共查询到20条相似文献，搜索用时 515 毫秒
1.
We prepared a molecular photodiode system in which the photocurrent direction can be switched by choosing the wavelength of an irradiating light. The molecular system is composed of two types of helical peptides that carry different chromophores and have different directions of dipole moments when they are immobilized on gold. The mixed, self-assembled monolayer generated an anodic photocurrent when one of the two chromophores was photoexcited, whereas the photocurrent switched to being cathodic when the other chromophore was photoexcited. The opposite current response arises from the dipole moment of each helical peptide, which accelerates electron transfer in the same direction. 相似文献
2.
Nagel G Ollig D Fuhrmann M Kateriya S Musti AM Bamberg E Hegemann P 《Science (New York, N.Y.)》2002,296(5577):2395-2398
Phototaxis and photophobic responses of green algae are mediated by rhodopsins with microbial-type chromophores. We report a complementary DNA sequence in the green alga Chlamydomonas reinhardtii that encodes a microbial opsin-related protein, which we term Channelopsin-1. The hydrophobic core region of the protein shows homology to the light-activated proton pump bacteriorhodopsin. Expression of Channelopsin-1, or only the hydrophobic core, in Xenopus laevis oocytes in the presence of all-trans retinal produces a light-gated conductance that shows characteristics of a channel selectively permeable for protons. We suggest that Channelrhodopsins are involved in phototaxis of green algae. 相似文献
3.
Mühlschlegel P Eisler HJ Martin OJ Hecht B Pohl DW 《Science (New York, N.Y.)》2005,308(5728):1607-1609
We have fabricated nanometer-scale gold dipole antennas designed to be resonant at optical frequencies. On resonance, strong field enhancement in the antenna feed gap leads to white-light supercontinuum generation. The antenna length at resonance is considerably shorter than one-half the wavelength of the incident light. This is in contradiction to classical antenna theory but in qualitative accordance with computer simulations that take into account the finite metallic conductivity at optical frequencies. Because optical antennas link propagating radiation and confined/enhanced optical fields, they should find applications in optical characterization, manipulation of nanostructures, and optical information processing. 相似文献
4.
Predacious mites fed for two generations solely on the eggs of wild-type spider mites responded normally to short day lengths by entering diapause. However, predacious mites fedfor two generations on eggs of albino spider mites, which are completely devoid of carotenoids, did not respond to short-day photoperiods. Apparently carotenoids are essential for photoperiodic induction; possibly a carotenoid or carotenoid derivative functions as the photopigment concerned in photoperiodic light reception in these mites. 相似文献
5.
Enzymes that produce retinal and related apocarotenoids constitute a sequence- and thus structure-related family, a member of which was analyzed by x-ray diffraction. This member is an oxygenase and contains an Fe2+-4-His arrangement at the axis of a seven-bladed beta-propeller chain fold covered by a dome formed by six large loops. The Fe2+ is accessible through a long nonpolar tunnel that holds a carotenoid derivative in one of the crystals. On binding, three consecutive double bonds of this carotenoid changed from a straight all-trans to a cranked cis-trans-cis conformation. The remaining trans bond is located at the dioxygen-ligated Fe2+ and cleaved by oxygen. 相似文献
6.
7.
弱光或低温弱光下辣椒叶片类胡萝卜素含量与品种耐性的关系 总被引：3，自引：0，他引：3
【目的】揭示弱光和低温弱光下辣椒叶片类胡萝卜素含量的变化规律,及其与品种耐弱光性或耐低温弱光性的关系,为辣椒种质耐性鉴定筛选适宜的指标和方法。【方法】以已知耐弱光性和耐低温弱光性的12个辣椒品种为试材,动态测定弱光和低温弱光下叶片类胡萝卜素含量,研究类胡萝卜素含量的变化规律及其与品种耐性的相关性。【结果】28℃/18℃、100μmol·m-2·s-1弱光处理或15℃/5℃、100μmol·m-2·s-1低温弱光处理均使辣椒叶片的类胡萝卜素含量逐渐降低,且低温弱光处理的降低幅度大于弱光处理的。28℃/18℃、100μmol·m-2·s-1弱光处理5、10、15和20d叶片的类胡萝卜素含量与辣椒耐弱光性综合隶属函数值均呈极显著正相关;15℃/5℃、100μmol·m-2·s-1低温弱光处理10、15和20d叶片的类胡萝卜素含量与辣椒耐低温弱光性综合隶属函数值呈显著负相关。【结论】弱光或低温弱光下辣椒叶片类胡萝卜素含量可以作为品种耐弱光性及耐低温弱光性的鉴定指标。弱光下辣椒叶片的类胡萝卜素含量越高,品种的耐弱光性越强;低温弱光下辣椒叶片的类胡萝卜素含量越低,品种的耐低温弱光性越强。 相似文献
8.
光质对油葵芽苗菜生长和品质的影响 总被引：4，自引：0，他引：4
采用发光二极管(light emitting diode,LED)调制光谱能量分布,以荧光灯作为对照,研究光质对油葵芽苗菜生长和品质的影响。研究表明:在光照强度23μmol.m-2.s-1、光周期14 h.d-1和温度(25±2)℃的条件下,红光处理显著提高子叶面积、下胚轴直径、淀粉含量、叶绿素总量/类胡萝卜素含量,与其他光质处理相比,红光下油葵芽苗菜叶绿素a、叶绿素总量和类胡萝卜素含量显著提高;蓝光显著提高芽苗菜干物质、可溶性蛋白含量及POD、CAT活性;黄光对根长有抑制效果,而对游离氨基酸的积累有促进作用;UV-B显著提高下胚轴长度和SOD、CAT的活性。综上所述,红光照射有利于油葵芽苗菜生长及品质提升。 相似文献
9.
Nagata T Koyanagi M Tsukamoto H Saeki S Isono K Shichida Y Tokunaga F Kinoshita M Arikawa K Terakita A 《Science (New York, N.Y.)》2012,335(6067):469-471
The principal eyes of jumping spiders have a unique retina with four tiered photoreceptor layers, on each of which light of different wavelengths is focused by a lens with appreciable chromatic aberration. We found that all photoreceptors in both the deepest and second-deepest layers contain a green-sensitive visual pigment, although green light is only focused on the deepest layer. This mismatch indicates that the second-deepest layer always receives defocused images, which contain depth information of the scene in optical theory. Behavioral experiments revealed that depth perception in the spider was affected by the wavelength of the illuminating light, which affects the amount of defocus in the images resulting from chromatic aberration. Therefore, we propose a depth perception mechanism based on how much the retinal image is defocused. 相似文献
10.
Role of chloroplast protein kinase Stt7 in LHCII phosphorylation and state transition in Chlamydomonas 总被引：1，自引：0，他引：1
Photosynthetic organisms adapt to changes in light quality by redistributing light excitation energy between two photosystems through state transition. This reorganization of antenna systems leads to an enhanced photosynthetic yield. Using a genetic approach in Chlamydomonas reinhardtii to dissect the signal transduction pathway of state transition, we identified a chloroplast thylakoid-associated serine-threonine protein kinase, Stt7, that has homologs in land plants. Stt7 is required for the phosphorylation of the major light-harvesting protein (LHCII) and for state transition. 相似文献
11.
A specific inactivator of chymotrypsin, p-azophenyldiphenylcarbamyl chloride, exists as two geometric isomers, cis and trans, which are interconvertible by means of light. The cis-isomer is five times more reactive than the more stable trans-isomer, and is obtained by exposure of the latter to light of 320 nanometer wavelength. The trans-isomer can be regained by exposure of the cis-isomer to light of 420 nanometer wavelength. This interconversion can be made to occur in aqueous solution in the presence of the enzyme under conditions in which the trans-isomer reacts relatively slowly with chymotrypsin. Thus, it is possible to regulate the rate of inactivation of chymotrypsin by using light of the appropriate wavelength. This system is presented as a model for some of the light-sensitive metabolic systems present in living organisms. 相似文献
12.
A broadly tunable picosecond laser source and an ultrafast streak camera were used to measure temporally and spectrally resolved emission from intact phycobilisomes and from individual phycobiliproteins as a function of excitation wavelength. Both wild-type and mutant phycobilisomes of the unicellular cyanobacterium Synechocystis 6701 were examined, as well as two biliproteins, R-phycoerythrin (240 kilodaltons, 34 bilins) and allophycocyanin (100 kilodaltons, 6 bilins). Measurements of intact phycobilisomes with known structural differences showed that the addition of an average of 1.6 phycoerythrin disks in the phycobilisome rod increased the overall energy transfer time by 30 +/- 5 picoseconds. In the isolated phycobiliproteins the onset of emission was as prompt as that of a solution of rhodamine B laser dye and was independent of excitation wavelength. This imposes an upper limit of 8 picoseconds (instrument-limited) on the transfer time from "sensitizing" to "fluorescing" chromophores in these biliproteins. These results indicate that disk-to-disk transfer is the slowest energy transfer process in phycobilisomes and, in combination with previous structural analyses, show that with respect to energy transfer the lattice of approximately 625 light-harvesting chromophores in the Synechocystis 6701 wild-type phycobilisome functions as a linear five-point array. 相似文献
13.
Assessment of retinal recognition technology as a biometric method for sheep identification 总被引：1，自引：0，他引：1
U. Gonzales Barron G. Corkery B. Barry F. Butler K. McDonnell S. Ward 《Computers and Electronics in Agriculture》2008,60(2):156-166
In order to assure effective traceability, food-producing animals must be identified by a tamper-proof and durable technique. With the advance in human biometric technologies, the deployment of retinal recognition technology for cattle identification and verification has been prompted. The objective of this study was to assess the accuracy of a commercially available retina biometric technology for sheep identification (i) by determining whether light conditions during retinal image capture (indoors and outdoors with shade) and different operators exerted any significant effect on the matching score of the built-in pattern matching algorithm; and (ii) by evaluating the recognition performance of the biometric system for enrolment of one retinal image per sheep and two retinal images per sheep (bimodal biometric system). Neither the light conditions nor the operators were found to have a statistically significant effect on the matching score values of the built-in algorithm; yet it was clear that the pupillary light reflex phenomenon played a major role in obtaining lower matching score values for retinal images taken outdoors. The recognition errors of the one-retina biometric system were estimated to be 0.25% for false matches and 0.82% for false non-matches. An improved bimodal biometric system, i.e., two retinas, that applies a decision criterion based on a simple OR logical operator and a sum of matching scores, has been proposed in this study in order to reduce both probabilities of false matches and false non-matches to near zero. 相似文献
14.
Holt NE Zigmantas D Valkunas L Li XP Niyogi KK Fleming GR 《Science (New York, N.Y.)》2005,307(5708):433-436
Photosynthetic light harvesting in excess light is regulated by a process known as feedback deexcitation. Femtosecond transient absorption measurements on thylakoid membranes show selective formation of a carotenoid radical cation upon excitation of chlorophyll under conditions of maximum, steady-state feedback deexcitation. Studies on transgenic Arabidopsis thaliana plants confirmed that this carotenoid radical cation formation is correlated with feedback deexcitation and requires the presence of zeaxanthin, the specific carotenoid synthesized during high light exposure. These results indicate that energy transfer from chlorophyll molecules to a chlorophyllzeaxanthin heterodimer, which then undergoes charge separation, is the mechanism for excess energy dissipation during feedback deexcitation. 相似文献
15.
Unusually large electric field effects have been measured for the absorption spectra of carotenoids (spheroidene) in the B800-850 light-harvesting complex from the photosynthetic bacterium Rhodobacter sphaeroides. Quantitative analysis shows that the difference in the permanent dipole moment between the ground state and excited states in this protein complex is substantially larger than for pure spheroidene extracted from the protein. The results demonstrate the presence of a large perturbation on the electronic structure of this nearly symmetric carotenoid due to the organized environment in the protein. This work also provides an explanation for the seemingly anomalous dependence of carotenoid band shifts on transmembrane potential and a generally useful approach for calibrating electric field-sensitive dyes that are widely used to probe potentials in biological systems. 相似文献
16.
Lucas RJ Freedman MS Muñoz M Garcia-Fernández JM Foster RG 《Science (New York, N.Y.)》1999,284(5413):505-507
In mammals, ocular photoreceptors mediate an acute inhibition of pineal melatonin by light. The effect of rod and cone loss on this response was assessed by combining the rd mutation with a transgenic ablation of cones (cl) to produce mice lacking both photoreceptor classes. Despite the loss of all known retinal photoreceptors, rd/rd cl mice showed normal suppression of pineal melatonin in response to monochromatic light of wavelength 509 nanometers. These data indicate that mammals have additional ocular photoreceptors that they use in the regulation of temporal physiology. 相似文献
17.
Stereodynamic complexes of copper were found to undergo inversion of a helical chiral element upon oxidation or reduction. The amino acid methionine was derivatized by the attachment of two chromophores to the nitrogen atom. The resultant ligands formed stable complexes with Cu(I) and Cu(II) salts. For a derivative of a given absolute chirality, the complexes afford nearly mirror image circular dichroism spectra. The spectral changes originate from reorientation of the nitrogen-attached chromophores due to a conformation interconversion driven by the exchange of a carboxylate for a sulfide ligand. The electrically induced chirality inversion coupled with strong interactions with polarized light is unique and may lead to novel chiral molecular devices. 相似文献
18.
以兰花‘霞光’组培苗为试验材料,采用LED光源发射的单色光谱红光(R)、蓝光(B)、绿光(G)和白光(W)等不同光质的配比组合光对组培苗进行处理,以荧光灯为对照(CK),研究不同光质对兰花‘霞光’组培苗生长和生理特性的影响。结果表明:(1)与CK相比,红蓝绿复合光(RBG)、单色红光(R)和红蓝复合光(1RB)对组培苗的株高、叶长、叶数、根长、根数等有影响,但与对照差异并不显著;1RB处理下植株的干重显著高于CK。(2)与CK相比,在白光光源(W)下,植株的可溶性蛋白含量最高,但与对照差异并不显著;在不同光质处理下,可溶性糖含量差异不显著。(3)红蓝白复合光(RBW)处理下,‘霞光’组培苗叶绿素a、叶绿素b和类胡萝卜素的含量最高,显著高于其他处理。相比之下,LED红蓝白复合光(RBW)处理下的‘霞光’组培苗长势最好,可替代普通荧光灯光源,作为‘霞光’组培苗生长的理想光源。 相似文献
19.
培养液铁离子浓度对单生卵囊藻和月牙藻细胞组成的影响 总被引：1，自引：0，他引：1
研究了培养液中添加不同量柠檬酸铁(0、0.0039、0.039和0.39 mg/L)对单生卵囊藻(Oocystis solitaria)和月牙藻(Selenastrum sp.)细胞组成的影响。结果表明,单生卵囊藻和月牙藻分别在柠檬酸铁添加量为0.039 mg/L和0.39 mg/L时具有最大的蛋白、总糖、叶绿素a和类胡萝卜素含量。单生卵囊藻和月牙藻均在柠檬酸铁添加量为0.39 mg/L时具有最大的总脂肪含量,分别为13.76%和22.78%,比相应未添加铁组分别提高了318%和160%。单生卵囊藻富含18:3n3,月牙藻富含18:2n6。培养液中高的铁离子浓度诱导两种藻细胞合成更多的饱和脂肪酸。相比单生卵囊藻,月牙藻对培养液中高铁离子浓度的耐受力更强,更适合作为生物柴油的原料。 相似文献
20.
Light pulses that shift rhythms induce gene expression in the suprachiasmatic nucleus 总被引：22，自引：0，他引：22
Lighting cycles synchronize (entrain) mammalian circadian rhythms by altering activity of cells in the suprachiasmatic nucleus (SCN) of the hypothalamus, a circadian pacemaker. Exposure of hamsters and rats to light pulses at those phases of the circadian rhythm during which light can shift the rhythm caused increased immunoreactivity for the product of the immediate-early gene c-fos in cells in the region of the SCN that receives retinal fibers. Light pulses also increased messenger RNA for the Fos protein and for the immediate-early protein NGFI-A in the rat SCN. Similar increases in mRNA for NGFI-A were seen in the SCN of hamsters. Thus cells in this portion of the SCN undergo alterations in gene expression in response to retinal illumination, but only at times in the circadian cycle when light is capable of influencing entrainment. 相似文献