• Molecules and Cells
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• v.40 no.10
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• pp.773-786
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• 2017

The loss of green coloration via chlorophyll (Chl) degradation typically occurs during leaf senescence. To date, many Chl catabolic enzymes have been identified and shown to interact with light harvesting complex II to form a Chl degradation complex in senescing chloroplasts; this complex might metabolically channel phototoxic Chl catabolic intermediates to prevent oxidative damage to cells. The Chl catabolic enzyme 7-hydroxymethyl Chl a reductase (HCAR) converts 7-hydroxymethyl Chl a (7-HMC a) to Chl a. The rice (Oryza sativa) genome contains a single HCAR homolog (OsHCAR), but its exact role remains unknown. Here, we show that an oshcar knockout mutant exhibits persistent green leaves during both dark-induced and natural senescence, and accumulates 7-HMC a and pheophorbide a (Pheo a) in green leaf blades. Interestingly, both rice and Arabidopsis hcar mutants exhibit severe cell death at the vegetative stage; this cell death largely occurs in a light intensity-dependent manner. In addition, 7-HMC a treatment led to the generation of singlet oxygen ($^1O_2$) in Arabidopsis and rice protoplasts in the light. Under herbicide-induced oxidative stress conditions, leaf necrosis was more severe in hcar plants than in wild type, and HCAR-overexpressing plants were more tolerant to reactive oxygen species than wild type. Therefore, in addition to functioning in the conversion of 7-HMC a to Chl a in senescent leaves, HCAR may play a critical role in protecting plants from high light-induced damage by preventing the accumulation of 7-HMC a and Pheo a in developing and mature leaves at the vegetative stage.

• Korean Journal of Veterinary Research
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• v.36 no.1
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• pp.1-9
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• 1996

Functional and morphological characteristics of the exocrine pancreas in genetic model BB rat of insulin dependent diabetes medllitus(IDDM) were carried out. Wistar rat was used as control animal. Flow rate of pancreatic juice, output of amylase and protein, and plasma glucose and insulin levess were examined. Also light and ultrastructural characteristics of the exocrine pancreas were observed. Pancreatic flow rate, output of amylase and protein, and insulin level were lower;glucose level was higher comparing with those of the control Wistar rat. In Wistar rat, exocrine pancreas was typical light microscopically. Zymogen granules and cell organelles were well developed in fine structure. Cell size of the periinsular acini was larger, and number of zymogen granules were more than those of the teleinsular acini. Most acinar cells were dark cells which containe well-developed RER in their cytoplasm. On the other hand, some light cells which have the dilated RER cisterns were found. In BB rat exocrine pancreas, cell size of per-and tele-insular acini similar to that of Wistar rat. The number of light cells occupied 40-50% compairing with that of Wistar rat. Zymogen granules were lower in number than that of Wistar rat and divied into three types in morphological characteristics ; type I showing normal structure, type II showing the wide hallo and small electron dense core in center of the zymogen granule and type III not having the electron dense core in the zymogen granule. The present ratio of type I, type II and type III are less than 5%, 30-40% and more than 50%, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.47-47
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• 2011

There have been numerous efforts to enhance the efficiency of light-emitting diodes (LEDs) by using low dimensional structures such as quantum dots (QDs), wire (QWRs), and wells (QWs). We demonstrate QD/QWR/QW hybrid structured LEDs by using nano-scaled pyramid structures of GaN with ~260 nm height. Photoluminescence (PL) showed three multi-peak spectra centered at around 535 nm, 600 nm, 665 nm for QWs, QWRs, and QDs, respectively. The QD emission survived at room temperature due to carrier localization, whereas the QW emission diminished from 10 K to 300 K. We confirmed that hybrid LEDs had zero-, one-, and two-dimensional behavior from a temperature-dependent time-resolved PL study. The radiative lifetime of the QDs was nearly constant over the temperature, while that of the QWs increased with increasing temperature, due to low dimensional behavior. Cathodoluminescence revealed spatial distributions of InGaN QDs, QWRs, and QWs on the vertices, edges, and sidewalls, respectively. We investigated the blue-shifted electroluminescence with increasing current due to the band-filling effect. The hybrid LEDs provided broad-band spectra with high internal quantum efficiency, and color-tunability for visible light-emitting sources.

• Restorative Dentistry and Endodontics
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• v.41 no.4
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• pp.271-277
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• 2016

Objectives: In this study, we evaluated the influence of different radiant exposures provided by single-peak and polywave light-curing units (LCUs) on the degree of conversion (DC) and the mechanical properties of resin cements. Materials and Methods: Six experimental groups were established for each cement (RelyX ARC, 3M ESPE; LuxaCore Dual, Ivoclar Vivadent; Variolink, DMG), according to the different radiant exposures (5, 10, and $20J/cm^2$) and two LCUs (single-peak and polywave). The specimens were made (7 mm in length ${\times}$ 2 mm in width ${\times}$ 1 mm in height) using silicone molds. After 24 hours of preparation, DC measurement was performed using Fourier transform infrared spectrometry. The same specimens were used for the evaluation of mechanical properties (flexural strength, FS; elastic modulus, E) by a three-point bending test. Data were assessed for normality, after which two-way analysis of variance (ANOVA) and post hoc Tukey's test were performed. Results: No properties of the Variolink cement were influenced by any of the considered experimental conditions. In the case of the RelyX ARC cement, DC was higher when polywave LCU was used; FS and E were not influenced by the conditions evaluated. The LuxaCore cement showed greater sensitivity to the different protocols. Conclusions: On the basis of these results, both the spectrum of light emitted and the radiant exposure used could affect the properties of resin cements. However, the influence was material-dependent.

• BMB Reports
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• v.28 no.6
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• pp.499-503
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• 1995

In our previous studies (Chae et al., 1990; Chae et a1., 1993), we found that a phytochrome signal was clearly connected with the change in cytosolic free $Ca^{2+}$ concentration ($[Ca^{2+}]_i$) in oat cells. It was determined that the $[Ca^{2+}]_i$ change occured both by mobilization out of the intracellular $Ca^{2+}$ store and by influx from the medium. The specific aim of this work is to elucidate the processes connecting $Ca^{2+}$ mobilization and influx. The cells treated with thapsigargin (increasing $[Ca^{2+}]_i$ by inhibition of the $Ca^{2+}$-ATPase in the calcium pool) in the presence of external $Ca^{2+}$ showed the same increasing pattern (sustained increasing shape) of $[Ca^{2+}]_i$ as that measured in animal cells. Red light irradiation after thapsigargin treatment did not increase $[Ca^{2+}]_i$ These results suggest that thapsigargin also acts specifically in the processes of mobilization and influx of $Ca^{2+}$ in oat cells. When the cells were treated with TEA ($K^+$ channel blocker), changes in $[Ca^{2+}]_i$ were drastically reduced in comparison with that measured in the absence of TEA. The results suggest that the change in $[Ca^{2+}]_i$ due to red light irradiation is somehow related with $K^+$ channel opening to change membrane potential. The membrane potential change due to $K^+$ influx might be the critical factor in opening a voltage-dependent calcium channel for $Ca^{2+}$ influx.

• Animal cells and systems
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• v.9 no.3
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• pp.139-144
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• 2005

The attractant (orange light) or repellent (white light) signal is transmitted from SRI (Sensory Rhodopsin I) via protein-protein interaction with its transducer Htrl (Halobacterial Transducer for Sensory Rhodopsin I) which in turn controls a cytoplasmic phospho-transfer pathway that modulates flagella motor switching in Halobacterium salinarum. Some mutations in both SRI and Htrl showed an unusual mutant phenotype called inverted signaling, in which the cell produces a repellent response to normally attractant light. Twelve mutations at the Glutamate 56 (E56) position in the second transmembrane helix of Htrl were introduced by site-specific random mutagenesis. Almost all E56 mutants showed orange-light inverted responses in pH and temperature-dependent manners except E56D and E56Y. Except for these two mutants, all mutants accelerated the $S_{373}$ decay compared to wild-type at $18^{\circ}C$. This supported that there is an interaction between SRI and the second transmembrane of Htrl. Also a structural model of Htrl based on the Tar crystal structure and the secondary structure prediction program proposed the E56 residue to be in the middle of the proton channel. The most important observation is that the E56 mutant provides the evidence that this residue is very sensitive for signal relay, which can be explained by the open and closed conformations of the channel (A and R conformations) in SRI, as was postulated by the unified conformational shuttling model for transport and signaling.

• The Korean Journal of Physiology and Pharmacology
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• v.28 no.1
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• pp.49-57
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• 2024

While arterial tone is generally determined by the phosphorylation of Ser¹⁹ in myosin light chain (p-MLC2), Thr¹⁸/Ser¹⁹ diphosphorylation of MLC2 (pp-MLC2) has been suggested to hinder the relaxation of smooth muscle. In a dual-wire myography of rodent pulmonary artery (PA) and mesenteric artery (MA), we noticed significantly slower relaxation in PA than in MA after 80 mM KCl-induced condition (80K-contraction). Thus, we investigated the MLC2 phosphorylation and the expression levels of its regulatory enzymes; soluble guanylate cyclase (sGC), Rho-A dependent kinase (ROCK) and myosin light chain phosphatase target regulatory subunit (MYPT1). Immunoblotting showed higher sGC-α and ROCK2 in PA than MA, while sGC-β and MYPT1 levels were higher in MA than in PA. Interestingly, the level of pp-MLC2 was higher in PA than in MA without stimulation. In the 80K-contraction state, the levels of p-MLC2 and pp-MLC2 were commonly increased. Treatment with the ROCK inhibitor (Y27632, 10 µM) reversed the higher pp-MLC2 in PA. In the myography study, pharmacological inhibition of sGC (ODQ, 10 µM) slowed relaxation during washout, which was more pronounced in PA than in MA. The simultaneous treatment of Y27632 and ODQ reversed the impaired relaxation in PA and MA. Although treatment of PA with Y27632 alone could increase the rate of relaxation, it was still slower than that of MA without Y27632 treatment. Taken together, we suggest that the higher ROCK and lower MYPT in PA would have induced the higher level of MLC2 phosphorylation, which is responsible for the characteristic slow relaxation in PA.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
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• 2001.06a
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• pp.1182-1182
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• 2001

In this study, the newly constructed optical measurement system, which was mainly composed of a parametric tunable laser and a near infrared photoelectric multiplier, was introduced to clarify the optical characteristics of wood as discontinuous body with anisotropic cellular structure from the viewpoint of the time-of-flight near infrared spectroscopy (TOF-NIRS). The combined effects of the cellular structure of wood sample, the wavelength of the laser beam λ, and the detection position of transmitted light on the time resolved profiles were investigated in detail. The variation of the attenuance of peak maxima At, the time delay of peak maxima Δt and the variation of full width at half maximum Δw were strongly dependent on the feature of cellular structure of a sample and the wavelength of the laser beam. The substantial optical path length became about 30 to 35 times as long as sample thickness except the absorption band of water. Δt ${\times}$ Δw representing the light scattering condition increased exponentially with the sample thickness or the distance between the irradiation point and the end of sample. Around the λ=900-950 nm, there may be considerable light scattering in the lumen of tracheid, which is multiple specular reflection and easy to propagate along the length of wood fiber. Such tendency was remarkable for soft wood with the aggregate of thin layers of cell walls. When we apply TOF-NIRS to the cellular structural materials like wood, it is very important to give attention to the difference in the light scattering within cell wall and the multiple specular-like reflections between cell walls. We tried to express the characteristics of the time resolved profile on the basis of the optical parameters for light propagation determined by the previous studies, which were absorption coefficient K and scattering coefficient S from Kubelka-Munk theory and n from nth power cosine model of radiant intensity. The wavelength dependency of the product of K/S and n, which expressed the light-absorbing and -scattering condition and the degree of anisotropy, respectively, was similar to that of the time delay of peak maxima Δt. The variation of the time resolved profile is governed by the combination of these parameters. So, we can easily find the set of parameters for light propagation synthetically from Δt.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1755-1758
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• 2004

Misfiring is often observed during the high temperature quality assurancetest of plasma display panel. This limits the productivity of PDP industry. In this paper, experimental observations on the misfiring at high panel temperature have been performed through time dependent discharge light output and static margin measurement. For the high temperature condition, firing voltage increment is found in both surface and facing discharges. This in turn increases lime lag in address discharge, and results m increment of misfiring probability. In order to reduce this kind of misfiring, a new method that applies automatically different slope of ramp erasing pulse on the common electrode according to temperature variation is proposed. The experimental results show that controlling the slope of ramp erasing pulse is quite effective for compensating temperature-dependent variation of reset and address discharge.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.164-170
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• 2004

Misfiring is often observed during the high temperature quality assurance test of plasma display panel. This limits the productivity of PDP industry. In this paper, experimental observations on the misfiring at high panel temperature have been performed through time dependent discharge light output and static margin measurement. For the high temperature condition, firing voltage increment is found in both surface and facing discharges. This in turn increases time lag in address discharge, and results in increment of misfiring probability. In order to reduce this kind of misfiring, a new method that applies automatically different slope of ramp erasing pulse on the common electrode according to temperature variation is proposed. The experimental results show that controlling the slope of ramp erasing pulse is quite effective for compensating temperature-dependent variation of reset and address discharge.