Water Balance in Cucumis Plants, Measured by Nuclear Magnetic Resonance, I

In this paper we demonstrate the study of plant water balanceby the non-invasive measurement of tissue water content andwater flow using proton nuclear magnetic resonance (NMR). Sapvelocity and flux were measured independently in the presenceof an excess of stationary tissue water. The instrumentationdescribed allows automated and unattended measurement of flow-and water content-variables in a well-defined region of theplant over periods of several days, with a time resolution betweensuccessive measurements of c. 5 s. Using this apparatus theeffect of changes in light intensity (day/night rhythm) andrelative humidity on stem tissue water content as well as onthe velocity and flux of xylem sap in the stem were investigatedin a cucumber plant. The results are in agreement with predictionsfrom a simple model for plant water balance, which is basedon water potential, flow rate and resistance to flow. As longas only transpiration is varied, flow rate and water content(or potential) are affected in opposite ways as demonstratedin this paper. In contrast, the model predicts that changesin uptake (resulting from changes in, for example, root resistance)will induce changes in water content and flow in the same direction.An experimental verification of this prediction is given ina subsequent paper, where, in addition, the NMR results arecompared to those obtained with a dendrometer. Key words: Water balance model, Cucumis sativus L., flow, water content, NMR, water balance measurement     

Effects of calcium ionophore, A23187 and calmodulin inhibitors on intercellular communication in the rat myometrium

We have studied the effect of a calcium ionophore, A23187, and the purported calmodulin inhibitors, calmidazolium and chlorpromazine, on direct intercellular communication between smooth muscle cells in the myometrium of delivering rats. The extent of cell-to-cell coupling was determined by exposing one portion of small strips of longitudinal myometrium to 2-[3H] deoxy-D-glucose (2-DG) and determining the distribution and apparent diffusion coefficient (Da) for this tracer after a 5-h period for diffusion. The distribution and Da for 2-DG were significantly (p less than 0.05) reduced by exposure to A23187 in Krebs-Ringer solution with 2.5 mM Ca++, partially reduced in Krebs solution with A23187 and low Ca++ (1-10 microM), but the drug had no effect when used with Ca++-free solutions with [ethylenebis (oxyethylene-nitrilo)] tetraacetic acid (EGTA). The calmodulin inhibitors blocked the effects of A23187 in a dose-dependent fashion, and at higher concentrations, the extent of 2-DG diffusion was not different from that in control tissues. Surprisingly, however, a dose-dependent reduction in coupling was also observed in tissues exposed to the calmodulin inhibitors alone. Structural studies failed to reveal any change in the area of gap junctions between the myometrial cells following the above treatments, suggesting that the reduced exchange of 2-DG resulted from a decrease in the permeability of gap junctions between the muscle fibers.     

TASTE GROUP THRESHOLDS AND SENSORY EVALUATION OF SPANISH WINE VINEGARS

Wine vinegar is a product obtained from wine acidification which contains at least 5% by wt. of acetic acid, in general without any additives or colorings.
Aspects studied in this work include: the determination of the taste group thresholds (geometric mean of the individual best-estimate thresholds "BET") of two different acids (citric and acetic acids) in aqueous solution and spanish vinegars produced from table and sherry wines. The results obtained suggest that wine vinegar can be considered something more than just an acidulant agent.
In order to evaluate differences among wine vinegars, discriminant tests for twenty-five spanish vinegars (sherry, table and flavored vinegars) were applied. Six of the twelve attributes freely chosen by assessors allowed grouping of the spanish wine vinegars according to their sensory aspects.     

In situ hybridization and immunocytochemical localization of SERCA2 encoded Ca2+ pump in rabbit heart and stomach

Heart tissue contains large amounts of the protein encoded by the Ca²⁺ pump gene SERCA2. The SERCA2 RNA can be spliced alternatively to produce mRNA encoding the proteins SERCA2a and SERCA2b which differ in their C-terminal sequences. In this study we report the tissue distribution of SERCA2a and SERCA2b isoforms byin situ hybridization to rabbit heart and stomach. The expression of SERCA2 mRNA was high in myocardial cells, being the highest in the atrial region. In contrast, there was more SERCA2 protein in Western blots in ventricles than in atria. Myocardial cells expressed predominantly the mRNA for the isoform SERCA2a. Whereas the stomach smooth muscle and the neuronal plexus expressed SERCA2 at levels much lower than myocardial cells, the expression was very high in the stomach mucosa. Mucosa contained mainly the mRNA for SERCA2b. From immunocytochemistry it was concluded that the anti-heart SR Ca²⁺ pump antibody IID8 reacted much better with heart and surface mucosal cells in the stomach than with the stomach smooth muscle, and that IID8 reactivity was intracellular. In contrast PM4A2B, an antibody against the plasma membrane Ca²⁺ pump, reacted well with heart and stomach smooth muscle, plexus and mucosa, and its localization appeared to be in the plasma membrane. Thus, stomach smooth muscle expressed SERCA2b mRNA and protein at low levels, mucosa expressed SERCA2b mRNA and protein at high levels, atria and ventricle expressed SERCA2a mRNA and protein at high levels, mRNA being more in atria, but protein being more in ventricles.Deceased August 14, 1992     

Arginine deprivation in KB cells: I. Effect on cell cycle progress

When exponentially growing KB cells were deprived of arginine, cell multiplication ceased after 12 h but viability was maintained throughout the experimental period (42-48 h). Although tritiated thymidine ([(3)H]TdR) incorporation into acid-insoluble material declined to 5 percent of the initial rate, the fraction of cells engaged in DNA synthesis, determined by autoradiography, remained constant throughout the starvation period and approximately equal to the synthesizing fraction in exponentially growing controls (40 percent). Continous [(3)H]TdR-labeling indicated that 80 percent of the arginine-starved cells incorporated (3)H at some time during a 48-h deprivation period. Thus, some cells ceased DNA synthesis, whereas some initially nonsynthesizing cells initiated DNA synthesis during starvation. Flow microfluorometric profiles of distribution of cellular DNA contents at the end of the starvation period indicated that essentially no cells had a 4c or G2 complement. If arginine was restored after 30 h of starvation, cultures resumed active, largely asynchronous division after a 16-h lag. Autoradiographs of metaphase figures from cultures continuously labeled with [(3)H]TdR after restoration indicated that all cells in the culture underwent DNA synthesis before dividing. It was concluded that the majority of cells in arginine-starved cultures are arrested in neither a normal G1 nor G2. It is proposed that for an exponential culture, i.e. from most positions in the cell cycle, inhibition of cell growth after arginine with withdrawal centers on the ability of cells to complete replication of their DNA.     

Are gap junctions necessary for cell-to-cell coupling of smooth muscle?: An update.

Earlier, it was questioned whether gap junctions (GJs) were necessary for cell-cell communication in smooth muscle, and GJs were not seen in some smooth muscles. We reexamined this question in the myometrium and in intestinal smooth muscle, in light of current knowledge of the presence and function of GJs. In the uterus, numerous studies show that an increase in GJ number is associated with the onset of delivery and is required for effective parturition. In all cases, this increase in GJ number and the changes in uterine contractility were correlated with increased electrical and metabolic coupling. Evidence for the much smaller, but detectable, degree of electrical coupling in the preterm uterus is explained by the small (but again detectable) number of GJs present. In the intestine, GJs are readily detected in the circular muscle layer but have not been described in the adjacent longitudinal layer. While our immunohistochemical studies failed to detect GJs in the longitudinal layer, this may not be adequate to prove their absence. Therefore, current knowledge of GJ number and function is adequate to explain cell-cell coupling in the uterus. Although it remains uncertain whether GJs are absent from the longitudinal muscle of the intestine, there is no definitive evidence that cell-cell coupling can occur by means other than GJs.     

Effects of 17 beta-estradiol on myometrial gap junctions and pregnancy in the rat

The effects of estradiol treatment on the development of myometrial gap junctions and premature labour were investigated using timed pregnant rats. In control animals myometrial gap junctions were infrequent between days 17 and 20 of pregnancy, but began to develop on day 21 and were at maximum frequency, size, and membrane area on day 22 during delivery. Gap junctions were completely absent from the myometrium 48 h after delivery. Animals treated with 500 micrograms 17 beta-estradiol/day starting on day 16 of pregnancy developed numerous myometrial gap junctions and delivered their pups prematurely on day 19. Similarly, treatment with 50 micrograms estradiol/day resulted in the development of myometrial gap junctions on day 20 of pregnancy and premature labour. However, treatment with various doses of estradiol up to and including 500 micrograms/day for 3 days beginning 1 day before delivery was not able to maintain the presence of myometrial gap junctions during the postpartum period. These results support the hypothesis that estradiol stimulates the development of myometrial gap junctions and that the presence of gap junctions in the myometrium is a requirement for the occurrence of term, as well as preterm labour. Furthermore, it is evident from this study that the postpartum regression of myometrial gap junctions is not dependent on the decrease in estradiol.