Hours In Distilled Water Research Articles

Development of sodium regulation and de novo synthesis of Na+K‐activated ATPase in larval brine shrimp, Artemia salina

AbstractThe development of brine shrimp embryos, A. salina, incubated in media of increasing salinity is delayed as evidenced by decreased emergence and lengthening of the time for excystment. Prehydration of cysts at low temperature (3°C) for four to ten hours in distilled water eliminates asynchrony of the population in regard to emergence and hatching times. Internal concentration glycerol, which controls the rate of hydration of the cyst stage, is markedly affected by external salinity. Water balance in the cyst stage is maintained via the trehalose‐glycerol mechanism which generates a simple passive diffusional gradient across the chitinous shell allowing water to pass. Non‐gaseous solutes, such as sodium and glycerol, do not pass through the chitin‐membrane barrier. Rupturing the shell by emergence initiates the onset of the prenaupliar stage; it is accompanied by the appearance of large amounts of free glycerol in the external media, decreasing levels of internal glycerol, increased concentrations of internal sodium and the first detectable levels of the cationic transport enzyme, Na + K‐ATPase. Continual loss of free glycerol through the cellular and hatching membranes causes the excysting embryo to convert from a trehalose‐glycerol mechanism to a sodium‐mediated transport system in order to maintain larval water balance. Ontogeny of the sodium regulating mechanism requires formation of Na + K‐ATPase. The production of new Na + K‐ATPase, as evidenced by incorporation of 14C‐amino acids into polypeptide subunits and density‐gradient centrifugation of radioactive membrane vesicles rich in Na + K‐ATPase, may play an important role and, if so, it appears to be initiated between E‐1 and E‐2 stages.

Vacuolar and Cytoplasmic Potassium Concentrations in Pea Roots in Relation to Cell-to-Medium Electrical Potentials

The cause of the cell-to-medium electrical potentials of plant and animal cells is incompletely understood. In some cases, the potentials appear to be diffusion potentials in which potassium ions play a major role (3, 7.) This is indicated A) by potentials which are close to the Nernst potentials for potassium and B) by cell-to-medium potentials which become markedly less negative when the external potassium ion concentration is increased (2, 3, 5, 6, 8, 13). Some evidence indicates that the cell-to-medium potentials are not potassium diffusion potentials. In the squid axon, for example, a large potential remains after the axoplasm has been replaced with a potassium-free solution (14) [There is conflicting evidence here however (1)]. Similar results have been found in the case of vacuolar perfusion of Halicystis and Nitella cells (2,15). The cause of the cell-to-medium electrical potentials of higher plants has not been extensively investigated. Evidence for Avena roots indicates that most of the potential difference occurs between the cytoplasm and the medium, that a negligible potential change occurs between the cytoplasm and the vacuole, and that the cell-to-medium potentials of Avena coleoptiles become less negative when the potassium concentration in the medium is increased (5). Also, flame photometric analysis of extracts from roots and tops of pea and oat seedlings show that the potassium concentrations in the cells are much higher than the concentrations of other inorganic ions (7). The above factors indicate that the cell-to-mediuiii potentials could be diffusion potentials caused principally by the cell-to-medium potassium concentration ratios. In pea roots and stems, however, the cellular potassium concentrations under some conditions did not appear to be high enough to be a major factor in a diffusion potential svstem i(4). This finding has to be qualified, however, because only the average cellular potassium concentration was measured and not the specific cytoplasmic and vacuolar concentrations. Because the vacuole is large relative to the cytoplasm, the cellular potassium concentration probably approximates the concentration in the vacuole. If the major potential difference is between the cytoplasm and the medium, as the data for Avena roots suggest, the critical potassium concentration would be in the cytoplasm. In the experiments reported here, an attempt was made to measure this value. Root tissues were obtained from dark-grown 7-day-old Pisurn sativum cv. Alaska seedlings. They had grown for 4 days with their roots in an aerated nutrient solution containing (in mmoles per liter) K0CI, 10; Ca(N03 )2, 10; NaH,PO4, 9.05; Na2HPO4, 0.48; MgSO4, 2.5; (pH 5.3). Previous treatment included washing the seeds and soaking them for 4 hours in distilled water, followed by a 4-day germination period on moistened filter paper. The temperature was 250 for seedling growth and subsequent experimental operations. The potassium concentrations in the cytoplasm and vacuoles of the root cells were derived from measurements of the potential difference between potassium-sensitive and reference microelectrodes which were inserted with micromanipulators into the cytoplasm or vacuole of cortical parenchyma cells. Electrode insertion was approximately perpendicular to the transverse cut surface (5 mm behind the tip) of a root which was in the above nutrient solution in a lucite chamber. Electrode placement was observed with a microscope having a 40X long-working-distance objective (Unitron Company). The potassium-sensitive microelectrodes were prepared from 'Corning NAS 27-4 glass by a method similar to that used by Khuri and co-workers (9). The 1 mm glass tubing was made into microcapillaries with a microelectrode puller like the model PE-2 of Narishige Scientific 'Company. Open tips of the capillaries (diameter less than 1 u) were sealed with a microforge and the tip was assumed to be sealed if water would not move into it by capillarity.

Nutritional requirements for reproduction of a temperature sensitive nematode, reared in axenic culture.

Summary1. Temperature-sensitivity in C. clegans Bergerac is a complex system, composed of a combination of factors, i.e., a) the production of an inhibitory factor in response to higher temperatures, and b) nutritional requirements consisting of proper mineral balance and certain vitamins. 2. Temperature-sensitivity can be overcome by growing the worms at 17°C in 50% heated liver extract + 30% partially defined (peptone) medium and heat-treating them at 27°C for 27 hours in distilled water or in cold blooded Ringers solution. Worms grown in 50% liver extract + water and heat-shocked in distilled water do not reproduce. Deletion and addition of groups of nutrients to the medium indicates that both vitamins and salts are required for protection against heat-shock in distilled water. 3. The need for extra vitamins is eliminated when the worms are grown at 17°C in 50% liver extract + water and heat-shocked in Ringers solution. Comparison of the salts in the peptone medium and Ringers solution suggests that ei...

Studies on the downy mildew of rice plant.

1. In the present paper the writers deal with the results of a study on the oospore germination of Sclerophthora macrospora (Sacc.) Thirum., Shaw et Naras., the causal fungus of downy mildew of rice plant, and inoculation tests by oospores. 2. When the infected leaves were kept on soil flooded with water in autumn, the oospores became germinable at the end of January, and remained viable at least until May. The percentage of germination ranged from 4.08 to 0.14 during January to May. However, oospores of the infected leaves left on dry soil showed no germination. If the infected leaves were burried 2cm deep in the soil, slight germination of oosporores was obtained irrespective of the water condition in soil. 3. Germinability of the oospores was noticed after about 2 months when the infected leaves were kept on soil with flooded water in early March, May, and at the end of August, respectively. The mature oospores in the rotted leaves can germinate within 48 hours in distilled water. 4. Crushing of rotted leaves is not a necessary measure for the germination of the oospores with high germinability. 5. Distilled water may be a favorable medium for oospore germination. Soil extract did not promote germination. Tap water used seems to check the germination. Addition of 5×10-2-10-3 percent peptone in distilled water inhibited the germination. 2% sucrose solution rather accelerated the germination, but it retarded slightly the formation of zoosporangia at the tip of germ tubes. 6. The optimum temperature for the oospore germination seemed to lie between 18-20°C, the highest 25-26°C, and the minimum somewhat lower than 10-12°C. 7. In inoculation experiments to rice seedlings using oospores, a consideraby high perce-ntage of the disease incidence may sometimes be obtained. 8. Owing to the present results, the writers consider the oospores to be fairly important infection source to wild grasses in autumn and to the rice seedlings in the nursery stage.

Staining Myelin Sheaths of Optic Nerve Fibers with Osmium Tetroxide Vapor

OsO4 solution in water, long regarded as the best fixing and staining agent for myelin sheaths, has poor penetrating power. This peculiarity has limited its use to very small pieces of tissue. The vapor from an aqueous solution is known to have a much greater penetrating power for non-neural tissues than the solution itself but nothing has been recorded about its advantages for fixing and staining myelin sheaths of nerve fibers. Difficulties in securing adequate staining of the myelin sheaths in vertebrate optic nerves were overcome largely by the use of the vapor of OsO4. The technic is carried out as follows: 1) suspend a portion of the nerve above a 2% solution of OsO4 for 12-24 hours in an air-tight container at room temperature; 2) wash 4-6 hours in distilled water, dehydrate in ethyl alcohol (50% for 2 hours, 70% for 2 hours, and finally 95% overnight), and transfer to n butyl alcohol (2 changes of 2 hours each); 3) embed in paraffin, section, mount and cover in balsam in the customary manner.