Levels Of Osmotic Stress Research Articles

CORNEAL TRANSPARENCY CHANGES RESULTING FROM OSMOTIC STRESS

Corneal thickness and transparency changes were measured following exposure of the cornea to various levels of osmotic stress. Bathing the cornea in hypotonic solutions of NaCl caused an increase in corneal thickness and light scatter within the cornea. Transparency changes with hypotonicity were determined by comparing the relative brightness of haloes around a bright lamp source for the various concentrations of NaCl solutions. Corresponding corneal thickness changes were determined by pachometry. A nearly linear relationship was found between solution hypotonicity and the degree of corneal swelling, whilst an exponential relationship was found between hypotonicity and relative halo brightness. The rate of corneal recovery from osmotic stress was found to be constant with different degrees of tonicity, although the rate of thickness recovery was much slower than the recovery from haloes.

Corneal transparency changes resulting from osmotic stress

Abstract Corneal thickness and transparency changes were measured following exposure of the cornea to various levels of osmotic stress. Bathing the cornea in hypotonic solutions of NaCl caused an increase in corneal thickness and light scatter within the cornea. Transparency changes with hypotonicity were determined by comparing the relative brightness of haloes around a bright lamp source for the various concentrations of NaCl solutions. Corresponding corneal thickness changes were determined by pachometry. A nearly linear relationship was found between solution hypotonicity and the degree of corneal swelling, whilst an exponential relationship was found between hypotonicity and relative halo brightness. The rate of corneal recovery from osmotic stress was found to be constant with different degrees of tonicity, although the rate of thickness recovery was much slower than the recovery from haloes.

Water Relations in Soils as Related to Plant Communities in Ruby Valley, Nevada

Distinct patterns of vegetation on ancient lake sediments in Ruby Valley, Nev., define differences in soil-water-plant relations resulting either from differences in depth to ground water or from differences in water-retention capacities of soils deriving water only from precipitation. In order of increasing depth to ground water, dominant plant species are Juncus balticus, Distichlis stricta, Potentilla fruticosa, Elymus cinereus, Sarcobatus vermiculatus, and Chrysothamnusnauseosus. Dominant species on soils in order of increasing water-retention capacity are Artemesia tridentada nova, Chrysothamnus viscidiflorous pumilus, Ceratoides lanata, A rtemesia tridentada tridentada, A triplex nuttallii gardneri, and Atriplex confertifok Minimum and maximum levels of soil-water stress measured were systematically related to waterretention capacities of soils. A relationship was defined that permits approximation of amounts of water evapotranspired by different plant communities from percent of area under live plant cover. There are separate relationships, relating plant cover to amounts of plant stress or to amount of water evapotranspired, for habitats that receive water from the water table and those that do not. Levels of osmotic stress encountered in surface soils appear to influence plant-community distribution. Plant communities found in habitats ranging from mesic to xeric, and on sediments ranging from clay to gravel in Ruby Valley, Nev., (Fig. 1) provided an opportunity to investigate soil-waterplant relationships under a wide range of conditions. The information obtained is directly applicable to similar high valleys in the Great Basin. Knowledge obtained concerning mechanisms of moisture retention by soils and its subsequent depletion by evapotranspiration has even wider potential for application.

Effect of water stress and gibberellic acid on germination of flax, sesame and onion seeds

The effects of different osmotic stresses (from 0 to –8× 105 Pa) obtained with NaC or polyethylene glycol 6000 solutions on the germination of flax, sesame and onion seeds were investigated. The effect of presoaking with gibberellic acid (GA3) on the germination of the above mentioned seeds was also studied.It was found that the rate of seed germination and the final germination percentages as well as the amount of water absorbed by the seeds were considerably lowered with the rise of osmotic stress levels whatever the stress agent used, more considerable reduction was obtained under polyethylene glycol 6000 than under NaCl.Presoaking with gibberellic acid increased the rate and the final germination percentage of osmotically stressed flax and sesame seeds, while those of stressed onion seeds were slightly retarded.

Teleost chloride cell. I. Response of pupfish Cyprinodon variegatus gill Na,K-ATPase and chloride cell fine structure to various high salinity environments.

Certain euryhaline teleosts can tolerate media of very high salinity, i.e. greater than that of seawater itself. The osmotic gradient across the integument of these fish is very high and the key to their survival appears to be the enhanced ability of the gill to excrete excess NaCl. These fish provide an opportunity to study morphological and biochemical aspects of transepithelial salt secretion under conditions of vastly different transport rates. Since the cellular site of gill salt excretion is believed to be the "chloride cell" of the branchial epithelium and since the enzyme Na,K-ATPase has been implicated in salt transport in this and other secretory tissues, we have focused our attention on the differences in chloride cell structure and gill ATPase activity in the variegated pupfish Cyprinodon variegatus adapted to half-strength seawater (50% SW), seawater (100% SW), or double-stregth seawater (200% SW). The Na,K-ATPase activity in gill homogenates was 1.6 times greater in 100% SW. When 50% SW gills were compared to 100% SW gills, differences in chloride cell morphology were minimal. However, chloride cells from 200% SW displayed a marked hypertrophy and a striking increase in basal-lateral cell surface area. These results suggest that there are correlations among higher levels of osmotic stress, basal-lateral extensions of the cell surface, and the activity of the enzyme Na,K-ATPase.