Chapter VIII 



141 



Active Relations 





Blackman favored theory No. 2, where a steady concentration differ- 

 ence would be maintained by osmotic work requiring energy. Evidence 

 supporting this view has been supplied by Osterhout (1947&). By treat- 

 ing one end of a Nitella cell with an isotonic sucrose solution, the internal 

 osmotic pressure at that end was apparently increased. On removal of the 

 sugar solution, so that water completely surrounded the cell, water entered 

 at the treated end and was expelled at the other. 



Mechanisms : — Few mechanisms have been proposed to account for 

 the active regulation of water in living organisms. There has been more 

 speculation on active solute uptake than on water absorption, first, because 

 of its relative importance in the nutrition of plants, and, second, due to 

 the paucity of evidence on active water relations. Especially is this true in 

 the plant field where there is little clear evidence for active water regula- 

 tion. Eaton (1943) thinks there are insufficient data to warrant postulat- 

 ing "uncertain physical and chemical forces" in such plant functions as 

 bleeding and root pressure. 



Some have attacked the concept of "vital" functions in physiology as 

 unnecessary and even absurd. They imply a meaning different than the 

 one used in this chapter. Although our usage of the term indicates the lack 

 of a mechanical explanation at the present time, it presumes that an ex- 

 planation may be forthcoming. To us, the term "active" implies a process 

 involving the utilization of metabolic energy. In this sense salt accumula- 

 tion and water secretion are both active processes. 



Adolph (1943, p. 255) comments that, in addi- 

 tion to osmotic pressure, "other sorts of forces, both 

 known and unknown to physicists, may be simul- 

 taneously present," and he is not optimistic that all 

 of them are ever identified. 



Anomalous osmosis might prove a starting point 

 for an attack on active cell processes, for, in it, water 

 moves in a direction contrary to that expected on the 

 basis of concentration differences. Anomalous os- 

 mosis is a well-established phenomenon. It may be 

 due to processes of the nature of electroosmosis or 

 "anaphoresis" as described by Osterhout and Mur- 

 ray (1939). They used the apparatus diagrammed 

 in Figure 40 in which A represents an aqueous solu- 

 tion of trichloracetic acid separated from water, C, 

 by a layer of guaiacol, B. As expected, acid moved 

 to the right. Water, however, moved in the same 

 direction at a greater rate so that its mol fraction in 

 A decreased. The probable mechanism is that water 

 of hydration is carried along with the solute. Cal- 

 culations proved that over 25 mols of water would 

 have to be transported by 1 mol of acid to account 

 for some of the results obtained. Since hydration 

 did not remain constant, definite hydrates were probably not concerned. 



Some have considered that electroosmosis may be a major factor in con- 

 trolling the water balance of cells. It may act to implement osmotic pres- 

 sure (positive anomalous osmosis), or to oppose it (negative anomalous 

 osmosis). Under proper conditions a transport of water through a mem- 



f 



/? 



I 



Fig. 40. — Apparatus 

 for demonstrating "ana- 

 phoresis." A, an aqueous 

 solution of trichloracetic 

 acid; B, a layer of guaia- 

 col; C, a layer of water. 

 From Osterhout and 

 Murray (1940). 



