Chapter VIII _139— Active Relations 



The mechanism underlying primary ion absorption is very complex and 

 involves the little understood properties of living protoplasm. While the 

 protoplasm must be the locus of the energy release, apparently a higher 

 level of accumulation exists in the vacuole (Hoagland and Broyer, 1942). 

 Though in the initial stages of accumulation by low salt plants, concentra- 

 tion in the protoplasm may greatly exceed that of the vacuole (Brooks, 

 1938) in the steady or equilibrium state the vacuolar concentration is 

 greater. Though this implies accumulation in the cytoplasm, followed 

 possibly by passive release into the vacuole, the end result is equivalent to 

 secretion. Intimately associated with the active process are problems of 

 permeability, interionic relations, m.etabolic level, active water control, etc. 



Steward, et al. (series of papers to 1943) concluded that ion accumu- 

 lation is related to protein metabolism. The capacity to synthesize protein 

 is considered essential to cells that accumulate and retain solutes in their 

 cell sap. 



Accumulation or active solute uptake by plants is an established fact. 

 Until recently workers have directed little attention to the water relations 

 of this process. From the similarity of ion uptake and water secretion one 

 is prompted to ask, if ions are actively absorbed, cannot water also be ac- 

 cumulated by living cells ? Hoagland has stressed the independence of ion 

 and water uptake. Are these processes as independent as might appear? 

 Or may they not be simply different aspects of a single process, the differ- 

 ences in rates being reflections of differences in availability or of transport 

 away from absorbing organs ? 



Steward, Stout, and Preston (1940), as previously noted, observed 

 an anomalous water uptake in potato discs. The presence of potassium 

 accelerated absorption whereas calcium had a depressing effect. Nitrate 

 ions accentuated the acceleration due to potassium. The suggestion is made 

 that in addition to solute accumulation, water absorption may also be re- 

 lated to respiration and protein synthesis. The results, they state "suggest 

 that aerobic respiration, protein synthesis, water absorption, and salt ac- 

 cumulation are all mutually dependent processes which occur in all cells 

 which are not subject to equilibrium conditions but the behavior of which, 

 at constant temperature, is regulated by oxygen tension and the nature and 

 concentration of the salt solution in which they are immersed." 



The relation between water absorption (by roots) and active solute 

 absorption becomes even more intimate in the theories of Lundegardh 

 (1946). Anions are pictured as actively absorbed by the protoplasm, 

 energized by a special "anion respiration," Cations then move more or 

 less passively from negative points on the surface to negative points in the 

 protoplasm, being "dragged along" due to potential differences maintained 

 by anion accumulation. The ions which move from the root hair across 

 the cortex, K% NO3", HCO3", etc., carry with them spheres of water, the 

 amount related inversely to the osmotic pressure of the cell sap. As the 

 ions are permitted to "leak" into the vessels they carry this water along. 

 They carry in addition what Lundegardh terms "extra water," which in- 

 cludes metabolic water, some carried to the roots by sugars, and some due 

 to changes in the swelling power of the protoplasm. In this manner, the 

 bleeding sap (exudate) may be more dilute than the medium bathing the 

 roots. 



Relation to Other Plant Functions: — The possible role of active 

 water control in other plant functions may be briefly indicated. Interrela- 



