Low growth temperature-induced increase in light saturated photosystem I electron transport is cation dependent

Thylakoid membranes isolated from cold tolerant, herbaceous monocots and dicots grown at 5°C exhibit a 1.5-fold to 2.7-fold increase in light saturated rates of photosystem I (PSI) electron transport compared to thylakoids isolated from the same plant species grown at 20°C. This was observed only when either water or reduced dichlorophenolindophenol was used as an electron donor. The apparent quantum yield for PSI electron transport was not affected by growth temperature. The higher light saturated rates of PSI electron transport in 5°C thylakoids had an absolute requirement for the presence of Na⁺ and Mg⁺². The accessibility of reduced dichlorophenolindophenol to the donor site was not affected by growth temperature since 5°C and 20°C thylakoids exhibited no significant difference in the concentration of this electron donor required for half-maximal PSI activity. The cation dependent higher rates of light saturated PSI activity were also observed when rye thylakoids were developed under intermittent light conditions at 5°C. Thus, this cation effect on PSI activity appeared to be independent of light harvesting complex I and II. The extent of the in vitro reversibility of this cation effect appeared to be limited by an inherent decay process for PSI electron transport. The rate of decay for PSI activity was greatest when thylakoids were isolated in the absence of NaCl and MgCl₂. We conclude that exposure of plants to low growth temperatures induces a reorganization of thylakoid membranes which increases the light saturated rates of PSI electron transport with no change in the apparent quantum efficiency for this reaction. Cations are required to stabilize this reorganization.     

Time of replication of ARS elements along yeast chromosome III.

The replication of putative replication origins (ARS elements) was examined for 200 kilobases of chromosome III of Saccharomyces cerevisiae. By using synchronous cultures and transfers from dense to light isotope medium, the temporal pattern of mitotic DNA replication of eight fragments that contain ARSs was determined. ARS elements near the telomeres replicated late in S phase, while internal ARS elements replicated in the first half of S phase. The results suggest that some ARS elements in the chromosome may be inactive as replication origins. The actively expressed mating type locus, MAT, replicated early in S phase, while the silent cassettes, HML and HMR, replicated late. Unexpectedly, chromosome III sequences were found to replicate late in G1 at the arrest induced by the temperature-sensitive cdc7 allele.     

Methicillin resistance in Staphylococcus epidermidis. Relationship between the additional penicillin-binding protein and an attachment transpeptidase

The penicillin-binding proteins (PBP) of a methicillin-resistant strain of Staphylococcus epidermidis, 100,604 p+m+ and a non-isogenic sensitive strain, p-m- were characterised. The presence of a novel PBP, produced by the methicillin-resistant strain of S. epidermidis, with an Mr identical to that of PBP2' in Staphylococcus aureus 13,136 p-m+, was revealed by sodium dodecyl sulphate/polyacrylamide gel electrophoresis and subsequent fluorography of solubilised membrane proteins isolated from cells labelled with [3H]benzylpenicillin. This novel PBP was only detected in cells which had been grown at 30 degrees C, in media containing beta-lactam antibiotic and 5% NaCl. The sensitivity of an attachment transpeptidation reaction measured under non-growing conditions in the sensitive and resistant strains indicated that the novel PBP catalysed this reaction. The similarity of radiolabelled peptides resulting from partial proteolytic digestion of the novel PBP in S. epidermidis 100,604 p+m+ and from PBP2' in S. aureus 13,136 p+m+ lends support to the theory that the additional DNA encoding PBP2' in S. aureus and the same protein in S. epidermidis has been passed to both species from an unknown source. Studies of the development and loss of resistance of attachment transpeptidase activity, and the appearance and disappearance of the novel protein when cultures of the resistant strain were transferred from conditions allowing the expression of resistance to those not allowing such expression and vice-versa, indicated that there was a strong correlation between the presence of PBP2' and the degree of resistance of the attachment transpeptidation reaction and that the production of this protein was affected by temperature at a regulatory or genetic level. Studies on the induction and loss of beta-lactamase activity and of the novel PBP when the resistant strain was grown in the presence or absence of beta-lactam antibiotics at either 40 degrees C or 30 degrees C suggests that there is little relationship between the production of this enzyme and of PBP2' other than the fact that beta-lactam antibiotics are common inducers of both.     

Expression of HOX homeogenes in human neuroblastoma cell culture lines

Mammalian genes containing a class-I homeobox (HOX genes) are highly expressed in the embryonic nervous system. As a first step towards the molecular analysis of the role these genes play in neural cells, we studied the expression of four human HOX genes in five neuroblastoma (NB) cell lines - SK-N-BE, CHP-134, IMR-32, SK-N-SH and LAN-1 - during the process of differentiation induced by treatment with retinoic acid (RA). The four genes, HOX1D, 2F, 3E and 4B, located at corresponding positions in the four HOX loci, share a high degree of sequence similarity with the Drosophila Deformed homeotic gene and constitute a homology group, group 10. One of these genes, HOX1D, is not expressed in the cells used, whereas the other three are highly expressed in untreated and RA-induced NB cells, even though the expression pattern in the various lines is slightly different for the three genes. Our analysis reveals a complex and specific expression pattern in these lines, paving the way to an identification of different NB-cell populations by means of specific HOX gene expression schemes. On the other hand, in every line studied, morphological maturation toward a neuronal differentiated phenotype appears to be associated with increased HOX gene expression.     

Pericentric inversion of chromosome 19 in three families

Summary Pericentric inversion of chromosome 19 has been found in several members of three unrelated families from a restricted geographical region. In one of the families, an additional pericentric inversion of chromosome 9 was observed. Reproductive problems, multiple abortions in two families and a neonatal death in the third, were present. A review of previously described cases is included, and the genetic risk connected with this type of rearrangement is also discussed.     

Brain Metabolism and Intracellular pH During Ischaemia: Effects of Systemic Glucose and Bicarbonate Administration Studied by 31P and 1H Nuclear Magnetic Resonance Spectroscopy In Vivo in the Lamb

Brain metabolism and intracellular pH were studied during and after episodes of incomplete cerebral ischaemia in lambs under sodium pentobarbitone anaesthesia. 31P and 1H magnetic resonance spectroscopy was used to monitor brain pHi and brain concentrations of inorganic phosphate (Pi), phosphocreatine (PCr), beta-nucleoside triphosphate (beta NTP), and lactate. Simultaneous measurements were made of arterio-cerebral venous concentration differences (AVDs) for oxygen, glucose, and lactate. Cerebral ischaemia was induced by a combination of bilateral carotid clamping and hypotension, and the acute effects of systemic administration of glucose and sodium bicarbonate were examined. The molar ratio of glucose to oxygen uptake by the brain (6G/O2) increased above unity during cerebral ischaemia. Statistically significant AVDs for lactate were not observed. Cerebral ischaemia was associated with a reduction in brain pHi PCr/Pi ratio, and an increase in brain lactate. No effect of arterial plasma glucose on brain lactate concentration or brain pHi was evident during cerebral ischaemia or in the postischaemic period. Administration of sodium bicarbonate systemically in the postischaemic period was associated with a rise in arterial and brain tissue PCO2. A fall in brain pHi occurred which was attributable in part to coincidental brain lactate accumulation. The increase in brain lactate measured by 1H nuclear magnetic resonance in vivo during ischaemia was insufficient to account for the change in buffer base calculated to have occurred from previous estimates of brain buffering capacity.     

Influence of pH,exchangeable aluminium and 0.02M CaCl2-extractable aluminium on the growth and nitrogen-fixing activity of white clover (Trifolium repens) in some New Zealand soils

The effects of soil acidity on the growth and N₂-fixing activity of white clover in seven acid topsoils and subsoils of New Zealand were investigated using a glasshouse experiment.The application of phosphate (Ca(H₂PO₄)₂) to the soils resulted in very large increases in white clover growth on all soils. The application of phosphate, as well as increasing P supply, also decreased 0.02M CaCl₂-extractable Al levels, but had little effect on exchangeable Al levels.Where adequate phosphate was applied, increasing rates of lime (CaCO₃) resulted in increased plant growth on most soils. N₂[C₂H₂]-fixing activity was increased by the first level of lime for one soil, but generally remained approximately constant or declined slightly at higher rates of lime. Up to the point of maximum yield, white clover top weight was more highly correlated with 0.02M CaCl₂-extractable soil Al than with exchangeable Al or pH. At pH values greater than 5.5, plant yield declined on some soils, apparently because of Zn deficiency. The data suggest that white clover is unlikely to be affected by Al toxicity at 0.02M CaCl₂-extractable Al levels of less than about 3.3 g g^–1. However, there were differences between soils in apparent plant tolerance to 0.02M CaCl₂-extractable Al, which appeared to be caused by differing C levels in the 0.02M CaCl₂ extracts.     

IFN-gamma treatment of K562 cells inhibits natural killer cell triggering and decreases the susceptibility to lysis by cytoplasmic granules from large granular lymphocytes

Pretreatment of human K562 leukemia cells with rIFN-alpha and rIFN-gamma resulted in decreased susceptibility to lysis by human peripheral blood NK cells. The reduction of NK-susceptibility after IFN treatment was not due to a general effect of IFN on the stability of the cell membrane because the susceptibility of K562 cells to lysis by antibodies plus C, distilled water, or lysolecithin was unaffected. Binding studies with effector cell preparations enriched for NK cells with large granular lymphocyte morphology revealed no difference in binding to control and IFN-gamma-treated target cells. The sensitivity to soluble NK cytotoxic factors was not affected significantly by the IFN treatment. In contrast, the susceptibility of IFN-treated target cells to the cytotoxic activity of purified cytoplasmic granules from a rat large granular lymphocyte tumor was significantly reduced, indicating that the IFN-induced resistance acted at the level of susceptibility to the lytic mechanism of NK cells. However, IFN-alpha was more effective than IFN-gamma in inducing resistance to the cytoplasmic granules although resulting in only a weak resistance in the cell-mediated cytotoxic assay. IFN-gamma but not IFN-alpha caused a reduction in the frequency of effector cells that had reoriented their Golgi apparatus toward their bound target cell. In addition, IFN-gamma treated K562 cells failed to elicit an influx of Ca2+ into effector cells. Taken together, the results suggest that IFN-gamma in addition to an increased resistance to the lytic molecules released by NK cells can also induce changes in the target cells which prevent the triggering and activation of the effector cell.