Properties of the reaction center of the thermophilic purple photosynthetic bacterium Chromatium tepidum

Reaction centers were purified from the thermophilic purple sulfur photosynthetic bacterium Chromatium tepidum. The reaction center consists of four polypeptides L, M, H and C, whose apparent molecular masses were determined to be 25, 30, 34 and 44 kDa, respectively, by polyacrylamide gel electrophoresis. The heaviest peptide corresponds to tightly bound cytochrome. The tightly bound cytochrome c contains two types of heme, high-potential c-556 and low-potential c-553. The low-potential heme is able to be photooxidized at 77 K. The reaction center exhibits laser-flash-induced absorption changes and circular dichroism spectra similar to those observed in other purple photosynthetic bacteria. Whole cells contain both ubiquinone and menaquinone. Reaction centers contain only a single active quinone; chemical analysis showed this to be menaquinone. Reaction center complexes without the tightly bound cytochrome were also prepared. The near-infrared pigment absorption bands are red-shifted in reaction centers with cytochrome compared to those without cytochrome.     

Evidence for slow turnover in a fraction of Photosystem II complexes in thylakoid membranes

We used two different techniques to measure the recovery time of Photosystem II following the transfer of a single electron from P-680 to Q_A in thylakoid membranes isolated from spinach. Electron transfer in Photosystem II reaction centers was probed first by spectroscopic measurements of the electrochromic shift at 518 nm due to charge separation within the reaction centers. Using two short actinic flashes separated by a variable time interval we determined the time required after the first flash for the electrochromic shift at 518 nm to recover to the full extent on the second flash. In the second technique the redox state of Q_A at variable times after a saturating flash was monitored by measurement of the fluorescence induction in the absence of an inhibitor and in the presence of ferricyanide. The objective was to determine the time required after the actinic flash for the fluorescence induction to recover to the value observed after a 60 s dark period. Measurements were done under conditions in which (1) the electron donor for Photosystem II was water and the acceptor was the endogenous plastoquinone pool, and (2) Q₄₀₀, the Fe²⁺ near Q_A, remained reduced and therefore was not a participant in the flash-induced electron-transfer reactions. The electrochromic shift at 518 nm and the fluorescence induction revealed a prominent biphasic recovery time for Photosystem II reaction centers. The majority of the Photosystem II reaction centers recovered in less than 50 ms. However, approx. one-third of the Photosystem II reaction centers required a half-time of 2–3 s to recover. Our interpretation of these data is that Photosystem II reaction centers consist of at least two distinct populations. One population, typically 68% of the total amount of Photosystem II as determined by the electrochromic shift, has a steady-state turnover rate for the electron-transfer reaction from water to the plastoquinone pool of approx. 250 e⁻ / s, sufficiently rapid to account for measured rates of steady-state electron transport. The other population, typically 32%, has a turnover rate of approx. 0.2 e⁻ / s. Since this turnover rate is over 1000-times slower than normally active Photosystem II complexes, we conclude that the slowly turning over Photosystem II complexes are inconsequential in contributing to energy transduction. The slowly turning over Photosystem II complexes are able to transfer an electron from P-680 to Q_A rapidly, but the reoxidation of Q⁻_A is slow (t1/2 = 2 s). The fluorescence induction measurements lead us to conclude that there is significant overlap between the slowly turning over fraction of Photosystem II complexes and PS II_β reaction centers. One corollary of this conclusion is that electron transfer from P-680 to Q_A in PS II_β reaction centers results in charge separation across the membrane and gives rise to an electrochromic shift.     

Mesotocin and vasotocin in the brain of the lizard Gekko gecko

Summary The distribution of mesotocin and vasotocin was studied in the brain of the lizard Gekko gecko with antisera specific for either peptide. Both mesotocinergic and vasotocinergic perikarya are found in the paraventricular and supraoptic nuclei of the hypothalamus, whereas vasotocinergic neurons are exclusively present in the bed nucleus of the stria terminalis and in a cell group of the rhombencephalon. The distributional pattern of the mesotocinergic fibers corresponds closely to that of the vasotocinergic fibers. However, throughout the entire brain the mesotocinergic innervation is less dense than the vasotocinergic innervation. No sex differences are present in the mesotocinergic fiber system.Abbreviations acc nucleus accumbens - bst bed nucleus of the stria terminalis - bv blood vessel - dB diagonal band of Broca - dc dorsal cortex - dth dorsolateral thalamic nucleus - lc lateral cortex - me median eminence - oc optic chiasma - ot optic tract - pag periaqueductal grey - pvn paraventricular nucleus - rc rhombencephalic cell group - sep septum - son supraoptic nucleus - tect mesencephalic tectum - vth ventrolateral thalamus     

广西种子植物小资料

几年来,我所在中草药资源调查工作中,发现一些我国及广西未曾记录过的植物,现整理成文,以供有关部门参考。本文引用的标本均收藏在广西中医药研究所植物标本室(GXMI)。 山椒子水番挑(博白)番落技科Annonaceae Uvar花a grandiflora Roxb.in FI.Ind.2:665.1524;李秉滔,植物分类学报14(1):98.2976,蒋英,李秉滔,中国植物志30(2):26,图版10. 1979。 广西东南部:博白县,浪平公社,水库边1971年5月9日,王鉴均2247外北流县,隆盛公社,天堂,坡地疏林中,1977年9月26日北流调查队8一44口7。 分布:广东南部,广西东南部;印度、缅甸、泰国、越南、马来…     

Complete maps of IS1, IS2, IS3, IS4, IS5, IS30 and IS150 locations in Escherichia coli K12

Summary In this paper complete distribution maps are presented of the seven IS elements 1, 2, 3, 4, 5, 30 and 150. These maps were obtained during the construction of an almost complete restriction map of the Escherichia coli genome of K12 strain BHB2600. The positions of IS elements were correlated to this map. The distribution of integration sites of all IS types is nonrandom. Besides a large gap from 79 min to 96 min, there is a pronounced IS cluster at 6 min and another at 97 min, map locations that have low gene incidences on the classical map. One cluster coincides with a region of IS induced rearrangements. The IS distribution pattern was compared to patterns of strains W3110 and HB101.     

Why are there so many species of bumble bees at Dungeness?

WILLIAMS, P. H., 1989. Why are there so many species of bumble bees at Dungeness? Dungeness is unique in the British Isles in that it has more species of bumble bees than any other locality. Three ideas about what governs the number of species at a locality are examined by locking at patterns of flower visits at Dungeness in comparison with those at Shoreham, a species-poor locality also in Kent. The species of bumble bees that are present at Dungeness but absent from Shoreham show no association in their distributions among 2 km grid-squares in Kent with the species of food-plants that they prefer at Dungeness, nor is there any correlation between the diversity of bees and diversity of food-plants at Dungeness and Shoreham. From the information available, Dungeness is most likely to have more species of bumble bees because it has a particularly high density of the more nectar-rich flowers that bumble bees can use. Bumble bees feed most profitably from deep flowers because these contain more nectar than shallow flowers, although direct access to deeper flowers is ultimately limited by the length of each bee's proboscis. The distribution of worker proboscis lengths among species in the species-pool in Kent is clumped about a median of 7.9 mm. The best foraging conditions for the maximum number of species should be provided when flowers of similar depths are present in sufficiently large numbers for all foragers to make near-optimal flower choices. Although there is no difference in median between the distributions of the bees' proboscis lengths and the depths of the flowers they use at Dungeness, at Shoreham the flower depths used are shorter than the proboscis lengths. Among the food-plants at Dungeness, high densities of Teucrium scorodonia and Echium vulgare are likely to be especially important.     

Accumulation of cadmium and copper by the terrestrial snail Arianta arbustorum L.: kinetics and budgets

Summary Specimens of the terrestrial gastropod Arianta arbustorum were fed on cadmium- or copper-enriched agar plates with the aim of performing an input/output analysis and of studying the distribution of these metals in several organs of the snails. After a feeding period of 20 days about 45% of cadmium were lost. 36% accumulated in the hepatopancreas, where a cadmium concentration of more than 500 g/g was measured. The efficiency of cadmium assimilation decreased from about 90% at the beginning to about 55% after 20 days. Copper was distributed more evenly than cadmium, but the main site of copper storage seemed to be the foot/mantle tissues, where 49% of the ingested copper were found. The efficiency of copper assimilation always exceeded 95%. The patterns of distribution and assimilation of copper and cadmium are discussed in relation to differences in the cytological and biochemical detoxification mechanisms which exist for these metals in molluscs.     

Recovery of15N-labelled fertilizer by Coastal bermudagrass in lignite minesoil

Minesoils developed from lignite surface mining in Texas are nutrient-poor and have a high N retention capacity. A major concern of landowners and soil conservationists is the response of Coastal bermudagrass to the application of low rates of ammonium-N fertilizer on these nutrient-poor minesoils. A glasshouse study, using¹⁵N-labelled ammonium sulfate fertilizer and lignite minesoil, was conducted to measure Coastal bermudagrass biomass production and fertilizer recovery during establishment in response to clipping at 2, 4, and 8 week intervals. At N rates of 0, 40, and 80 kg N ha^–1,increases in N fertilization increased Coastal bermudagrass aboveground biomass 5-fold, but showed only small increases in belowground biomass. Recovery of ammonium-N fertilizer ranged from 54 to 63%. Roots contained approximately the same N content across all fertilizer rates suggesting that young, estabilishing, Coatal bermudagrass roots reserve N until their N requirement is met. As more N is obtained above that which was needed to maintain roots, then additional N taken up by the plant was transported to aboveground plant parts for growth. Frequent clipping intensified N transport to aboveground tissues. Reduced amounts of N were contained in roots after clipping due to reductions in root growth, biomass, and resource demand. Fertilization of Coastal bermudagrass at low N rates with different N fertilizer forms influenced the distribution of N in the plant and affected N recovery by different parts of the plant.     

Cultivar-related differences in the distribution of cell-wall-bound thionins in compatible and incompatible interactions between barley and powdery mildew

Leaf-specific thionins of barley (Hordeum vulgare L.) have been identified as a novel class of cell-wall proteins toxic to plant-pathogenic fungi and possibly involved in the defence mechanism of plants. The distribution of these polypeptides has been studied in the host-pathogen system of barley and Erisyphe graminis DC.f.sp. hordei Marchal (powdery mildew). Immunogold-labelling of thionins in several barley cultivars indicates that resistance or susceptibility may be attributed to the presence or absence of thionins at the penetration site in walls and papillae of epidermal leaf cells.All of the leaf-specific thionin genes are confined to the distal end of the short arm of chromosome 6 of barley. None of the genes for cultivarspecific resistance to powdery mildew which have previously been mapped on barley chromosomes are found close to this locus.