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Codium decorticatum maintains its internal osmotic pressure 2.3 bar above the osmotic pressure of the external medium, which results in a hydrostatic pressure difference (turgor) of 2.3 bar. During hypoosmotic stress the primary mechanism for decreasing the internal osmotic pressure is a decrease in active Cl influx. The decreased Cl influx is accompanied by a 6.9 mV depolarization of the negative vacuole potential, while there is no consistent change in the protoplast resistance. The net Cl efflux which results is balanced primarily by a passive net loss of K. During hyperosmotic stress the Cl influx increases, accompanied by a slight (2.6 mV) hyperpolarization and a decrease of 90 Ω cm in the membrane resistance. A passive net uptake of Na accompanies the net active influx of Cl. Following the restoration of normal turgor, which requires about 2 hr, concentrations of Na and K are slowly readjusted over a period of about 30 hr until the normal K/Na ratio of 1.0 is restored. Codium regulates its turgor as rapidly in the dark as in the light, which suggests that the Cl pump is not dependent directly on photosynthesis for its energy supply. [ABSTRACT FROM AUTHOR]

The relationship between the rate of Cl transport and the electrical properties of Halicystis parvula was investigated. Three metabolic inhibitors-darkness, cyanide (2 mm), and low temperature (4°C)-all rapidly and reversibly reduce both the short circuit current (SCC), which is a measure of net Cl transport, and the vacuole electrical potential ( PD). Plotting the PD vs. SCC for inhibited cells yields a linear regression with a y-intercept of zero. The PD is also greatly reduced when the [Cl] of the external medium is lowered. Raising the external [K] produces an appreciable, but less than Nernstian, depolarization, while increasing the external [H] tenfold has no net effect on the PD. Decreasing the external [Na] by tenfold produces only a slight depolarization. Thus, the outer plasma membrane appears to be moderately selective for K over Na or H. The effects of ion substitutions in the vacuolar perfusing solutions on the PD reveal that the vacuolar membrane does not discriminate electrically between Cl and the much larger anions, isethionate and benzenesulfonate, or between Na and K. The data suggest that in internally perfused cells of H. parvula generation of the PD of −50 to −60 mV by a transport system involving only electroneutral pumps is unlikely and that most of this PD is generated by an electrogenic Cl pump. [ABSTRACT FROM AUTHOR]

The current-voltage ( I-V) relationships for internally perfused and nonperfused cells of Halicystis parvula were determined. In both types of cells the I-V curve shows a conspicuous region of negative slope, beginning at vacuole potentials around −30 mV and continuing to values of +20 to +40mV. The negative slope in perfused cells is abolished by the metabolic inhibitors, darkness and low temperature. In order to determine the origin of this negative slope, we measured the voltage sensitivity of the unidirectional fluxes of Cl, Na and K in perfused cells. The results show that the Cl influx, which is mediated primarily by a Cl pump, increases as the vacuole potential is clamped at increasingly more negative values up to −50 mV, while the other fluxes measured changed in the directions predicted by the change in electrical driving force. The voltage sensitivity of the Cl pump quantitatively accounts for the negative slope of the I-V curve. Also, we observed a large transient outward current of 10-20-sec duration following an abrupt depolarization by voltage clamping. This transient current was reduced or abolished by low temperature, which suggests that it may be due to the voltage-sensitive Cl pump. Finally, we found an inverse relationship between the transprotoplasm resistance ( R) and the PD under standard conditions, which suggests that the activity of the electrogenic Cl pump lower R, i.e., it is a conductive pump. [ABSTRACT FROM AUTHOR]

Ionic composition and turgor pressure in the giant celled marine alga, Valonia macrophysa, were measured at environmental salinities ranging from 15‰ to 60‰ (11-44 atm). The steady-state turgor pressure, which is normally about 1.5 atm, changes only 2.5 atm in response to a 25 atm change in seawater osmotic pressure. Thus, turgor regulation is 90% effective. The salts important in turgor regulation are KCl and NaCl. During turgor regulation changes in intracellular KCl concentration account for 85% of the change in sap osmolality, and changes in NaCl account for the remaining 15%. Potassium is actively transported into the vacuole, whereas chloride appears to be passively transported as the counter ion. Thus, potassium transport, which we have shown previously to be sensitive to the turgor pressure, accounts for most of the turgor regulation at all salinities. [ABSTRACT FROM AUTHOR]

Codium decorticatum regulates its internal ionic composition and osmotic pressure in response to changes in external salinity. Over a salinity range of 23 to 37‰ (675 to 1120 mosmol/kg) Codium maintains a constant turgor pressure of 95 mosmol/kg (2.3 atm), observed as a constant difference between internal and external osmotic pressures. The changes in internal osmotic pressure are due to changes in intracellular inorganic ions. At 30‰ salinity the major intracellular ions are present in the following concentrations (mmol/kg cell HO): K, 295; Na, 255; Cl, 450. At different salinities intracellular ion concentrations remain in constant proportion to the external ion concentrations, and thus the equilibrium potentials are approximately constant. The potential difference between the vacuole and seawater (−76 mV), which is predominantly a K diffusion potential, is also constant with changing salinity. Comparison of the equilibrium potentials with the vacuole potential suggests that Cl is actively absorbed and Na actively extruded, whereas K may be passively distributed between the vacuole and seawater. Turgor pressure does not change with environmental hydrostatic pressure, and increasing the external osmotic pressure with raffinose elicits a response similar to that obtained by increasing the salinity. These two results suggest that the stimulus for turgor regulation is a change in turgor pressure rather than a change in internal hydrostatic pressure or ion concentrations. [ABSTRACT FROM AUTHOR]

The marine alga Valonia macrophysa an inhabitant of shallow subtropical waters, is subjected to sudden dilutions of external seawater during rain showers. This study describes the mechanisms involved in turgor pressure regulation following acute hyposmotic shock. Turgor regulation is 88% effective and complete within 4 hr following hyposmotic shocks of up to −10 bar. Loss of vacuolar K, Na and Cl accounts for the decrease in vacuolar osmotic pressure associated with turgor regulation. A novel mechanism of turgor regulation is exhibited by Valonia macrophysa given hyposmotic shocks greater than about −4 bar. Such an osmotic shock causes cell wall tension to increase above a critical value of about 6×10 dyne/cm, whereupon the protoplasm ruptures and the cell wall stretches irreversibly at a localized site. The protoplasm rupture is suggested by (1) a large abrupt increase in K efflux (as measured byRb), (2) a rapid decrease in turgor pressure as measured with a pressure probe, and (3) sudden depolarization of the vacuole potential. Evidence for an increase in cell wall permeability includes efflux from the vacuole of dextran (mol wt 70,000), which normally has a very low cell wall permeability, and scanning electron micrographs which show a trabeculated scar area in the cell wall. This mechanism of turgor regulation is physiologically important because 98% of the cells regained normal growth rate and turgor following acute osmotic shock. [ABSTRACT FROM AUTHOR]

Acquiring and merging companies are beginning to realize that maintaining the morale of surviving managers is vital to the successful conclusion of an ownership changeover. Downsizing, layoffs, and their concurring increased workload may, however, have some positive effects on the remaining staff. The key to morale maintenance is systematic preparation for change. This article discusses this need and recommends steps to assist companies in effectively implementing mergers and acquisitions. Communication must be planned and well executed. A new strategic plan should be developed and shared with the acquired and the acquiring company. Flexibility and creativity are needed when dealing with job changes. Finally companies must invest in development and retraining of the survivors of a merger or acquisition. [ABSTRACT FROM AUTHOR]