Low-Intensity picosecond fluorescence kinetics and excitation dynamics in barley chloroplasts

The fluorescence decays of barley chloroplasts have been measured by single-photon counting with tunable picosecond dye laser excitation. The fluorescence decays of dark-adapted chloroplasts are best fitted to a sum of three exponential lifetime components with lifetimes of 112, 380 and 2214 ps. The relative magnitude of each component is shown to be dependent on the excitation wavelength and collected emission wavelength. The excitation wavelength dependence is correlated with the Photosystem (PS) I and PS II action study of Ried [36] and with the measured pigment distributions in the photosynthetic unit [37,41]. Experiments varying the single excitation pulse intensity from 10⁸ to 10¹² photons/cm² pulse show that our results are not distorted by singlet-singlet annihilation. Unflowed samples where the cloroplasts are under constant illumination show 2-fold increases in quantum yield of fluorescence primarily in the two longer lifetime components. Theoretical calculations of Shipman [31] on an isolated reaction center with a homogeneous antenna are discussed and the principles extended to discussion of the measured barley chloroplast fluorescence decay components in terms of photosynthetic unit light-harvesting array models and earlier experimental work. Our data support a photosynthetic unit model in which 70–90% of the photons absorbed are quenched by either PS I or efficiently quenching PS II in a process where the fluorescence lifetime is 100 ps. The origin of the intermediate 380 ps. component is probably due to excitation transfer to a PS II reaction center in a redox state which quenches less efficiently.     

Test Study on the Excitation Spectrum of the CO ⃛Ar van der Waals Molecule

In the present contribution, we performed ab initio Møller-Plesset perturbation theory second-order (MP2) calculations in the framework of the supermolecule approach on the vertical excitation spectra of the weakly bound van der Waals CO-Ar molecule in its "near T-shaped" most stable ground state structure, as a guideline for future theoretical and experimental work. These test calculations indicate a ground CO ( X 1 D )- Ar ( 1 S ) interaction with R e =3.72 Å, D e =109 cm -1 and D o =92 cm -1 . They also indicate an excited CO ( A 1 @ )- Ar ( 1 S ) interaction with R e =3.55 Å, D e =141 cm -1 and D o =121 cm -1 . A red shift of 29 cm -1 for the CO ( X 1 D )- Ar ( 1 S ) M CO ( A 1 @ )- Ar ( 1 S ) vertical excitation energy, with respect to the corresponding CO ( X 1 D ) M CO ( A 1 @ ) excitation in the absence of Ar, can be obtained by comparing the corresponding D o values.     

Photosynthesis research in Italy: a review

This historical review was compiled and edited by Giorgio Forti, whereas the other authors of the different sections are listed alphabetically after his name, below the title of the paper; they are also listed in the individual sections. This review deals with the research on photosynthesis performed in several Italian laboratories during the last 50 years; it includes research done, in collaboration, at several international laboratories, particularly USA, UK, Switzerland, Hungary, Germany, France, Finland, Denmark, and Austria. Wherever pertinent, references are provided, especially to other historical papers in Govindjee et al. [Govindjee, Beatty JT, Gest H, Allen JF (eds) (2005) Discoveries in Photosynthesis. Springer, Dordrecht]. This paper covers the physical and chemical events starting with the absorption of a quantum of light by a pigment molecule to the conversion of the radiation energy into the stable chemical forms of the reducing power and of ATP. It describes the work done on the structure, function and regulation of the photosynthetic apparatus in higher plants, unicellular algae and␣in photosynthetic bacteria. Phenomena such as photoinhibition and the protection from it are also included. Research in biophysics of photosynthesis in Padova (Italy) is discussed by G.M. Giacometti and G.␣Giacometti (2006).     

可描述横向电场中外周神经兴奋的电缆方程

传统的电缆方程只能用于描述纵向电场中外周神经的兴奋,无法描述外周神经在横向电场作用下的兴奋,其于两阶段过程模型,提出一种改进的电缆方程,可以描述外周神经在横向电场中的兴奋,其结果和Struijk的离体实验数据相吻合。此改进的电缆方程可用于描述任意电场中外周神经的兴奋。     

Direct evidence for excitonically coupled chlorophylls a and b in LHC II of higher plants by nonlinear polarization spectroscopy in the frequency domain

Occurrence of excitonic interactions in light-harvesting complex II (LHC II) was investigated by nonlinear polarization spectroscopy in the frequency domain (NLPF) at room temperature. NLPF spectra were obtained upon probing in the chlorophyll (Chl) a/b Soret region and pumping in the Q_y region. The lowest energy Chl a absorbing at 678 nm is strongly excitonically coupled to Chl b.     

Dipole source localization by the mottled sculpin II. The role of lateral line excitation patterns

Extracellular, single unit recording techniques were used to measure the responses of posterior lateral line nerve fibers to a 50-Hz dipole source that slowly changed its location along the length of the fish. The flow-field equations for a dipole source were used to model the pressure gradient pattern and thus, the expected excitation pattern along a linear array of lateral line receptor organs for different source locations. Finally, excitation patterns were similarly modeled along the left and right side of the fish's head for actual steps taken by sculpin in approach pathways to the 50-Hz dipole source. Spatial histograms of posterior lateral line nerve fiber responses to different locations of the dipole source could be predicted from pressure gradient patterns modeled from the flow-field equations, confirming that the modeling approach applied to behavioral results was a good predictor of excitation patterns likely to be encoded by the lateral line periphery. An examination of how modeled excitation patterns changed from one position to the next in typical approach pathways and how patterns differed between positions from which successful and unsuccessful strikes were launched suggests that approach and strike strategies can indeed be explained by the information available in excitation patterns. In particular, changes in the spatial distribution of pressure gradient directions (polarities), available only when the source is lateral (as opposed to directly in front of the fish), appear to enhance the ability of sculpin to determine source distance. Without such information, misses are more likely to occur and successful strikes are more likely to be launched from short distances only. Accepted: 23 October 1996     

Excitatory Amino Acids: Studies on the Biochemical and Chemical Stability of Ibotenic Acid and Related Compounds

The complex pharmacological profile (excitation/inhibition) of ibotenic acid on single neurons in the mammalian CNS prompted studies on the stability of ibotenic acid and a number of structurally related excitatory amino acids under different in vitro conditions in the presence or absence of enzymes. Ibotenic acid, (RS)-3-hydroxy-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-7-carboxylic acid (7-HPCA), (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), and (RS)-alpha-amino-3-hydroxy-4-bromo-5-isoxazolepropionic acid (4-Br-homoibotenic acid) were all inhibitors of (S)-glutamic acid decarboxylase (GAD) in mouse brain homogenates, but only ibotenic acid was shown to undergo decarboxylation during incubation with brain homogenates. The formation of the decarboxylated product, muscimol, which primarily occurred in a synaptosomal fraction, was dependent on the presence of pyridoxal-5-phosphate (PALP) and was inhibited by (S)-glutamic acid, 3-mercaptopropionic acid (3MPA), aminooxyacetic acid (AOAA), and allyglycine, suggesting that ibotenic acid is a substrate for GAD. The overall decomposition rate for ibotenic acid (8.7 nmol min-1 mg-1 of protein), which apparently embraces other reactions in addition to decarboxylation to muscimol, was higher than the rate of decarboxylation of (S)-glutamic acid (3.2 nmol min-1 mg-1 of protein). At pH 7.4 and 37 degrees C, but in the absence of enzymes, none of the excitatory amino acids under study underwent any detectable decomposition, whereas ibotenic acid and 7-HPCA, but not AMPA and 4-Br-homoibotenic acid, decomposed, partially by decarboxylation, at 100 degrees C in a pH-dependent manner. In the presence of liver homogenates, ibotenic acid was also shown to decompose.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mechanism of Change in the Cation-Induced Excitation Energy Distribution Between PSⅡ and PS Ⅰ in the Chloroplast Membrane from Zostera marina

The interrelations between thylakoid polypeptide components and Mg2+-induced Chl a fluorescence and thylakoid surface charge changes were investigated in Zostera marina chloroplasts treated with Ca2+ and trypsin. It was observed that: 1. The increase of Mg2+- induced PS Ⅱ fluorescence intensity was closely related to the decrease of Mg2+-induced surface charge density of the thylakoid membrane in the normal chloroplast; 2. Removal of the 32～34 kD polypeptides of the thylakoid surface by Ca2+ extraction of the chloroplast did not affect the Mg2+-induced phenomena; 3. If the Ca2+-treated chloroplast was further digested by trypsin to remove the 26 kD polypeptide of the membrane surface, the Mg2+-induced phenomena disappeared completely. These results clearly indicated that the 26 kD polypeptide of thylakoid surface is the specific acting site of the cation that induced these two correlated phenomena in the chloroplast from Zostera marina. The mechanism on the regulating effect of the cation on excitation energy distribution between PS Ⅱ and PS Ⅰ was discussed.     

Dissolved organic carbon and fluorescence in Lake Hovsgol: factors reducing humic content of the lake water

 Lake Hovsgol is a large tectonic lake located in northern Mongolia, which has extremely transparent lake water. In our survey, the dissolved organic carbon of the lake water was 80–100 μM-C, and the fluorescence intensity in an excitation and emission matrix was very low. The brown color and high content of humic substances in river water flowing from a watershed consisting of grassland and forests rapidly declined in the coastal area of the lake. The decrease in humic content may be due not only to dilution by the lake water but also to flocculation and photobleaching. Among tectonic lakes in Asia, Lake Hovsgol would appear to have unique biological and hydrological features that reduce humic content and help to maintain water transparency. Received: June 25, 2002 / Accepted: January 10, 2003 Acknowledgments The authors acknowledge helpful discussion with Dr. J. Urabe. We thank Dr. T. Galbaatar, Mongolian Academy of Science, Mongolia, for his arrangements on the expeditions in 1999. We are also indebted to Mr. D. Hadbaatar, B. Ganbat, and the cruise staff of the R/V Suchbaatar for their assistance in the course of the study. This study was supported by Grant-in-Aid No. 09041159 and 13575034 for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Correspondence to:K. Hayakawa