Influence of light on the heat sensitivity of the photosynthetic apparatus in isolated spinach chloroplasts

The most heat-sensitive functions of chloroplasts in Spinacia oleracea L. including the stromal carboxylation reaction, the light-induced electrical field gradient across the thylakoid membrane, as well as the overall photosynthetic CO₂ fixation were less affected by heat if chloroplasts were heated in the light: 50% inactivation occurred around 35°C in the dark and around 40°C in the light. Relative low light intensities were sufficient to obtain optimal protection against heat. In contrast, the light-induced ΔpH across the thylakoid membrane, the photophosphorylation, and the photochemical activity of photosystem II which were less sensitive to heat in the dark (50% inactivation above 40°C) were not protected by light. Photosystem II even was destabilized somewhat by light.

The effect of light on the heat sensitivity of the water-splitting reaction was dependent on the pH in the medium. Protection by light only occurred at alkaline pH, in which case heat sensitivity was high (50% inactivation at 33°C in the dark and at 38°C in the light). Protection was prevented by uncouplers. At pH 6.8 when the heat sensitivity was low in any case (50% inactivation at 41°C in the dark), light had no further protecting effect.

Protection by light has been discussed in terms of light-induced transport of protons from the stroma to the thylakoid space and related ion fluxes.

     

Revertants of Adenovirus Type 12-Transformed Hamster Cell Line T637 as Tools in the Analysis of Integration Patterns

Spontaneously arising morphological revertants of the adenovirus type 12 (Ad12)-transformed hamster cell line T637 had been previously isolated, and it had been demonstrated that in these revertants varying amounts of the integrated Ad12 genome were eliminated from the host genome. In this report, the patterns of persistence of the viral genome in the revertants were analyzed in detail. In some of the revertant cell lines, F10, TR3, and TR7, all copies of Ad12 DNA integrated in line T637 were lost. In lines TR1, -2, -4 to -6, -8 to -10, and -13 to -16, only the right-hand portion of one Ad12 genome was preserved; it consisted of the intact right segment of Ad12 DNA and was integrated at the same site as in line T637. In revertant lines G12, TR11, and TR12, one Ad12 DNA and varying parts of a second viral DNA molecule persisted in the host genome. These patterns of persistence of Ad12 DNA molecules in different revertants supported a model for a mode of integration of Ad12 DNA in T637 hamster cells in which multiple (20 to 22) copies of the entire Ad12 DNA were serially arranged, separated from each other by stretches of cellular DNA. The occurrence of such revertants demonstrated that foreign DNA sequences could not only be acquired but could also be lost from eucaryotic genomes. There was very little, if any, expression of Ad12-specific DNA sequences in the revertant lines TR7 and TR12. Moreover, Ad12 DNA sequences which were found to be undermethylated in line T637 were completely methylated in the revertant cell lines G12, TR11, TR12, and TR2. These findings were consistent with the absence of T antigen from the revertant lines reported earlier. Hence it was conceivable that the expression of integrated viral DNA sequences was somehow dependent on their positions in the cellular genome. In cell line TR637, the early segments of Ad12 DNA were expressed and undermethylated; conversely, in the revertant lines G12, TR11, TR12, and TR2, the same segments appeared to be expressed to a limited extent and were strongly methylated.     

Participation of L-ascorbate:ferricytochrome b5 oxidoreductase in ascorbate-dependent fatty acid desaturation of rat liver microsomes.

The microsomal enzyme ascorbate-cytochrome b5 reductase participates in the ascorbate-dependent fatty acid desaturation. Three pieces of evidence are given for this statement: 1) Comparison of the rate of ascorbate-dependent oleate formation with the rate of reduction of cytochrome b5 in microsomes and in the isolated detergent form shows that only the enzymatic reduction of cytochrome b5 is fast enough to support oleate formation; 2) added enriched ascorbate-cytochrome b5 reductase increases the rate of return of stearoyl-CoA oxidised cytochrome b5 back to the reduced state; 3) addition of enriched ascorbate-cytochrome b5 reductase increases the rate of ascorbate-dependent oleate formation in rat liver microsomes.     

Incidence of Listeria monocytogenes in Nature

During a research project on the occurrence of Listeria monocytogenes 194 strains were isolated in southern West Germany during the years 1972 to 1974: 154 from soil and plant samples (20.3%), 16 from feces of deer and stag (15.7%), 9 from old moldy fodder and wildlife feeding grounds (27.2%), and 8 from birds (17.3%). The highest number of isolates was obtained from uncultivated fields. The beta-hemolytic serovars 1/2b and 4b were predominant; other serovars (some of them identified for the first time), including nonhemolyzing strains, have been encountered frequently. It is suggested that Listeria monocytogenes is a saprophytic organism which lives in a plant-soil environment and therefore can be contracted by humans and animals via many possible routes from many sources.     

Correction to: Integrative transcriptomics reveals genotypic impact on sugar beet storability

Plant Molecular Biology - In the above mentioned publication, part of Fig. 6B was distorted (extra diagonal lines appeared). The original article has been corrected and the proper version...     

Efficient colonization of the endophytes Herbaspirillum huttiense RCA24 and Enterobacter cloacae RCA25 influences the physiological parameters of Oryza sativa L. cv. Baldo rice

Several important bacterial characteristics, such as biological nitrogen fixation, phosphate solubilization, 1-aminocyclopropane-1-carboxylate deaminase activity and production of siderophores and phytohormones, can be assessed as plant growth promotion traits. Our aim was to evaluate the effects of nitrogen fixing and indole-3-acetic acid (IAA) producing endophytes in two Oryza sativa cultivars (Baldo and Vialone Nano). Three bacteria, Herbaspirillum huttiense RCA24, Enterobacter asburiae RCA23 and Staphylococcus sp. 377, producing different IAA levels, were tested for their ability to enhance nifH gene expression and nitrogenase activity in Enterobacter cloacae RCA25. Results showed that H. huttiense RCA24 performed best. Improvement in nitrogen fixation and changes in physiological parameters such as chlorophyll, nitrogen content and shoot dry weight were observed for plants co-inoculated with strains RCA25 and RCA24 in a 10:1 ratio. Based on confocal laser scanning microscopy analysis, strain RCA24 was the best colonizer of the root interior and the only IAA producer located in the same root niche occupied by RCA25 cells. This work shows that the choice of a bio-inoculum having the right composition is one of the key aspects to be considered for the inoculation of a specific host plant cultivar with microbial consortia.     

SERS‐based biosensor for Alzheimer disease evaluation through the fast analysis of human serum

Alzheimer disease (AD) is the most common form of dementia in the elderly, progressively affecting the cognitive functions with a complex diagnostic procedure that limits the time for a prompt intervention. In this study we optimized a reliable protocol for the analysis of AD patients and healthy subjects' serum using the Surface Enhanced Raman Spectroscopy (SERS), taking into consideration the effect of different variables on the final spectra, analyzed and compared through multivariate analysis and correlated with hippocampus volume. As results, we demonstrated a statistical difference between the spectra collected from the two investigated groups, with an accuracy, precision and specificity of respectively 83%, 86%, and 86%. The correlation of these data with those obtained from MRI, demonstrated a direct correlation between Raman spectra and hippocampus degeneration showing the Raman Spectroscopy (RS) as a potential tool for the monitoring of AD progression and rehabilitation treatments.     

Large-Scale Purification of Porcine or Bovine Photoreceptor Outer Segments for Phagocytosis Assays on Retinal Pigment Epithelial Cells

Analysis of one of the vital functions of retinal pigment epithelial (RPE) cells, the phagocytosis of spent aged distal fragments of photoreceptor outer segments (POS) can be performed in vitro. Photoreceptor outer segments with stacks of membranous discs containing the phototransduction machinery are continuously renewed in the retina. Spent POS are eliminated daily by RPE cells. Rodent, porcine/bovine and human RPE cells recognize POS from various species in a similar manner. To facilitate performing large series of experiments with little variability, a large stock of POS can be isolated from porcine eyes and stored frozen in aliquots. This protocol takes advantage of the characteristic of photopigments that display an orange color when kept in the dark. Under dim red light, retinae are collected in a buffer from opened eyecups cut in halves. The retinal cell suspension is homogenized, filtered and loaded onto a continuous sucrose gradient. After centrifugation, POS are located in a discrete band in the upper part of the gradient that has a characteristic orange color. POS are then collected, spun, resuspended sequentially in wash buffers, counted and aliquoted. POS obtained this way can be used for phagocytosis assays and analysis of protein activation, localization or interaction at various times after POS challenge. Alternatively, POS can be labeled with fluorophores, e.g., FITC, before aliquoting for subsequent fluorescence quantification of POS binding or engulfment. Other possible applications include the use of modified POS or POS challenge combined with stress conditions to study the effect of oxidative stress or aging on RPE cells.