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Light Induction (light + induction)
Selected AbstractsRhythm-Dependent Light Induction of the c-fos Gene in the Turkey HypothalamusJOURNAL OF NEUROENDOCRINOLOGY, Issue 6 2007A. Thayananuphat Day length (photoperiod) is a powerful synchroniser of seasonal changes in the reproductive neuroendocrine activity in temperate-zone birds. When exposed to light during the photoinducible phase, reproductive neuroendocrine responses occur. However, the neuroendocrine systems involved in avian reproduction are poorly understood. We investigated the effect of light exposure at different circadian times upon the hypothalamus and components of the circadian system, using c-fos mRNA expression, measured by in situ hybridisation, as an indicator of light-induced neuronal activity. Levels of c-fos mRNA in these areas were compared after turkey hens (on a daily 6-h light period) had been exposed to a 30-min period of light occurring at 8, 14, or 20 h after the onset of first light of the day (subjective dawn). Non-photostimulated control birds were harvested at the same times. In birds, photostimulated within the photoinducibile phase (14 h), in contrast to before or after, c-fos mRNA was significantly increased in the nucleus commissurae pallii (nCPa), nucleus premamillaris (PMM), eminentia mediana (ME), and organum vasculosum lamina terminalis (OVLT). Photostimulation increased c-fos mRNA expression in the pineal gland, nucleus suprachiasmaticus, pars visualis (vSCN) and nucleus inferioris hypothalami compared to that of their corresponding nonphotostimulated controls. However, the magnitudes of the responses in these areas were similar irrespective of where in the dark period the pulses occurred. No c-fos mRNA was induced in the nucleus infundibulari, in response to the 30-min light period at any of the circadian times tested. The lack of c-fos up-regulation in the pineal gland and vSCN following photostimulation during the photoinducible phase lends credence to the hypothesis that these areas are not involved in the photic initiation of avian reproduction. On the other hand, c-fos mRNA increases in the nCPa, ME, and OVLT support other studies showing that these areas are involved in the onset of reproductive behaviour initiated by long day lengths. The present study provides novel data showing that the PMM in the caudal hypothalamus is involved in the neuronally mediated, light-induced initiation of reproductive activity in the turkey hen. [source] The Heterotrimeric G-protein Complex Modulates Light Sensitivity in Arabidopsis thaliana Seed GerminationPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2009Javier F. Botto Release of dormancy and induction of seed germination are complex traits finely regulated by hormonal signals and environmental cues such as temperature and light. The Red (R):Far-Red (FR) phytochrome photoreceptors mediate light regulation of seed germination. We investigated the possible involvement of heterotrimeric G-protein complex in the phytochrome signaling pathways of Arabidopsis thaliana seed germination. Germination rates of null mutants of the alpha (G,) and beta (G,) subunits of the G-protein (Atgpa1-4 and agb1-2, respectively) and the double mutant (agb1-2/gpa1-4) are lower than the wildtype (WT) under continuous or pulsed light. The G, and G, subunits play a role in seed germination under hourly pulses of R lower than 0.1 ,mol m,2 s,1 whereas the G, subunit plays a role in higher R fluences. The germination of double mutants of G-protein subunits with phyA-211 and phyB-9 suggests that AtGPA1 seems to act as a positive regulator of phyA and probably phyB signaling pathways, while the role of AGB1 is ambiguous. The imbibition of seeds at 4°C and 35°C alters the R and FR light responsiveness of WT and G-protein mutants to a similar magnitude. Thus, G, and G, subunits of the heterotrimeric G-protein complex modulate light induction of seed germination by phytochromes and are dispensable for the control of dormancy by low and high temperatures prior to irradiation. We discuss the possible indirect role of the G-protein complex on the phytochrome-regulated germination through hormonal signaling pathways. [source] ELF4 is a phytochrome-regulated component of a negative-feedback loop involving the central oscillator components CCA1 and LHYTHE PLANT JOURNAL, Issue 2 2005Elise A. Kikis Summary Evidence has been presented that a negative transcriptional feedback loop formed by the genes CIRCADIAN CLOCK ASSOCIATED (CCA1), LATE ELONGATED HYPOCOTYL (LHY) and TIMING OF CAB (TOC1) constitutes the core of the central oscillator of the circadian clock in Arabidopsis. Here we show that these genes are expressed at constant, basal levels in dark-grown seedlings. Transfer to constant red light (Rc) rapidly induces a biphasic pattern of CCA1 and LHY expression, and a reciprocal TOC1 expression pattern over the first 24 h, consistent with initial induction of this synchronous oscillation by the light signal. We have used this assay with wild-type and mutant seedlings to examine the role of these oscillator components, and to determine the function of ELF3 and ELF4 in their light-regulated expression. The data show that whereas TOC1 is necessary for light-induced CCA1/LHY expression, the combined absence of CCA1 and LHY has little effect on the pattern of light-induced TOC1 expression, indicating that the negative regulatory arm of the proposed oscillator is not fully functional during initial seedling de-etiolation. By contrast, ELF4 is necessary for light-induced expression of both CCA1 and LHY, and conversely, CCA1 and LHY act negatively on light-induced ELF4 expression. Together with the observation that the temporal light-induced expression profile of ELF4 is counter-phased to that of CCA1 and LHY and parallels that of TOC1, these data are consistent with a previously unrecognized negative-feedback loop formed by CCA1/LHY and ELF4 in a manner analogous to the proposed CCA1/LHY/TOC1 oscillator. ELF3 is also necessary for light-induced CCA1/LHY expression, but it is neither light-induced nor clock-regulated during de-etiolation. Taken together, the data suggest (a) that ELF3, ELF4, and TOC1 all function in the primary, phytochrome-mediated light-input pathway to the circadian oscillator in Arabidopsis; and (b) that this oscillator consists of two or more interlocking transcriptional feedback loops that may be differentially operative during initial light induction and under steady-state circadian conditions in entrained green plants. [source] Chloroplast signalling in the light induction of nuclear HSP70 genes requires the accumulation of chlorophyll precursors and their accessibility to cytoplasm/nucleusTHE PLANT JOURNAL, Issue 4 2000Janette Kropat Summary Chlorophyll precursors Mg-protoporphyrin IX and its monomethylester are candidates for plastid-derived molecules involved in light signalling from the chloroplast to the nucleus. The pool sizes of these two Mg2+ -containing porphyrins and of protoporphyrin IX transiently increased upon a shift of Chlamydomonas cultures from dark to light. This increase coincided with the accumulation of mRNAs encoded by the nuclear genes HSP70A and HSP70B. Analysis of a mutant (brs-1), previously shown to be defective in the light induction of these genes, revealed high levels of protoporphyrin IX but no light-induced increase in the levels of Mg2+ -containing porphyrins. Inhibitors of cytoplasmic protein synthesis prevented both the light-induced rise in pool levels and induction of the HSP70 genes. Similarly, pre-gametes, intermediates of sexual differentiation, lacked both responses to light. The block in light induction of the HSP70 genes in inhibitor-treated cells and in pre-gametes could be circumvented by the exogenous addition of Mg-protoporphyrin IX in the dark. This suggests an essential role for light-induced Mg-protoporphyrin IX accumulation in this chloroplast-to-nucleus signalling pathway. However, accumulation of this porphyrin in the dark , presumably in the chloroplast , did not result in induction. A second crucial role for light in this signalling pathway is postulated which makes this plastidic compound accessible to the cytoplasm/nucleus where the downstream signalling pathway may be activated. [source] | ||||||||||