Biometric analysis of the relationship between the osmotic pressure of the cell sap and its refractive index

Porovnávacími stanoveniami osmotického tlaku kryskopickou metódou a refraktorického indexu bunkovej ?t'avy listovHordeum sativum Jessem. boli získané ?íselné údaje pre biometrické vyjadrenie závislosti medzi oboma hodnotami. Biometrické vyjadrenie taktie? potyrdilo správnost' stanoviska, podl'a ktorého je zistenie osmotického tlaku bunkovej ?t'avy refrakeiou dostato?ne spol'ahlivé len vtedy, ked' sa pri ňom vychádza z experimentálne stanoveného korela?ného vzt'ahu. ?írka vytvoreného pravdepodobnostného pásu, podl'a vopred zvoleného kritéria spol'ahlivosti, vo smere hlavnej diagonály (osi regresných priamok) korela?ného pol'a ukázala, ?e pravdepodobnostný pás je tým u??í, ?ím je materiál fyziologicky homogennej?í. Rie?enie problému u bunkovej ?t'ávy listov ja?meňa upozornilo, ?e vhodným metodickým prístupom sa dajú aj pri pomerne zlo?itom druhu vytvorit' podmienky pre stanovenie rie?enej korela?nej závislosti. Tým sa sú?asne ukazuje mo?nost' pou?itia refrakeie ako dostato?ne spol'ahlivej metódy pre stanovenie osmotického tlaku bunkovej ?t'avy i u kultúrnych tráv.     

The plant cell pressure probe

The pressure probe is a micro manometer for the simultaneous direct recording and manipulation of plant cell hydrostatic pressure. It is used to map in space and time the turgor pressures of individual cells within tissues and organs of intact plants. This is used to study the hydraulic architecture of tissues, tissue movement and the responses of tissues to water stress. The approach can be augmented by simultaneous measurement of individual cell osmotic pressure. This permits the hydraulic driving forces across selectively permeable membranes and walls to be assessed fully. By manipulating manually the pressure, cell wall elasticity and its properties can also be mapped. Under some conditions this can be extended to plastic behaviour.     

Extraction and analysis of sap from individual wheat leaf cells: the effect of sampling speed on the osmotic pressure of extracted sap

Abstract. A modification to the pressure probe is described which allows very rapid extraction of sap samples from single higher plant cells. The performance of this rapid-sampling probe was assessed and compared with the unmodified probe for cells of both wheat and Tradescantia. Under some conditions, the unmodified probe operated too slowly to avoid dilution of cell sap during the extraction process. This led to values for apparent sample osmotic pressures that were below the turgor pressures for the same cells. The problem was particularly acute in young wheatleaf epidermal cells which are small, elongate and have high turgor pressure. These exhibited rapid water influx when their turgor was depressed during the sampling of their contents (half-time for pressure recovery in wheat cells was less than 1 s while in Tradescantia cells it was 3–5 s). Dilution during sampling was apparently negligible when the rapid sampling probe was used. The study was complemented by a simple model of the way cells dilute during sampling. Quantitative predictions of the model were consistent with our observed findings. The model is used to assess the major factors which determine a cell's susceptibility to dilution during sampling.     

The half-life of a drug in relation to its therapeutic index

A procedure is given for the determination of the effective half-life of a drugin vivo with respect to an arbitrary response. If the half-life of the drug with respect to toxicity is different from that for therapy, the therapeutic index would be expected to depend on the temporal spacing of the dose. Equations are derived for this variation for a special case. This work was carried out under contract with the Medical Division of the Chemical Warfare Service.     

Hydrostatic and osmotic pressure activated channel in plant vacuole

The vacuolar membrane of red beet vacuoles contains a channel which was not gated by voltage or Ca²⁺ ions. Its unit conductance was 20 pS in 200 mM symmetrical KCl solutions. It was stretch activated: the conductance remained constant but the probability of opening was increased by suction or pressure applied to a membrane patch. A 1.5-kNm^-2 suction applied to isolated patches or a 0.08-kNm^-2 pressure applied to a 45-μm diameter vacuole induced an e-fold change in the mean current. A 75% inhibition of the channel current was obtained with 10 μM Gd³⁺ on the cytoplasmic side. The channel was more permeable for K⁺ than for Cl^- (P_K/P_Cl ~ 3). A possible clustering for this channel was suggested by the recordings of the patch current. The channel properties were not significantly affected by a change in sorbitol osmolality in the solutions under isoosmotic conditions, between 0.6 and 1 mol/kg sorbitol. However, the channel was very sensitive to an osmotic gradient. A 0.2-mol/kg sorbitol gradient induced a two-fold increase in unit conductance and a thirty-fold increase in the mean patch current of the channel. A current was measured, when the osmotic gradient was the only driving force applied to the vacuolar membrane. The hydrostatic and osmotic pressure (HOP) activated channel described in this paper could be gated in vivo condition by a change in osmolality, without the need of a change in the turgor pressure in the cell. The HOP channel represents a possible example of an osmoreceptor for plant cells.     

Changes in haemolymph osmotic pressure in Locusta migratoria larvae in relation to feeding

An account is given of the effect of feeding on haemolymph osmotic pressure in larvae of Locusta migratoria. Changes in concentration of solutes and haemolymph volume are investigated and discussed.     

The choice and use of an index of red cell osmotic fragility

Using two techniques, the authors collected replicated data on red cell osmotic fragility of normal Jersey cows having different haemoglobin genotypes. The data were tested against several theoretical distributions. The logistic sigmoid was chosen as a model, the concentration of added salt solution at which 50% haemolysis occurred was taken as an index. Red cells of haemoglobin genotype BB were more fragile than AA , with AB intermediate.     

The freezing point depression of mammalian tissues in relation to the question of osmotic activity of cell fluid

The freezing point depression of freshly excised frozen tissues, pulverized in a hydraulic press or in a mortar, is greater than that of plasma. Even at 0°C. the freezing point depression of such homogenates increases significantly with time. Dilution data indicate that such freezing point data are valid. The presence of intact cells has been shown in smears of tissues pulverized in a mortar, but not in smears of those crushed in a hydraulic press. The osmolarity of various diluent solutions affects the calculated osmotic activity of tissue homogenates presumably because of delayed diffusion between the diluent and cell fluid. With a hypertonic NaCl diluent, spuriously low values of tissue osmotic activity are found from calculations assuming instantaneous mixing between homogenates and diluents. The limitations of data from cryoscopic experiments and from tissue-swelling experiments are discussed in relation to the basic question of whether or not cell fluid is isotonic to extracellular fluid.