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At least 991 records · Page 55Linked to original sources
PubMed1994

Blue light sensory systems in plants.

Plant development is influenced by many environmental stimuli, including light, temperature and gravity. Of these stimuli, light is of particular importance because plants depend on it for energy and, thus, for survival. Moreover, virtually all stages of plant development are regulated in part by light through the action of various photosensory systems. Examples of light-regulated processes include germination, stem growth, leaf and root development, tropic responses and flower induction. This review provides an analysis of recent investigations of blue light sensory systems in plants. Current results suggest that plants respond to blue light through a complex photosensory network that incorporates the action of multiple blue light perception systems.

Light↗
PubMed1992

Calcium is necessary for light excitation in barnacle photoreceptors.

Illumination of barnacle (Balanus amphitrite) photoreceptors is known to increase the membrane permeability to sodium and Ca2+ ions resulting in a depolarizing receptor potential. In this report, we show that lanthanum (La3+), a known inhibitor of Ca-binding proteins, reversibly eliminates the receptor potential of barnacle photoreceptors when applied to the extracellular space. Similar reversible elimination of the light response was obtained by removing extracellular Ca2+ by application of the calcium chelating agent EGTA. Iontophoretic injection of Ca2+, but not K+ into the cells protected both the transient and the steady-state phases of the receptor potential from elimination by EGTA while only the transient phase was protected in the presence of La3+. The EGTA experiments suggest that internal Ca2+ is necessary for light excitation of barnacle photoreceptors while the La3+ experiments suggest that La(3+)-sensitive inward current is necessary to maintain excitation during prolonged light.

Animals↗
PubMed1996

Role of Drosophila TRP in inositide-mediated Ca2+ entry.

Inositol lipid signaling relies on an InsP3-induced Ca2+ release from intracellular stores and on extracellular Ca2+ entry, which takes place when the Ca2+ stores become depleted of Ca2+. This interplay between Ca2+ release and Ca2+ entry has been termed capacitative Ca2+ entry and the inward current calcium release activated current (CRAC) to indicate gating of Ca2+ entry by Ca2+-store depletion. The signaling pathway and the gating mechanism of capacitative Ca2+ entry, however, are largely unknown and the molecular participants in this process have not been identified. In this article we review genetic, molecular, and functional studies of wild-type and mutant Drosophila photoreceptors, suggesting that the transient receptor potential mutant (trp) is the first putative capacitative Ca2+ entry mutant. Furthermore, several lines of evidence suggest that the trp gene product TRP is a candidate subunit of the plasma membrane channel that is activated by Ca2+ store depletion.

Animals↗
PubMed1992

Light does not induce an increase in cyclic-GMP content of squid or Limulus photoreceptors.

Both slices of squid (Loligo) retinas and Limulus ventral photoreceptors, with or without prior stimulation by flashes of bright light, were rapidly frozen and analysed for cyclic-GMP content by radioimmunoassay. Measurement of the freezing process indicated that freezing occurred at about 100 msec after the light flash. No significant changes in cyclic-GMP content were induced by light in either tissue. These data do not confirm previous reports that cyclic-GMP content of invertebrate photoreceptors is markedly increased by illumination.

Animals↗
PubMed2006

Integrative analysis of transcript and metabolite profiling data sets to evaluate the regulation of biochemical pathways during photomorphogenesis.

One of the key developmental processes during photomorphogenesis is the differentiation of prolamellar bodies of proplastids into thylakoid membranes containing the photosynthetic pigment-protein complexes of chloroplasts. To study the regulatory events controlling pigment-protein complex assembly, including the biosynthesis of metabolic precursors and pigment end products, etiolated Arabidopsis thaliana seedlings were irradiated with continuous red light (Rc), which led to rapid greening, or continuous far-red light (FRc), which did not result in visible greening, and subjected to analysis by oligonucleotide microarrays and targeted metabolite profiling. An analysis using BioPathAt, a bioinformatic tool that allows the visualization of post-genomic data sets directly on biochemical pathway maps, indicated that in Rc-treated seedlings mRNA expression and metabolite patterns were tightly correlated (e.g., Calvin cycle, biosynthesis of chlorophylls, carotenoids, isoprenoid quinones, thylakoid lipids, sterols, and amino acids). K-means clustering revealed that gene expression patterns across various biochemical pathways were very similar in Rc- and FRc-treated seedlings (despite the visible phenotypic differences), whereas a principal component analysis of metabolite pools allowed a clear distinction between both treatments (in accordance with the visible phenotype). Our results illustrate the general importance of integrative approaches to correlate post-genomic data sets with phenotypic outcomes.

Arabidopsis↗
PubMed2004

Cryptochromes: tail-ored for distinct functions.

Cryptochromes are important components of circadian clocks in both plants and animals. Recent work suggests that the carboxy-terminal tails of these conserved proteins are used in drastically different ways in different organisms.

Biological Clocks↗
PubMed2006

Phototropin and light-signaling in phototropism.

Blue-light-induced phototropism in higher plants is regulated by phototropin, which is a photoreceptor kinase that contains a flavin mononucleotide (FMN). Recently, it was found that this kinase is inhibited by the binding of the LOV2 (light-oxygen-voltage2) domain in the dark but that its activity is increased in the light by the release of the LOV2 domain. Phototropin-associated proteins have been identified, although the proteins that are phosphorylated by phototropin are still unknown. The asymmetrical auxin distribution caused by unilateral irradiation suggests that differential growth is induced by a difference in auxin-regulated gene expression between the shaded and illuminated sides of plant organs. Transcription-related factors, such as NPH4/ARF7, MSG2/IAA19 and SCF(TIR1), play key roles in this process.

Cryptochromes↗
PubMed2006

Powered by pairing: the surrogate light chain amplifies immunoglobulin heavy chain signaling and pre-selects the antibody repertoire.

Selective expansion of functional pre-B cells is accomplished by the assembly of a signaling-competent pre-B cell receptor (pre-BCR) consisting of immunoglobulin mu heavy chains (muHC), surrogate light chains (SLC) and Igalpha/Igbeta. Here, we review recent data showing that muHCs, in the absence of SLC, deliver autonomous differentiation signals. However, enhanced signaling necessary for pre-B cell expansion requires cross-linking of pre-BCRs via the non-immunoglobulin tail of SLC's subunit lambda5. We also discuss how SLC's ability to modulate the strength of pre-BCR signals is controlled by a muHC's idiotype and its affinity to the chaperone BiP. In this model, BiP in concert with SLC functions as a pre-selector of the antibody repertoire.

Animals↗
PubMed2005

Cereal phytochromes: targets of selection, targets for manipulation?

Plants respond to shading through an adaptive syndrome termed shade avoidance. In high-density crop plantings, shade avoidance generally increases extension growth at the expense of yield and can be at odds with the agronomic performance of the crop as a whole. Studies in Arabidopsis are beginning to reveal the essential role phytochromes play in regulating this process and to identify genes underlying the response. In this article, we focus on how phytochrome signaling networks have been targeted in cereal breeding programs in the past and discuss the potential to alter these pathways through breeding and transgenic manipulation to develop crops that perform better under typical high density conditions.

Edible Grain↗
PubMed1990

All-trans/13-cis isomerization of retinal is required for phototaxis signaling by sensory rhodopsins in Halobacterium halobium.

An analogue of all-trans retinal in which all-trans/13-cis isomerization is blocked by a carbon bridge from C12 to C14 was incorporated into the apoproteins of sensory rhodopsin I (SR-I) and sensory rhodopsin II (SR-II, also called phoborhodopsin) in retinal-deficient Halobacterium halobium membranes. The "all-trans-locked" retinal analogue forms SR-I and SR-II analogue pigments with similar absorption spectra as the native pigments. Blocking isomerization prevents the formation of the long-lived intermediate of the SR-I photocycle (S373) and those of the SR-II photocycle (S-II360 and S-II530). A computerized cell tracking and motion analysis system capable of detecting 2% of native pigment activity was used for assessing motility behavior. Introduction of the locked analogue into SR-I or SR-II apoprotein in vivo did not restore phototactic responses through any of the three known photosensory systems (SR-I attractant, SR-I repellent, or SR-II repellent). We conclude that unlike the phototaxis receptor of Chlamydomonas reinhardtii, which has been reported to mediate physiological responses without specific double-bond isomerization of its retinal chromophore (Foster et al., 1989), all-trans/13-cis isomerization is essential for SR-I and SR-II phototaxis signaling.

Archaeal Proteins↗
PubMed2006

[Role and regulation of dopamine D1 receptors in the striatum: implications for the genesis of dyskinesia in Parkinson's disease].

L-dopa treatment of Parkinson's disease is complicated in the long term by the appearance of dyskinesia. Hypersensitivity of D1 dopamine receptor has been suggested to play a role in these delayed adverse effects. Hypersensitivity of dopamine D1 receptor in Parkinson's disease can be accounted for by increased levels of Galphaolf, the stimulatory G protein which couples D1 receptor to adenylyl cyclase in the striatum. We here discuss the possible role of D1 receptor signal transduction in the genesis of L-dopa-induced dyskinesia in the light of Galphaolf regulation.

Antiparkinson Agents↗
PubMed1992

The role of cytoplasmic calcium in photoreceptor light adaptation.

The process of light adaptation in vertebrate rod and cone photoreceptors is believed to involve a diffusible cytoplasmic messenger. Two lines of evidence indicate that photoreceptor light adaptation is mediated by a light-induced fall in cytoplasmic calcium concentration (Ca2+i). First, if changes in calcium concentration are slowed by the incorporation of calcium chelators into the photoreceptor cytoplasm then light adaptation is slowed also. Second, if the normal control of Ca2+i is prevented by simultaneously minimising calcium influx and efflux across the outer segment membrane by means of external solution changes, then all of the manifestations of light adaptation are abolished. Furthermore, recent results show that changes in Ca2+i imposed in the absence of light are sufficient to cause at least some of the manifestations of light adaptation. Together these results indicate that calcium acts as the messenger of light adaptation in the photoreceptors of both lower and higher vertebrates.

Adaptation, Physiological↗
PubMed2001

Pathways of plastid-to-nucleus signaling.

Several plastid signals have been identified that regulate the transcription of nuclear genes for plastid and non-plastid proteins. These signals are related to the photosynthetic metabolism of chloroplasts and include porphyrins, reactive oxygen intermediates and carotenoids. The metabolic and developmental state of the chloroplast also control cell differentiation and leaf morphogenesis, but the signaling pathways have not been characterized. Plastid-to-nucleus and light-signaling pathways are separable in some but not all cases. Retrograde signaling thus plays a central role in coordinating gene expression in the nucleus, plastid and mitochondrion, and in integrating pathways of cellular metabolism and development.

Cell Nucleus↗
PubMed1992

ATP-independent deactivation of squid rhodopsin.

Deactivation of light-activated squid rhodopsin was studied in vitro using GTP gamma S binding by G-protein as a direct measure of rhodopsin activity. Deactivation was inhibited by dilution of the retinal suspension or by removal of soluble components. Deactivation could be restored by addition of soluble material to washed membranes. These results indicate that the deactivation is not due entirely to a conformational transition within rhodopsin itself, but depends on the interaction with other molecules. The possibility that phosphorylation is involved in the deactivation was studied. Deactivation occurred in the presence and absence of added ATP. Deactivation also occurred in the presence of kinase inhibitors and after addition of apyrase, which reduced residual ATP levels to below 1 microM. These results indicate that light-induced phosphorylation is not required for deactivation of squid rhodopsin. In this regard deactivation of squid rhodopsin is different from that of vertebrate rhodopsin, which requires phosphorylation.

Adenosine Triphosphate↗
PubMed1991

Mechanisms of early visual processing in the medulla of the locust optic lobe: how self-inhibition, spatial-pooling, and signal rectification contribute to the properties of transient cells.

In the arthropod medulla, which is the second ganglion on the afferent visual pathway, a column of about 40 cells represents each point in space (i.e. compound eye facet). Some stages of visual processing underlying the responses of one class of cells in the locust medulla have been identified. These transient cells give very similar responses to intensity increments and decrements, and also to pulses and steps; there is no spontaneous activity and a stimulus causes one or two spikes to fire at fixed latencies. Movement, however, produces a prolonged spike discharge by successive excitation of subunits within the receptive field. One of the main features of the transient cells' responses is a self-inhibition which attenuates responses to successive stimuli at one point. This inhibition is restricted to the outputs of single receptor (rhabdom), it decays after about 100 ms, and is polarity sensitive so that stimuli of one polarity (e.g. dimming) do not inhibit responses to stimuli of the opposite polarity (e.g. brightening). The inhibition effectively alters the contrast threshold of the cells, because after adaptation with stimuli of one contrast, a modest (less than 20%) increase in contrast is sufficient to elicit an unadapted response. Transient cells are not directionally selective and there are no local spatio-temporal interactions of the kind necessary for directional selectivity. But, by analogy with the directional veto in directionally selective cells in the rabbit retina (Barlow & Levick, 1965), self-inhibition is suggested as a mechanism of non-directional motion detection. After the inhibition, there is some spatial pooling of signals which is followed by rectification. The transient cells' spiking outputs could abstract a refined subset of visual information which may encode the presence, but not the direction, amplitude, or polarity of moving object borders.

Afferent Pathways↗
PubMed1992

Electrophysiological recordings in solitary photoreceptors from the retina of squid, Loligo pealei.

A protocol was developed to isolate enzymatically photoreceptors from the retina of the squid, Loligo pealei. The procedure routinely results in a high yield of intact cells. Examination of solitary photoreceptors under Nomarski optics revealed that the fine morphological features described in anatomical studies of retinal sections are retained. The distal segment is up to 250 microns long, 4-7 microns wide, covered in part by short microvilli; the inner segment and the cell body, with the initial portion of the axon, are also clearly discernible in solitary cells. Suction electrode measurements performed from the cell body confirmed that responsiveness to light survived cell isolation. Macroscopic membrane currents were measured using the whole-cell tight-seal technique, and the perforated-patch method. Step depolarizations of membrane voltage administered in the dark elicited a slowly activating, sustained outward current. Light stimulation evoked an inward current graded with stimulus intensity; the peak current could amply exceed 1000 pA. Intense photostimulation gave rise to a prolonged inward aftercurrent that lasted for tens of seconds. On-cell patch recording along the intermediate segment and most of the smooth areas of the distal segment showed a large incidence of silent patches, with the occasional presence of voltage-dependent channels. On the other hand, channel activity could be recorded more frequently from electrode placements near the apical tip of the cell, where the presence of microvilli could be confirmed visually. Some patches were unresponsive to voltage stimulation applied in the dark but produced distinct bursts of channel openings after illumination. The feasibility of single-cell electrophysiology in isolated photoreceptors, together with the growing body of biochemical information on cephalopod preparations, makes squid an attractive model system to investigate the visual process in invertebrates using multiple experimental approaches.

Animals↗
PubMedDate not supplied

Steady discharges of macaque retinal ganglion cells.

Steady discharges were collected from ganglion cells of the magnocellular (MC) and parvocellular (PC) pathways of the macaque while their receptive fields were uniformly illuminated with a 4.7-deg steady yellow light of photopic illuminance. The mean rates, coefficients of variation, interval distributions, serial correlation coefficients, and power spectra of these discharges were determined. The results presented permit one to estimate the noise power in the discharges of macaque ganglion cells and hence determine how visual signals of different amplitudes will be affected by the noise resident in their discharges. Although there was some small serial correlation in the discharges of both MC- and PC-pathway cells, their discharges can be considered to result from renewal processes with reasonable accuracy. As with the discharges of cat ganglion cells, macaque ganglion cell discharges can be considered to have approximately gamma-distributed intervals. Steady discharges of MC- and PC-pathway cells show considerable overlap in their statistics, although small but significant differences are present.

Action Potentials↗