Cell envelope phospholipid changes in a moderate halophile during phenotypic adaptation to altered salinity and osmotic stress

Abstract The increased content of negatively-charged phospholipids in membranes of Vibrio costicola grown at high salinities is mediated by increased phospholipid synthesis of phosphatidylglycerol relative to phosphatidylethanolamine. This phenomenon provides a system for investigating the factors involved in triggering and controlling haloadaptation in this moderately halophilic bacterium. We review recent experiments, which show that when subjected to sudden increases in external salinity, V. costicola senses both the absolute NaCl concentration and the magnitude of the salt shift. We show that the latter is sensed at least in part via osmotic pressure effects, since shift-up into sucrose-containing media triggers comparable changes in growth and in phospholipid composition and synthesis.     

The delineation of nuclear boundaries in microscopic images

A semiautomatic procedure for tracking the boundaries of liver nuclei in digitized microscopic images of normally prepared biopsy material is described. The operator selects the nucleus, and a guided sequential search procedure tracks edge segments, which may subsequently be linked to produce a closed or partially open boundary, which is then accepted, completed or rejected by the user.     

Cell Kinetic Studies of the Effect of A Combined Therapy With 1-βd-Arabinofuranosylcytosine (Ara-C) and X-Irradiation On the L1210 Ascites Tumour

Abstract. We studied the effect of combined therapy with X-ray and 1-β-D-arabinofuranosylcytosine (Ara-C); firstly the effect of whole-body X-irradiation alone on the proliferation of the L1210 ascites tumour of the mouse was studied by autoradiographic and cytofluorometric (FCM) methods. the effect of X-irradiation with 4 Gy was mainly a cytostatic one leading to an altered distribution of the cells throughout the cycle due to radiation induced mitotic delay. the cytocidal effect is negligible.
As is known from previous studies (Fietkau, Friede & Maurer-Schultze, 1984) the effect of 200 mg/kg Ara-C consists of an inhibition of DNA synthesis and of killing a considerable portion of the L 1210 cells, predominantly of S phase cells.
With respect to the importance for potential therapeutic regimens, the influence of the sequence and the time interval between the two therapeutic steps on the survival of tumour-bearing mice was studied. Most combination therapies significantly increase the survival of tumour-bearing mice compared to the single therapeutic steps; however, no significant differences between the various combined therapies were found. Whole-body X-irradiation with 4 Gy followed by the application of 200 mg/kg Ara-C 10 hr later resulted in the greatest increase of the mean survival time of tumour-bearing animals, from 13.2 to 17.4 days. It was shown that apart from the cytocidal effect on S-phase cells, Ara-C also kills cells sublethally damaged by a preceding X-irradiation.     

The banded karyotypes of Macaca fuscata compared with Cercocebus aterrimus

The karyotypes of Macaca fuscata and Cercocebus aterrimus are compared after G, C and AgNOR banding. Although it is often assumed that the 42-chromosome monkeys (species of the genera Macaca, Papio, and Cercocebus) are identical at the chromosomal level, a number of clear and consistent differences between the karyotypes of these two taxa are described. These differences include one pericentric inversion and differences in staining intensity, particularly in centromeric and pericentromeric areas. It is probable that high resolution chromosome techniques could reveal more differences between taxa in the 42-chromosome group than are now believed to exist. It is therefore probable that karyological data could provide insight into the phylogenetic relationships in this group of Old World monkeys.     

The synthesis of ATP by the membrane-bound ATP synthase complex from medium 32Pi under completely uncoupled conditions

Previously, we demonstrated that isolated coupling factor 1 can reversibly synthesize bound ATP from "tightly bound" ADP and medium Pi (Feldman, R I., and Sigman, D. S. (1982) J. Biol. Chem. 25, 1676-1683). In order to ensure that the thermodynamic constants derived are relevant to coupled ATP synthesis, we have also studied the reaction on thylakoid membranes. The ATP synthase complex, uncoupled with 20 mM NH4Cl or 0.3% Triton X-100, synthesizes enzyme-bound ATP in a similar manner to coupling factor 1. The pH optimum is 6, the concentration of medium Pi for 50% saturation is 38 mM, and the equilibrium constant for the formation of ATP from bound ADP and Pi is 0.5. It is concluded that the active site responsible for the reaction is not appreciably altered by the dissociation of coupling factor 1 from the membrane or Fo. Thus, either enzyme form can be used to derive data relevant to the mechanism of ATP synthesis. The ability to measure bound ATP synthesis in an energizable system will allow us to probe the effect of membrane energization on the accumulated bound product.     

Effects of Light on Dopamine Metabolism in the Chick Retina

The effect of prolonged exposure to light on the activity of dopaminergic neurons and dopamine (DA) metabolism of chick retinae was investigated. alpha-Fluoromethyldopa, a potent and specific irreversible inactivator of aromatic amino acid decarboxylase, was used to assess DA turnover after inhibition of synthesis, and also to assess in vivo tyrosine hydroxylase activity by dihydroxyphenylalanine accumulation. After 48 h of light exposure, retinal DNA in 12-day-old chicks was about 30% higher (p less than 0.005) whereas dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were elevated two to three times (p less than 0.005) the level of controls kept in the dark for the same period. DA turnover was about twofold faster in the light (t 1/2 = 31 min) than in the dark (t 1/2 = 65 min). Tyrosine hydroxylase, assayed in vitro with saturating levels of cofactor and substrate, increased by about 50% after light exposure. The apparent tyrosine hydroxylase activity in vivo was approximately sixfold higher in the light than the dark. These results are interpreted and discussed in terms of the regulation of DA synthesis, and the use of DOPAC and HVA as indices of DA function in the retina.     

The effect of soil water status on critical phosphorus concentrations inStylosanthes hamata cv. Verano

Summary The effect of soil water status on the critical phosphorus concentration (CPC) determined in apices and whole tops ofStylosanthes hamata cv. Verano was investigated in a glasshouse trial. The species was grown with six rates of P and three ranges of soil water potential and was harvested at 10 and 14 weeks after germination. The CPC of both whole tops and apices decliced between the two harvests. At the first harvest the CPC of both whole tops and apices increased as the soil water potential decreased but at the second harvest there was no effect of soil water potential on CPC. It is suggested that at the earlier harvest water stress was delaying physiological development, resulting in a CPC characteristic of chronologically younger tissue, but that by the second harvest the decline in CPC with age had ceased for all water treatments.     

Circular dichroism of biological membranes: I. Mitochondria and red blood cell ghosts

Improved circular dichroism curves are reported for mitochondria and red blood cell ghosts. The red shift and low amplitudes of the suspension spectra are shown to be due to distortions arising from the particulate nature of the samples. Previously proposed details of membrane structure based on the “red shift” are not supported by the corrected spectra.     

Moisture as a factor influencing the distributions of two species of terrestrial salamanders

Summary Plethodon richmondi shenandoah occurs in at least three geographically isolated talus slopes in Shenandoah National Park, Virginia, U.S.A., each surrounded by a continuous population of Plethodon c. cinereus in the soil outside the talus. Distributions are contiguous but largely non-overlapping. The talus presents a much drier habitat than does the surrounding soil. Four experiments were designed to test the responses of the two species to moisture and substrate. Although shenandoah lives in a habitat generally drier than that of cinereus, both species choose the wet end of a moisture gradient and do not differ significantly in moisture preference. When given choices between a substrate of rock or soil, the two species respond similarly: neither expresses a preference when both substrates are moist and both choose soil over rock as the substrates dry, showing that substrate preference is based on moisture content and not texture. A third experiment demonstrates that cinereus suffers significantly greater mortality and loss of body water when subjected to a drying rock substrate than when subjected to a soil substrate, since the latter holds moisture longer. Thus the talus most likely presents a greater stress of dehydration to salamanders than does the soil. A fourth experiment shows that when forced to dehydrate, shenandoah survives longer, loses significantly less body water per hour, and withstands a greater loss of body water before death than does cinereus.The conclusions drawn are that cinereus inhabits areas of deep soil not due to a preference for that substrate but due to the requirement of a moist substrate, and it cannot enter the talus due to the dry conditions there. P. r. shenandoah, on the other hand, neither prefers the rocky nor the dry conditions of the talus and is probably excluded from the soil by the presence of cinereus. The survival of shenandoah in the talus is due, at least in part, to its ability to withstand the stress of dehydration for a longer period than can cinereus.