects produced 

 with nitrogen gas, where relatively high concentrations of potassium 

 bromide are applied. The reduced accumulation of inorganic solute by 

 cyanide treatment has led Lundegardh (43, 44) to propose that the 

 energy transfer to absorption is concerned particularly with the terminal 

 oxidase system of roots, especially the cytochrome-cytochrome oxidase 

 system. His detailed theory of the accumulation-respiration process 

 (42,43) concerns primarily the anion of an inorganic solute. He con- 

 siders the energy expended to be restricted to the migration of anions 



