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At least 595 records · Page 33Linked to original sources
PubMed2002

SPA1, a component of phytochrome A signal transduction, regulates the light signaling current.

Mutations in a component of phytochrome A (phyA)-specific light signal transduction, SPA1, result in enhanced responsiveness of Arabidopsis seedlings to red and far-red light. Here, we have examined the effects of spa1 mutations on the two known modes of phyA function, the high-irradiance responses (HIRs) to continuous irradiation with far-red light and the very-low-fluence responses (VLFRs) to inductive pulses of light that establish only a small proportion of active phyA. spa1 mutants exhibited an enhanced VLFR under hourly pulses of far-red light for hypocotyl growth inhibition, cotyledon unfolding, anthocyanin accumulation, block of greening in subsequent white light and negative regulation of phyB signaling. We provide evidence that the phenotype of spa1 mutants in red light is also caused by an increase in the VLFR. Taken together, our results indicate that light-induced hypocotyl growth inhibition in spa1 mutants is primarily due to a VLFR. While wild-type seedlings required hourly pulses of far-red light to induce a VLFR, infrequent irradiation with far-red pulses (every 12 h) was sufficient to induce a strong VLFR of hypocotyl elongation in spa1 mutants. This shows that the effect of the VLFR was more persistent in spa1 mutants than in the wild type. We, therefore, propose that SPA1 has an important function in reducing the persistence of phyA signaling. spa1 mutations also enhanced the HIRs of anthocyanin accumulation and of phyA-mediated responsivity amplification towards phyB. Thus, our results suggest that spa1 mutations amplify both the phyA-mediated VLFR and the HIR.

Anthocyanins↗
PubMed1995

Evaluation of cell death in EBV-transformed lymphocytes using agarose gel electrophoresis, light microscopy and electron microscopy. I. Induction of classic apoptosis by the bile salt, sodium deoxycholate.

In this study, we examined the effect of different concentrations of sodium deoxycholate (NaDOC), a secondary bile salt, on an Epstein-Barr virus transformed human lymphoid cell line (NC-37). We found that NaDOC induces classic apoptosis in a dose-dependent manner at 0.1-0.4 mM doses, and necrosis at much higher concentrations (0.8-3.1 mM). This is the first demonstration that a bile salt can induce apoptosis in any cell type. The mode of cell death was determined using morphologic methods (light and electron microscopy) as the gold standard. Standard agarose gel electrophoretic techniques were applied to identify the "ladder" of DNA fragments that have been associated with apoptosis in certain cell types. Although DNA fragmentation was observed during the apoptotic death of NC-37 cells, we were not able to identify a "ladder" pattern of fragmentation. Two other types of cells, however, that previously have been reported to display a characteristic "ladder" pattern of DNA fragmentation, glucocorticoid-treated WEHI7.2 cells and isolated human neutrophils, did display the "ladder" pattern. This study emphasizes the need to examine morphology when identifying the mode of cell death induced by a new agent.

Apoptosis↗
PubMed2004

Enhancement of cyclic electron flow around PSI at high light and its contribution to the induction of non-photochemical quenching of chl fluorescence in intact leaves of tobacco plants.

Non-photochemical quenching (NPQ) of Chl fluorescence is a mechanism for dissipating excess photon energy and is dependent on the formation of a DeltapH across the thylakoid membranes. The role of cyclic electron flow around photosystem I (PSI) (CEF-PSI) in the formation of this DeltapH was elucidated by studying the relationships between O2-evolution rate [V(O2)], quantum yield of both PSII and PSI [Phi(PSII) and Phi(PSI)], and Chl fluorescence parameters measured simultaneously in intact leaves of tobacco plants in CO2-saturated air. Although increases in light intensity raised V(O2) and the relative electron fluxes through both PSII and PSI [Phi(PSII) x PFD and Phi(PSI) x PFD] only Phi(PSI) x PFD continued to increase after V(O2) and Phi(PSII) x PFD became light saturated. These results revealed the activity of an electron transport reaction in PSI not related to photosynthetic linear electron flow (LEF), namely CEF-PSI. NPQ of Chl fluorescence drastically increased after Phi(PSII) x PFD became light saturated and the values of NPQ correlated positively with the relative activity of CEF-PSI. At low temperatures, the light-saturation point of Phi(PSII) x PFD was lower than that of Phi(PSI) x PFD and NPQ was high. On the other hand, at high temperatures, the light-dependence curves of Phi(PSII) x PFD and Phi(PSI) x PFD corresponded completely and NPQ was not induced. These results indicate that limitation of LEF induced CEF-PSI, which, in turn, helped to dissipate excess photon energy by driving NPQ of Chl fluorescence.

Chlorophyll↗
PubMed1997

Light-induced resetting of a mammalian circadian clock is associated with rapid induction of the mPer1 transcript.

To understand how light might entrain a mammalian circadian clock, we examined the effects of light on mPer1, a sequence homolog of Drosophila per, that exhibits robust rhythmic expression in the SCN. mPer1 is rapidly induced by short duration exposure to light at levels sufficient to reset the clock, and dose-response curves reveal that mPer1 induction shows both reciprocity and a strong correlation with phase shifting of the overt rhythm. Thus, in both the phasing of dark expression and the response to light mPer1 is most similar to the Neurospora clock gene frq. Within the SCN there appears to be localization of the induction phenomenon, consistent with the localization of both light-sensitive and light-insensitive oscillators in this circadian center.

Animals↗
PubMed2000

Heterodimeric amino acid transporters: expression of heavy but not light chains of CD98 correlates with induction of amino acid transport systems in human placental trophoblast.

1. Activity of amino acid transport and relative abundance of mRNAs encoding related transporters have been studied in parallel either before or following in vitro culture of explants of human placental chorionic villi. 2. Amino acid transport activities through systems L (1.9-fold), y+L (2.6-fold) and y+ (3.2-fold) were markedly enhanced following culture for 48 h. 3. Relative mRNA abundance (determined by reverse transcription-polymerase chain reaction) for the heavy chain of CD98 surface antigen and for the cationic amino acid transporter-1 were similarly stimulated (2.8-fold and 2.6-fold, respectively). In contrast, none of the mRNA levels for light chains of CD98 (system L-amino acid transporter-1, system L-amino acid transporter-2, system y+L-amino acid transporter-1 and system y+L-amino acid transporter-2) studied nor for the cationic amino acid transporter-2B were altered.

Amino Acid Transport Systems↗
PubMed1990

Photosynthetic induction state of leaves in a soybean canopy in relation to light regulation of ribulose-1-5-bisphosphate carboxylase and stomatal conductance.

Photosynthetic induction state, stomatal conductance and light regulation of ribulose-1,5-bisphosphate carboxylase (rubisco) were examined for leaves in a mature, closed soybean (Glycine max) canopy (leaf area index approximately 5) with the objective to determine the extent to which these factors may be limiting the capacity to respond to light transients during sunflecks. When sampled along a vertical gradient, leaves near the bottom of the canopy had lower rubisco contents and chlorophyll a/b ratios as compared with upper leaves. Leaves sampled at midcanopy showed a wide variation in photosynthetic induction state (ratio of the photosynthetic rate achieved after 1 minute exposure to high light to the steady-state assimilation rate achieved after 20 minutes exposure). Both photosynthetic induction state and the initial rubisco activity varied in parallel with stomatal conductance. By contrast there was no correlation between total rubisco activity and stomatal conductance. The results indicate that induction state, as determined by the light regulation of both rubisco activity and stomatal conductance, is an important limitation to the ability of leaves in a soybean canopy to respond to light transients that occur during sunflecks.

Journal Article↗
PubMed1995

Evaluation of cell death in EBV-transformed lymphocytes using agarose gel electrophoresis, light microscopy and electron microscopy. II. Induction of non-classic apoptosis ("para-apoptosis") by tritiated thymidine.

There is an extensive literature dating back to the late 1950's, on the damaging biological effects of radiolabeling DNA in vivo. Nonetheless, tritiated thymidine has often been used to label DNA in studies of programmed cell death (apoptosis). In the present study, we have investigated the effects of incorporation of tritiated thymidine into the DNA of an Epstein-Barr virus-transformed cell line (NC-37) in the absence of any other apoptosis-inducing agent. Cells were incubated in media containing 1-20 microCi/ml [methyl-3H]-thymidine ([3H]-TdR). At each concentration of tritiated thymidine used, cell proliferation ceased within 12 hours of incubation. The mode of cell death caused by tritiated thymidine incorporation was evaluated using DNA degradation patterns and cellular morphology. DNA degradation, in the absence of a "ladder" pattern, was shown by agarose gel electrophoresis. Electron microscopy was used as the "gold standard" to evaluate the specific morphologic type of cell death that accompanied the DNA degradation. Although some of the features of apoptosis were present, the cells lacked the early margination of the chromatin within an intact nucleus and surface blebbing leading to apoptotic body formation, two characteristic morphological features of apoptosis. We, therefore, coined the term "para-apoptosis" to be more precise about the morphologic type of cell death. The percent of para-apoptotic cells was quantitated by light microscopy using whole mount preparations (cytospins). The morphologic criteria of chromatin condensation, nuclear fragmentation, increase in cell density and cytoplasmic vacuolization were used for the evaluation of para-apoptosis by light microscopy of cytospin preparations. In the absence of tritiated thymidine, < 2% of the cells became apoptotic/para-apoptotic after 43 hours of incubation. However, at all concentrations of tritiated thymidine used in the incubation medium (1-20 microCi/ml), the number of para-apoptotic cells increased. In addition, we detected perturbations in the timing of the cell cycle of the surviving cells and an increase in the number of micronuclei after only one division cycle. The induction of para-apoptosis and micronuclei formation represent two distinct modes of cell death caused by tritiated thymidine incorporation. These studies emphasize the necessity for morphological examination in characterizing the induction of cell death in a new experimental system.

Apoptosis↗
PubMed1990

Induction of Shikimic Acid Pathway Enzymes by Light in Suspension Cultured Cells of Parsley (Petroselinum crispum).

Light treatment of suspension cultured cells of parsley (Petroselinum crispum) was shown to increase the activity of the shikimic acid pathway enzyme, 3-deoxy-d-arabino-heptulosonic acid-7-phosphate (DAHP) synthase (EC 4.1.2.15). DAHP synthase activity was assayed for two isoforms, DS-Mn and DS-Co (RJ Ganson, TA d'Amato, RA Jensen [1986] Plant Physiol 82: 203-210). Light increased the enzymatic activity of the plastidic isoform DS-Mn as much as 2-fold, averaging 1.6-fold with >95% confidence. The cytosolic isoform DS-Co was unaffected. Cycloheximide and actinomycin D, translational and transcriptional inhibitors, respectively, both reversed induction of DS-Mn by light suggesting transcriptional regulation of the gene. Chorismate mutase activity was assayed for the two isoforms CM I and CM II (BK Singh, JA Connelly, EE Conn [1985] Arch Biochem Biophys 243: 374-384). Treatment by light did not significantly affect either chorismate mutase isoform. The ratio of the two chorismate mutase isoforms changed during the growth cycle, with an increase in the ratio of plastidic to cytosolic isoforms occurring towards the end of logarithmic growth.

Journal Article↗
PubMed1994

Regulation of heme oxygenase activity in Cyanidium caldarium by light, glucose, and phycobilin precursors.

Cyanobacteria, red algae, and cryptophytes contain phycobiliproteins which function as photosynthetic light-harvesting pigments. The chromophores of phycobiliproteins are phycobilins, open-chain tetrapyrroles that are synthesized from protoheme. The first step of phycobilin formation is the conversion of protoheme to biliverdin IX alpha in a reaction that is catalyzed by heme oxygenase. In the unicellular red alga, Cyanidium caldarium, light is required for the accumulation of phycobiliproteins. It has been reported previously that the synthesis of the apoprotein components of allophycocyanin and phycocyanin is induced by light in C. caldarium, that the phycobilin precursors, delta-aminolevulinic acid (ALA), protoporphyrin IX, and protoheme can substitute for light, and that the regulation is exerted at the level of mRNA synthesis. We have determined that a key enzyme of phycobilin formation is induced by light in C. caldarium. Extractable heme oxygenase activity is low in dark-grown cells, and it increases approximately 6-fold during the first 24 h after the cells are illuminated. After 24 h, the activity decreases to a level approximately equal to the initial activity. Heme oxygenase is induced in unilluminated cells by administration of ALA. D-Glucose, which is known to inhibit phycocyanin accumulation in C. caldarium, inhibits the induction of heme oxygenase by light or ALA. Induction of heme oxygenase by light or ALA is blocked by cycloheximide, an inhibitor of cytoplasmic protein synthesis, but not by chloramphenicol, an inhibitor of chloroplast protein synthesis. Rifampicin, an inhibitor of algal chloroplast RNA synthesis, and gabaculine, a competitive inhibitor of ALA biosynthesis, block the induction of heme oxygenase by light but not by ALA. These results indicate that heme oxygenase in C. caldarium is induced by phycobilin precursors. The induction by light and the repression of the induction by D-glucose are probably indirect effects mediated by the effects of light and D-glucose on phycobilin precursor formation. The results also indicate that heme oxygenase is encoded by a nuclear gene and is synthesized on cytoplasmic ribosomes.

Aminolevulinic Acid↗
PubMed1985

Ultraviolet radiation-induced histopathologic changes in the skin of the marsupial Monodelphis domestica. II. Quantitative studies of the photoreactivation of induced hyperplasia and sunburn cell formation.

Induction of sunburn cells (SBCs) and hyperplasia of the epidermis of the marsupial Monodelphis domestica by ultraviolet radiation (UVR) has been studied. A dose of 500 J/m2 (approximately 1 minimal erythemal dose) from an FS-40 sunlamp induced measurable numbers of SBCs with a peak number at 32-48 h post-UVR exposure of skin to photoreactivating light suppressed the induction of SBCs by approximately 75%. Pre-UVR exposure to photoreactivating light had no effect on the induction of SBCs. Induction of hyperplasia also was suppressed to a similar extent by post-UVR photoreactivation treatment. These studies identify pyrimidine dimers in DNA as the major photoproduct involved in the induction of SBCs and hyperplasia in M. domestica by UVR.

Animals↗
PubMed1982

Induction of chromosome damage by ultraviolet light and caffeine: correlation of cytogenetic evaluation and flow karyotype.

Asynchronously growing cells of a M3-1 Chinese hamster line were ultraviolet (UV) irradiated (lambda = 254 nm) with UV fluences up to 7.5 J/m(2). After irradiation cells were incubated with or without 2 mM caffeine for 20 hr, then mitotic cells were selected by mechanical shaking. Their chromosomes were isolated, stained with Hoechst 33258 and chromomycin A3, and measured flow cytometrically. While the fluorescence distributions of chromosomes (flow karyo-types) from cells treated with UV alone or with caffeine alone were very similar to those of untreated controls, the flow karyo-types of UV + caffeine-treated cells showed a debris continuum that increased with increasing UV fluence suggesting an increased number of chromosome fragments. Visual evaluation of metaphase plates revealed that the percentage of cells with chromosome damage also increased steadily with increasing UV fluence. A high degree of correlation was observed between the relative magnitude of the debris level from flow karyotypes and the percentage of cells with chromosome damage and with generalized chromosomes shattering, respectively, as determined from metaphase spreads.

Animals↗
PubMed1984

Selective and polyclonal induction of high levels of lambda light chain-bearing immunoglobulins in BALB/c and SJL mice.

Polyclonal B cell activation is V gene independent and consequently results in the unselected expression of both V lambda and V kappa genes. In an attempt to selectively and polyclonally trigger lambda light chain-bearing B cells, we immunized mice with low doses of lipopolysaccharide (LPS) coupled to antibodies specific for the constant region of lambda 1 chains. Analyses of the sera of treated mice revealed that LPS anti-lambda 1 selectively triggers lambda-but not kappa-bearing B cells to high rate Ig secretion. Surprisingly, immunized SJL mice (rlo lambda 1 phenotype) mounted a lambda + response comparable to that detected in mice with the r + lambda 1 phenotype. Because we could definitively establish that the majority of the induced antibodies belong the lambda 1 subtype, our results have strong implications both for the study of the repertoire of lambda 1-bearing B cells and for our understanding of the functional mechanism(s) by which the r lambda 1 locus acts.

Animals↗
PubMed1978

Stimulation of host DNA synthesis and induction of early antigens by ultraviolet light irradiated human cytomegalovirus.

The ultraviolet (UV-)sensitivity of the human cytomegalovirus (HCMV) genes coding for very early complement fixing and early antigens in human embryonic fibroblasts (HEF) and mouse embryonic fibroblasts (MEF) and the relation of these genes to the ability of the virus to stimulate host cell DNA synthesis were investigated. After 14 minutes of UV-irradiation of the virus inoculum only the very early complement fixing nuclear antigen (CMNA) developed in the HEF cells and only the early cytoplasmic antigen(s) was present in the MEF. In both HEF and MEF, host cell DNA synthesis was stimulated. We conclude that the ability of HCMV to stimulate host DNA synthesis is an early function of the viral genome and shows a high resistance to UV-irradiation. There is no direct correlation, however, between the ability of the virus to stimulate host cell DNA synthesis and the genes which code for the CMNA or for early cytoplasmic antigens.

Antigens, Viral↗
PubMed1980

Increased sensitivity of cell strains from Cockayne's syndrome to sister-chromatid-exchange induction and cell killing by UV light.

Ultraviolet light-induced sister-chromatid exchanges (SCE) and cell killing were investigated in 4 fibroblast cell strains from patients with the sun-sensitive disease Cockayne's syndrome (CS). All 4 CS cell strains proved to be hypersensitive to UV for both of these end-points, but no close correlation between levels of SCE and lethality was observed. Cell strains from two individuals heterozygous for CS were indistinguishable from wild-type.

Cell Survival↗
PubMed1986

Induction of chromosome shattering by ultraviolet light and caffeine: the influence of different distributions of photolesions.

Cells of synchronized and of asynchronously growing cultures of a V79 Chinese hamster line were microirradiated with a low power laser-UV-microbeam of wavelength 257 nm. Ultraviolet light was either focused onto a small part of the nucleus (mode I) or distributed over the whole nucleus (mode II). Following microirradiation, the cells were incubated for 7-20 h with caffeine (1-2 mM) until chromosome preparation was performed. After both modes of microirradiation, shattering of the entire chromosome complement (generalized chromosome shattering, GCS) was observed. It is suggested that the probability by which GCS is induced depends on the total number of DNA lesions rather than on their distribution in the chromatin. The results are consistent with the prediction of a "factor depletion model" which assumes that in a given cell, GCS takes place both in irradiated and non-irradiated chromosomes if the total number of daughter strand-repair sites surpasses a threshold value.

Animals↗