Seed germination of Hesperozygis ringens (Benth. ) Epling, an endemic and threatened species

Hesperozygis ringens (Lamiaceae), popularly known as espanta-pulga, is a threatened species endemic to rocky and sandy regions of the Pampa biome. One factor that can influence the low number of individuals of a species is a low seed germination rate influenced by temperature and/or light. Thus, the objective of this study was to evaluate the influence of light and temperature on the seed germination of H. ringens. The seeds of two lots were sown on a paper substrate and maintained in BOD chambers at temperatures of 15, 20, 25 and 30ºC in the presence and absence of light. The germination speed rate was evaluated every 3 days for 21 days. The experiment was completely randomized with treatments that had a 4 x 2 factorial design. The first visible sign (protrusion of the primary root) of germination was observed seven days after sowing. Germination occurred both in the presence and absence of light and the lowest temperatures significantly influenced the germination process and germination speed. For germinating the species, 15°C was the most favorable temperature compared to 20, 25 and 30°C. It can be concluded that a temperature of 15ºC favors the germination process of H. ringens seeds, which are insensitive to light.(AU)

Photoperiodic regulation of seasonal reproduction in higher vertebrates.

Long-lived animals such as birds and mammals adapt readily to seasonal changes in their environment. They integrate environmental cues with their internal clocks to prepare and time seasonal physiological changes. This is reflected in several seasonal phenotypes, particularly in those linked with migration, hibernation, pelage growth, reproduction and molt. The two endocrine secretions that play key roles in regulating the seasonal physiology are melatonin and thyroid hormone. Whereas, melatonin is used as an endocrine index of day length (and consequently duration of night), the seasonal up- and down-regulation of thyroid hormone affects the physiology, perhaps by influencing different pathways. Both of these hormones are shown to act via a ‘photoperiodic axis’ constituted by the photoreceptors, hypothalamus and pituitary. Recent studies have revealed that the pars tuberalis that connects hypothalamus and pituitary, locally synthesizes the thyroid stimulating hormone (TSH) in response to light (birds) or melatonin (mammals). The levels of TSH regulate the DIO2 and DIO3 synthesis in the ependymal cells in hypothalamus, and in turn affect the release of gonadotropin releasing hormone. This review mainly focuses on the current understanding of the mechanisms of photoperiodic regulation of seasonal responses in the higher vertebrates.

Fatty acid composition of Drosophila photoreceptor light-sensitive microvilli

Phototransduction, the mechanism underlying the electrical response to light in photoreceptor cells, has been thoroughly investigated in Drosophila melanogaster, an essential model in signal transduction research. These cells present a highly specialized photosensitive membrane consisting of thousands of microvilli forming a prominent structure termed a rhabdomere. These microvilli encompass the phototransduction proteins, most of which are transmembrane and exclusively rhabdomeric. Rhabdomere membrane lipids play a crucial role in the activation of the transient receptor potential ionic channels (TRP and TRPL) responsible for initiating the photoresponse. Despite its importance, rhabdomere lipid composition has not been established. We developed a novel preparation enriched in rhabdomere membranes to perform a thorough characterization of the lipidomics of Drosophila rhabdomeres. Isolated eyes (500) were homogenized and subjected to a differential centrifugation protocol that generates a fraction enriched in rhabdomere membrane. Lipids extracted from this preparation were identified and quantified by gas chromatography coupled to mass spectrometry. We found an abundance of low sterol esters (C16:0, C18:0), highly abundant and diverse triglycerides, free fatty acids, a moderate variety of mono and diacyglycerols (C:16:0, 18:0, C18:1) and abundant phospholipids (principally C18:2). This preparation opens a new avenue for investigating essential aspects of phototransduction.

Circadian and pharmacological regulation of casein kinase I in the hamster suprachiasmatic nucleus.

In mammals, the mechanism for the generation of circadian rhythms and entrainment by light-dark (LD) cycles resides in the hypothalamic suprachiasmatic nuclei (SCN), and the principal signal that adjusts this biological clock with environmental timing is the light:dark cycle. Within the SCN, rhythms are generated by a complex of molecular feedback loops that regulate the transcription of clock genes, including per and cry. Posttranslational modification plays an essential role in the regulation of biological rhythms; in particular, clock gene phosphorylation by casein kinase I , both epsilon (CKIepsilon) and delta (CKIdelta), regulates key molecular mechanisms in the circadian clock. In this paper, we report for the first time that CKI activity undergoes a significant circadian rhythm in the SCN (peaking at circadian time 12, the start of the subjective night), and its pharmacological inhibition alters photic entrainment of the clock, indicating that CKI may be a key element in this pathway.

Gene expression profiling of light-induced retinal degeneration in phototransduction gene knockout mice

Exposure to light can induce photoreceptor cell death and exacerbate retinal degeneration. In this study, mice with genetic knockout of several genes, including rhodopsin kinase (Rhok-/-), arrestin (Sag-/-), transducin (Gnat1-/-), c-Fos (c-Fos-/-) and arrestin/transducin (Sag-/-/Gnat1-/-), were examined. We measured the expression levels of thousands of genes in order to investigate their roles in phototransduction signaling in light-induced retinal degeneration using DNA microarray technology and then further explored the gene network using pathway analysis tools. Several cascades of gene components were induced or inhibited as a result of corresponding gene knockout under specific light conditions. Transducin deletion blocked the apoptotic signaling induced by exposure to low light conditions, and it did not require c-Fos/AP-1. Deletion of c-Fos blocked the apoptotic signaling induced by exposure to high intensity light. In the present study, we identified many gene transcripts that are essential for the initiation of light-induced rod degeneration and proposed several important networks that are involved in pro- and anti-apoptotic signaling. We also demonstrated the different cascades of gene components that participate in apoptotic signaling under specific light conditions.

Early Reversible Changes on ERG in Pharmaceutically Induced Retinal Degeneration in Rats

PURPOSE: To evaluate the early ERG (electroretinogram) changes in N-methyl-N-nitrosourea (MNU)-induced retinal degeneration in rats. METHODS: Thirty-six 6-week-old male rats were injected intraperitoneally with 60mg/kg MNU and divided into 6 groups. Histology and ERG were recorded for the rats of each group before treatment and at 3, 6, 12, 18, and 24 hours after MNU injection. Promptly after the ERG recording, rats were sacrificed and the eyeballs prepared for histologic sectioning. The Tdt-mediated dUTP-digoxigenin nick end labeling (TUNEL) method was used to detect photoreceptor cell death. RESULTS: The first decreases of ERG responses were noticed maximally at 3 hours after the treatment. Thereafter, the amplitude of the responses was partially recovered at 12 hours post-treatment. The second decrease of ERG amplitudes was observed in the 18-hour recordings, and those changes progressed to 24 hours after the treatment. In the histologic findings, TUNEL (+) cells in the Outer Nuclear Layer (ONL) were not detected at 3 hours after MNU injection, but were initially noticed at 6 hours post-injection. CONCLUSIONS: The first decreases of ERG amplitudes proceeded the appearance of TUNEL (+) cells in ONL, and these electrophysiological changes seemed to not be related to photoreceptor cell death. We propose that electrophysiological changes observed might be related to the MNU-induced activity enhancement of guanylate cyclase in the phototransduction pathway. We also show that photoreceptor cell death in the MNU-induced retinal degeneration model occurs at 6 hours after the treatment, which is earlier than the results of previous reports.

Wave onset in central gray matter - its intrinsic optical signal and phase transitions in extracellular polymers

The brain is an excitable media in which excitation waves propagate at several scales of time and space. ''One-dimensional'' action potentials (millisecond scale) along the axon membrane, and spreading depression waves (seconds to minutes) at the three dimensions of the gray matter neuropil (complex of interacting membranes) are examples of excitation waves. In the retina, excitation waves have a prominent intrinsic optical signal (IOS). This optical signal is created by light scatter and has different components at the red and blue end of the spectrum. We could observe the wave onset in the retina, and measure the optical changes at the critical transition from quiescence to propagating wave. The results demonstrated the presence of fluctuations preceding propagation and suggested a phase transition. We have interpreted these results based on an extrapolation from Tasaki's experiments with action potentials and volume phase transitions of polymers. Thus, the scatter of red light appeared to be a volume phase transition in the extracellular matrix that was caused by the interactions between the cellular membrane cell coat and the extracellular sugar and protein complexes. If this hypothesis were correct, then forcing extracellular current flow should create a similar signal in another tissue, provided that this tissue was also transparent to light and with a similarly narrow extracellular space. This control tissue exists and it is the crystalline lens. We performed the experiments and confirmed the optical changes. Phase transitions in the extracellular polymers could be an important part of the long-range correlations found during wave propagation in central nervous tissue

Changes of Ionic Flow through the Internal Limiting Membrane during the Visual Adaptation of Vertebrate Eye

It already has been known that various ions were participated in phototransduction mechanism of the vertebrate photoreceptor during the visual adaptation. The vitreous humor(VH)contains certain amount of Na+, K+ and Ca++ as well. However, the roles of these ions are unknown except functioning of metabolic process. Our preliminary electroretinogram(ERG) experiments suggested that the permeability of these ions has light dependent activity during the light illumination. We have supported this suggestion more tangibly by trying out various experiments with bullfrog eyes as a reference of visual adaptation. The results are summarized as follows: 1)According to our atomic absorption spectroscopic measurements, the concentration of Na+, K+ and Ca++ in light adapted VH was higher than that of dark adapted VH. This result indicated that the light-dependention transport systems which affect the ionic movements might be in internal limiting membrane(ILM). 2)The amplitude of ERG b-wave was reduced by concentration decrement of Na+ and concentration increment of K+ respectively. On the other hand, the elimination of Ca++ within ringer solution resulted in b-wave amplitude increment. 3)Treatment of Na+ hannel blockers(TTX, STX)and K+ channel blockers(Ba++, Cd++, Cs+, 4-AP and TEA)in the vitreous humor side induced the increment and the decrement of b-wave response respectively. Taken together, these results suggest that the light dependent Na+ K+ channels exist in the ILM of vertebrate retina which participates visual adaptation.

The second messenger for visual excitation in invertebrate phototransduction

Invertebrate visual transduction involves a second messenger cascade process that leads to an increase in membrane conductance. The identity of the second messenger that gates the light-dependent channels is presently a major focus of attention. Cyclic GMP, inositol trisphosphate and Ca2+ are the most likely candidates for being such a messenger in the species studied so far. Here we review the available evidence for each of these molecules

Desenvolvimento de oxímetro para medidas em linhas de circulaçäo sangüínea extra-corpórea / Development of an oximeter for measures in line of extracorporeal blood circulation

Este trabalho descreve a construção de um protótipo de equipamento para medir a saturação de oxigênio (SaO2) nas linhas de perfusão arterial e venosa em procedimentos cirúrgicos com circulação extra-corpórea (CEC). O protótipo é constituído por dois sensores ópticos (um para linha arterial e outro para a venosa) e um módulo de processamento. Cada sensor contém dois LEDs e um fotodiodo que mede a luz transmitida na camada de sangue. O acoplamento entre o sensor e o sangue é obtido através de uma cubeta especial. A intensidade luminosa é digitalizada e processada para o cálculo da SaO2. O resultado é apresentado no painel frontal em um LCD. Testes In vitro mostraram boa correlação com valores de saturação determinados por aparelho comercial.

Abstract - This work desc1ibes a prototype for assessment of the oxygen saturation (OS) in flowing whole blood through the arterial and venous tubing used in extra-corporeal circulation (ECC) equipment dming cardiopulmonary bypass surgical procedures. The prototype utilizes an optical trar1sducer Vvith two LEDs and a photodiode operating in transmittance mode. A special cuvette was developed allowing easy attachment of the transducer to the tubings without causing hremolisis. The analog signal from light transmitted through blood is conve1ted to digital ar1d fed a microcontroller chip for further processing. The result is shown on the front panei on a LCD. ln vitro tests resulted in high coITelation between the readings provided by the prototype and a commercial blood gas analyzer