Osmotic, adjustment potential

Sharp, R.E., Hsiao, T.C. Silk, W.K. (1988). Growth of the maize primary root at low water potentials. II. Spatial distribution of osmotic adjustment in the growing zone. Plant Physiology, (in press). 

Westgate, M.E. Boyer, J.S. (1985 ). Osmotic adjustment and the inhibition of leaf, root, stem and silk growth at low water potentials in maize. Planta, 164, 540-9. 

Brassica napus cells have been selected for tolerance to Na2S04 (Chandler Thorpe, 1987). When selected cells were compared with non-selected cells in response to Na2S04 salinity the selected cells grew better and showed less negative cell water potential than the non-selected cells. Both cell lines showed osmotic adjustment and proline accumulation. However, proline accumulation was related to inhibition of growth and did not play a significant role in osmotic adjustment. 

Similarly to drought stress, sahnity imposes a water-deficit that results from the relatively high solute concentrations in the soil, but in addition it may cause ion-specific stresses resulting from altered K /Na ratios, and also may lead to a build-up in Na and d concentrations that are detrimental to plants. Plants respond to salinity using two different types of responses. Salt-sensitive plants restrict the uptake of salt and adjust their osmotic potential by the synthesis of compatible solutes (pro-hne, glycinebetaine, sugars, etc.) [19]. 

Aqueous solutions can be modeled by writing a virial equation such as (17.37) in which osmotic pressure replaces pressure. Friedman (1962) describes applications of cluster expansion theory, which include long-range Coulombic potentials as well as short-range square-well potentials that operate when unlike ions approach within the diameter of a water molecule. These models are mathematically quite cumbersome and are not easily used for routine calculations. They do predict the non-ideal behavior of simple electrolytes such as NaCl quite admirably at moderate concentrations however, they use the square-well potential as an adjustable parameter and so retain some of the properties of the D-H equation with an added adjustable term. For this reason these are not truly a priori models. 

The chemiosmotic system of Fig. 1 catalyses the translocation of the chemical groups A, B, H and OH and transforms the chemical work defined by AG into the energetically equivalent osmotic potential in a form that can do external work as the reaction proceeds from left to right. Conversely, the osmotic potential would be converted to chemical bond energy when the reaction progressed from right to left as a result of appropriately adjusting... 

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