甘蔗伤流液中保绿活性物质的分离与初步鉴定

通过化学与物理学方法,从甘蔗(Sugar-cane)伤流液中分离出五种活性因素,对离体叶片有不同程度的保绿效应。依其化学性质判断,应属嘌呤化合物,可能是细胞分裂素物质。     

On the O2 flash yields of two cyanophytes

We explored O₂ flash yield in two cyanophytes, Anacystis nidulans and Agmenellum quadruplicatum. On a rate-measuring electrode, a single flash gave a contour of O₂ evolution with a peak at about 10 ms which was maximum (100) for 680 nm background light. On 625 nm illumination the peak was smaller (62) but was followed by an increased tail of O₂ attributed to enhancement of the background. After a period of darkness, repetitive flashes (5 Hz) gave a highly damped initial oscillation in individual flash yields which finally reached steady state at 94% of the yield for 680 nm illumination. When O₂ of repetitive flashes was measured as an integrated flash yield the results was distinctive and similar to that for a continuous light 1 (680 nm). An apparent inhibition of respiration which persisted into the following dark period was taken as evidence for the Kok effect. With a concentration-measuring electrode, integrated flash yield vs. flash rate showed the same nonlinear behavior as O₂ rate vs. intensity of light 1. We draw three conclusions about the two cyanophytes. (a) The plastoquinone pool is substantially reduced in darkness. (b) Because of a high ratio of reaction centers, reaction center 1 / reaction center 2, for the two photoreactions, saturating flashes behave as light 1. (c) Because repetitive flashes are light 1, they also give a Kok effect which must be guarded against in measurements designed to count reaction centers.     

Cuticular lesions induced in grass shrimp exposed to hexavalent chromium

Adult grass shrimp were exposed to four concentrations (0.5, 1.0, 2.0 and 4.0 ppm) of hexavalent chromium for 28 days. At the end of the exposure period, over 50% of the surviving shrimp possessed cuticular lesions that had many of the gross characteristics of “shell disease.” These lesions were usually associated with articulations of the appendages and abdomen. Furthermore, it was found that at increasing levels of chromium exposure, there was a proportionate increase in the loss of limbs such that nearly 50% of the limbs were lost in grass shrimp exposed to the highest test concentration of chromium. Histological and ultrastructural examination of numerous lesions demonstrated a range of degenerative features within the subcuticular epithelium that included cytoplasmic vacuolization, mitochondrial swelling, chromatin emargination, and the presence of unusual nuclear inclusions that appear to indicate direct chromium toxicity. Additionally, a marked retardation in new epicuticle and exocuticle formation was observed in viable tissues associated with lesions in late premolt shrimp. It is proposed that chromium interferes with the normal functions of subcuticular epithelium, particularly cuticle formation, and subsequently causes structural weaknesses or perforations to develop in the cuticle of newly moted shrimp. Because of these chromium-induced exoskeletal deficiencies, a viaduct for pathogenic organisms (e.g., bacteria) and direct chromium influx is formed that perpetuates lesion development.     

小麦颖果果皮绿色层内同化物的合成与分配

小麦幼嫩颖果中,果皮内侧发育出由内表皮与亚表皮组成的一薄层绿色组织。显微与亚显微结构观察表明,虽绿色层只接受到自然光照的1/4～1/8,叶绿体仍能正常发育,叶绿素含量与叶绿体数量均高出旗叶。大量胞间连丝联接相邻的绿色细胞,并在一定时期形成开放的胞间通道,显然有利于同化物的快速胞间运输。离体颖果饲喂~14CO_2试验证明,新合成的同化物从绿色细胞输向胚珠。绿色层产生的同化物可能通过合点端的珠心进入胚乳或通过珠孔直接汇聚到胚珠和分化中的原胚。     

Different long-term effects of bilateral and unilateral nucleus basalis lesions on rat cerebral cortical neurotransmitter content

Young adult rats received either unilateral or bilateral ibotenic acid infusions in their nucleus basalis, destroying most of the cholinesterase-staining neurons in that region. Cerebral cortex levels of choline acetyltransferase, somatostatin, neuropeptide Y, and monoamines were then assayed 2.5 and 10 months after bilateral lesions, or, 2.5, 10, and 14 months after unilateral lesions. Entorhinal and cerebral cortex levels of several amino acid transmitters were also measured. As expected, choline acetyltransferase activity was decreased in the frontal cortex ipsilateral to the ibotenic acid infusion in unilaterally or bilaterally lesioned animals. Parietal cortex concentrations of somatostatin and neuropeptide Y were altered by lesioning in a complicated, time-dependent manner. Thus, while unilateral lesions transiently decreased or had no effect on these neuropeptide levels, bilateral lesions elevated the level of each neuropeptide by over 100% at 10 months. Other cortical transmitter systems investigated appeared to be less affected by nucleus basalis-lesions. Unilateral lesions had no effect on prefrontal cortex norepinephrine, serotonin, or dopamine content at 14 months post-lesioning. These different neurochemical effects of unilateral and bilateral nucleus basalis lesions may be important for developing a model for the trans-synaptic effects of cortical cholinergic deafferentation.     

Isolation and characterization of the membrane-bound cytochrome c-554 from the thermophilic green photosynthetic bacterium Chloroflexus aurantiacus

The membrane-bound photooxidizable cytochrome c-554 from Chloroflexus aurantiacus has been purified. The purified protein runs as a single heme staining band on SDS-PAGE with an apparent molecular mass of 43 000 daltons. An extinction coefficient of 28 ± 1 mM^–1 cm^–1 per heme at 554 nm was found for the dithionite-reduced protein. The potentiometric titration of the hemes takes place over an extended range, showing clearly that the protein does not contain a single heme in a well-defined site. The titration can be fit to a Nernst curve with midpoint potentials at 0, +120, +220 and +300 mV vs the standard hydrogen electrode. Pyridine hemochrome analysis combined with a Lowry protein assay and the SDS-PAGE molecular weight indicates that there are a minimum of three, and probably four hemes per peptide. Amino acid analysis shows 5 histidine residues and 29% hydrophobic residues in the protein. This cytochrome appears to be functionally similar to the bound cytochrome from Rhodopseudomonas viridis. Both cytochrome c-554 from C. aurantiacus and the four-heme cytochrome c-558-553 from R. viridis appear to act as direct electron donors to the special bacteriochlorophyll pair of the photosynthetic reaction center. They have a similar content of hydrophobic amino acids, but differ in isoelectric point, thermodynamic characteristics, spectral properties, and in their ability to be photooxidized at low temperature.Abbreviations LDAO lauryl dimethyl amine-N-oxide - SDS-PAGE sodium dodecyl sulfate polyacrylamide gel electrophoresis - mV millivolt - E_m.8 midpoint potential at pH 8.0 - ODV optical density x volume in ml     

Fluorescence lifetimes of dimers and higher oligomers of bacteriochlorophyll c from Chlorobium limicola

Fluorescence lifetimes have been measured for bacteriochlorophyll (BChl) c isolated from Chlorobium limicola in different states of aggregation in non-polar solvents. Two different homologs of BChl c were used, one with an isobutyl group at the 4 position, the other with n-propyl. Species previously identified as dimers (Olson and Pedersen 1990, Photosynth Res, this issue) decayed with lifetimes of 0.64 ns for the isobutyl homolog, 0.71 ns for n-propyl. Decay-associated spectra indicate that the absorption spectrum of the isobutyl dimer is slightly red-shifted from that of the n-propyl dimer. Aggregates absorbing maximally at 710 nm fluoresced with a principal lifetime of 3.1 ns, independent of the homolog used. In CCl₄, only the isobutyl homolog forms a 747-nm absorbing oligomer spectrally similar to BChl c in vivo. This oligomer shows non-exponential fluorescence decay with lifetimes of 67 and 19 ps. Because the two components show different excitation spectra, the higher oligomer is probably a mixture of more than one species, both of which absorb at 747 nm.Abbreviations BChl bacteriochlorophyll - Chl chlorophyll - % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGGipm0dc9vqaqpepu0xbbG8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Xdm2aaW% baaSqabeaacaaIYaaaaaaa!3777!\[\chi ^2 \] chi-square - FWHM full-width at half-maximum     

Development of Photosystem II in dark grown Chlamydomonas reinhardtii. A light-dependent conversion of PS IIβ, QB-nonreducing centers to the PS IIα, QB-reducing form

The green alga Chlamydomonas reinhardtii is a facultative heterotroph and, when cultured in the presence of acetate, will synthesize chlorophyll (Chl) and photosystem (PS) components in the dark. Analysis of the thylakoid membrane composition and function in dark grown C. reinhardtii revealed that photochemically competent PS II complexes were synthesized and assembled in the thylakoid membrane. These PS II centers were impaired in the electron-transport reaction from the primary-quinone electron acceptor, Q_A, to the secondary-quinone electron acceptor, Q_B (Q_B-nonreducing centers). Both complements of the PS II Chl a–b light harvesting antenna (LHC II-inner and LHC II-peripheral) were synthesized and assembled in the thylakoid membrane of dark grown C. reinhardtii cells. However, the LHC II-peripheral was energetically uncoupled from the PS II reaction center. Thus, PS II units in dark grown cells had a -type Chl antenna size with only 130 Chl (a and b) molecules (by definition, PS II units lack LHC II-peripheral). Illumination of dark grown C. reinhardtii caused pronounced changes in the organization and function of PS II. With a half-time of about 30 min, PS II centers were converted froma Q_B-nonreducing form in the dark, to a Q_B-reducing form in the light. Concomitant with this change, PS II units were energetically coupled with the LHC II-peripheral complement in the thylakoid membrane and were converted to a PS II form. The functional antenna of the latter contained more than 250 Chl(a+b) molecules. The results are discussed in terms of a light-dependent activation of the Q_A-Q_B electron-transfer reaction which is followed by association of the PS II unit with a LHC II-peripheral antenna and by inclusion of the mature form of PS II (PS II) in the membrane of the grana partition region.Abbreviations Chl chlorophyll - PS photosystem - Q_A primary quinone electron acceptor of PS II - Q_B secondary quinone electron acceptor of PS II - LHC light harvesting complex - F₀ non-variable fluorescence yield - F_plf intermediate fluorescence yield plateau leyel - F_max maximum fluorescence yield - F_i initial fluorescence yield increase from F₀ to F_pl (F_pl–F₀) - F_v total variable fluorescence yield (F_m–F0) - DCMU dichlorophenyl-dimethylurea     

Influx and efflux of inorganic carbon in Synechococcus UTEX625

The CO₂ and HCO₃^? fluxes in air-grown cells of Synechococcus UTEX 625 al pH 8-0 were measured during dark to light and light to dark transitions using a mass spectrometer and sampling of the reaction medium. The kinetic parameters for initial uptake of CO₂ and HCO₃^? were determined during the initial period of illumination. The development of the internal C_i pool was followed up to steady-state photosynthesis, which occurred when the size of the internal inorganic carbon pool remained apparently constant for a limited period. The experimental procedure confirmed that only CO₂ transport occurred with 100mmolm^?3 Na⁺ and that both CO₂ and HCO^?3 transport occurred with 25molm^?3 Na⁺. The K_1/2 values of initial CO₂ and HCO₃ uptake were 0.7 and 17.2 mmolm^?3respectively and agreed closely with the K_1/2 values of net CO₂ and HCO₃^? transport during steady-state photosynthesis, which were 0.66 and 17.1 mmolm^?3 respectively. Maximum rates of CO₂and HCO₃^? transport were 423 and 219mmolh^?1 g^?1 Chl. Maximum CO₂ efflux observed upon darkening was 118mmolh^?1 g^?1 Chl. A permeability coefficient of the cell for CO₂ of 3 × 10^?8 m s^?1 was determined from the dark CO₂ efflux assuming an internal pH of 7.2 in the dark. Following the initial CO₂ uptake in the light, the extracellular [CO₂] steadily declined when only CO₂ transport was allowed, but an increase in the extracellular [CO₂] when HCO₃^? transport was allowed to proceed suggested that an enhanced CO₂ efflux occurred as a result of the larger size of the intracellular C_i pool.     

HCO3− and CO2 leakage from Synechococcus UTEX 625

The leakage of various inorganic carbon species from air-grown cells of Synechococcus UTEX 625 was investigated after a light to dark transition or during a light period using a mass spectrometer under a wide variety of experimental conditions. Total inorganic carbon efflux and CO₂ efflux during the initial period of darkness were measured with or without carbonic anhydrase in the reaction medium respectively. The HCO₃^? efflux after a light to dark transition was estimated by difference. Carbon dioxide efflux in the light was measured by inhibiting CO₂ transport with either Na₂S or COS₃ or quenching the ¹³C inorganic carbon transport by the addition of ¹²C inorganic carbon in excess. In cells in which CO₂ fixation was inhibited, when only the HCO₃^? transport system was fully operative, CO₂ effluxed continuously during the light period at a rate equal to about 25% of that in darkness. When only the CO₂ transport system was operative, HCO₃^? effluxed during the light period. The difference between the light and dark efflux rates was consistent with a 0.6 unit decrease in the intracellular pH upon darkening the cells. The permeabilities of the cell for CO₂ (2.94 ± 0.14 ± 10^?8ms^?1; mean ± SE, n=137) and HCO₃^? (1.4–1.7 ± 10^?9 ms^?1) were calculated.