A β-ketoacyl-acyl carrier protein synthase III gene (fabH) is encoded on the chloroplast genome of the red alga Porphyra umbilicalis

DNA sequencing of a region of the chloroplast genome of the red alga Porphyra umbilicalis revealed an open reading frame of 326 amino acids. Databank searches indicated that this ORF is 34% identical to an E. coli gene (fabH) encoding -ketoacyl-carrier protein synthase III. In addition, a leucine tRNA gene (trnL(GAG)) was detected just downstream. Neither of these genes are encoded on the chloroplast genomes of land plants.     

A comparison of the photosynthesis — light intensity relationship in phylogenetically different marine microalgae

Measured under equivalent physiological conditions, the photosynthesis-light intensity relationship based on oxygen production/mg chlorophyll a was found to be the same in five species representing the different chlorophyll c containing divisions of marine phytoplankton. Other non-photochemical metabolic processes related to photosynthesis such as diurnal variations, maximal photosynthesis rates, and dark oxygen uptake were quite different, and so these are the more significant factors in production and ecological distribution of diatoms, dinoflagellates, and coccolithophores. In contrast, the green algae tested showed a significantly different photosynthesis-light intensity curve from the chlorophyll c group.     

Essential role of the PSI–LHCII supercomplex in photosystem acclimation to light and/or heat conditions by state transitions

Light and temperature affect state transitions through changes in the plastoquinone (PQ) redox state in photosynthetic organisms. We demonstrated that light and/or heat treatment induced preferential photosystem (PS) I excitation by binding light-harvesting complex II (LHCII) proteins. The photosystem of wheat was in state 1 after dark overnight treatment, wherein PQ was oxidized and most of LHCII was not bound to PSI. At the onset of the light treatment [25 °C in the light (100 µmol photons m^?2 s^?1)], two major LHCIIs, Lhcb1 and Lhcb2 were phosphorylated, and the PSI–LHCII supercomplex formed within 5 min, which coincided with an increase in the PQ oxidation rate. Heat treatment at 40 °C of light-adapted wheat led to further LHCII protein phosphorylation of, resultant cyclic electron flow promotion, which was accompanied by ultrafast excitation of PSI and structural changes of thylakoid membranes, thereby protecting PSII from heat damage. These results suggest that LHCIIs are required for the functionality of wheat plant PSI, as it keeps PQ oxidized by regulating photochemical electron flow, thereby helping acclimation to environmental changes.     

Quantitative analysis of State 1–State 2 transitions in intact leaves using modulated fluorimetry — evidence for changes in the absorption cross-section of the two photosystems during state transitions

Using a combination of modulated and non-modulated light with synchronized detection it has been possible to monitor State 1–State 2 transitions in intact leaves as changes in the yield of modulated chlorophyll fluorescence. In the presence of excess far-red non-modulated light (713 nm) absorbed mainly by Photosystem I (PS I), the modulated fluorescence intensity was taken to represent F_o — the emission yield which occurs when the reaction centres of Photosystem II (PS II) are all open. On the other hand, superimposing saturating non-modulated wide-band, blue-green light resulted in a transitory maximum yield of modulated chlorophyll fluorescence, F_m, due to the total closure of the PS II reaction centres. In the absence of these additional lights the fluorescence level assumed a steady-state value, F_s, between F_o and F_m. All these parameters changed as the leaf slowly adapted to light of a given spectral composition. It was found that both F_o and F_m increased reversibly (by about 15–20%) during the transition from State 2 to State 1 such that the ratio of F_m to F_o remained constant, indicative of changes in absorption cross-section of PS II and PS I rather than alterations in ‘spillover’ which would cause preferential changes in F_m. It was also possible to estimate the fractions of light, β and α, channeled to PS II and PS I, respectively, from the values of F_o, F_m and F_s. In one approach, β was estimated in State 1, using the assumption that α + β = 1, and its variation during the subsequent state transition was assumed to follow proportional changes in F_o (or F_m). It was found that in State 2 there is a small loss (about 4%) of the total utilization of light in both photosystems. However, if such loss is neglected, assuming α + β is always unity, the calculated β was found to vary in the same direction and almost with the same magnitude as F_o (or F_m), indicating independently that a change in absorption cross-section in PS II (and PS I) had occurred. Consistent with these data were the light-saturation curves for the non-modulated far-red light-quenching effect in bringing the fluorescence from F_s to F_o in States 1 and 2. The ratio of the initial slopes of these curves indicates quantitatively both redistribution of light between PS I and PS II during the State 1–State 2 transitions and a partial loss of excitation energy in State 2.     

Ageing of chloroplasts in vitro — III. Comparison of the effects of ageing in vitro and senescence on the red absorption band and primary photochemical reactions of sunflower chloroplasts

A comparison of changes in absorption properties and electron transport activities of chloroplasts ageing in vivo and in vitro is made. Chloroplasts from sunflower leaves senescing in vivo during 7 days in dark do not show a blue shift of the red absorption band; in contrast, the shift becomes apparent within 24 h of in vitro ageing of isolated organelles. Photosynthetic activity by chloroplasts is lost much faster during in vitro than in vivo ageing. During in vitro ageing, the rate of degradation of thylakoid membranes as characterised by the shift in the red absorption band and loss in Hill reaction is further accelerated in chloroplasts isolated from dark-induced senescing leaves, suggesting the influence of the in vivo status of the chloroplasts on their in vitro stability.Abbreviations DCPIP 2,6-dichlorophenol indophenol - PSI Photosystem I - Chl Chlorophyll     

Crystallographic studies of the binding of ligands to the dicarboxylate site of Complex II,and the identity of the ligand in the “oxaloacetate-inhibited” state

Mitochondrial Complex II (succinate:ubiquinone oxidoreductase) is purified in a partially inactivated state, which can be activated by removal of tightly bound oxaloacetate (E.B. Kearney, et al., Biochem. Biophys. Res. Commun. 49 1115–1121). We crystallized Complex II in the presence of oxaloacetate or with the endogenous inhibitor bound. The structure showed a ligand essentially identical to the “malate-like intermediate” found in Shewanella Flavocytochrome c crystallized with fumarate (P. Taylor, et al., Nat. Struct. Biol. 6 1108–1112) Crystallization of Complex II in the presence of excess fumarate also gave the malate-like intermediate or a mixture of that and fumarate at the active site. In order to more conveniently monitor the occupation state of the dicarboxylate site, we are developing a library of UV/Vis spectral effects induced by binding different ligands to the site. Treatment with fumarate results in rapid development of the fumarate difference spectrum and then a very slow conversion into a species spectrally similar to the OAA-liganded complex. Complex II is known to be capable of oxidizing malate to the enol form of oxaloacetate (Y.O. Belikova, et al., Biochim. Biophys. Acta 936 1–9). The observations above suggest it may also be capable of interconverting fumarate and malate. It may be useful for understanding the mechanism and regulation of the enzyme to identify the malate-like intermediate and its pathway of formation from oxaloacetate or fumarate.     

Ageing of chloroplasts in vitro — III. Comparison of the effects of ageing in vitro and senescence on the red absorption band and primary photochemical reactions of sunflower chloroplasts

A comparison of changes in absorption properties and electron transport activities of chloroplasts ageing in vivo and in vitro is made. Chloroplasts from sunflower leaves senescing in vivo during 7 days in dark do not show a blue shift of the red absorption band; in contrast, the shift becomes apparent within 24 h of in vitro ageing of isolated organelles. Photosynthetic activity by chloroplasts is lost much faster during in vitro than in vivo ageing. During in vitro ageing, the rate of degradation of thylakoid membranes as characterised by the shift in the red absorption band and loss in Hill reaction is further accelerated in chloroplasts isolated from dark-induced senescing leaves, suggesting the influence of the in vivo status of the chloroplasts on their in vitro stability.Abbreviations DCPIP 2,6-dichlorophenol indophenol - PSI Photosystem I - Chl+ Chlorophyll     

Miocene—pliocene sea-level changes and volcanic phases on gran Canaria (Canary islands) in the light of new K—Ar ages

Thirteen new K—Ar dates of stratigraphically important Pliocene and Pleistocene lava flows and intrusives from Gran Canaria (Canary Islands) permit a more precise definition of alternating periods of volcanic activity and erosional intervals. The Miocene erosional interval (Erosional Interval I) lasted from 9.6 to 4.4 m.y. B.P.; Roque Nublo volcanic activity (phase II in the magmatic history of the island) began 4.4 m.y. and ended 3.7 m.y. ago; Erosional Interval II lasted from 3.7 to 2.8 m.y. B.P.; volcanic activity resumed at 2.8 m.y. B.P. with the eruption of olivine nephelinite lavas. The subsequent alternation of phases of volcanic activity and erosional intervals is not yet precisely dated. Four regressions and three transgressions are recognized on Gran Canaria in the time interval 9.6-2 m.y. B.P. The famous marine sediments of the “Las Palmas Terrace” represent at least three distinct marine levels of different ages and only the oldest one may correspond to the age assignment “Helvetian or Tortonian” of Rothpletz and Simonelli (1890).Several causes for the marine transgressions are discussed such as eustatic changes in sea level, isostatic vertical movements of the island and movements in regional stress fields. None of the transgressions and regressions can be convincingly explained so far by either a single mechanism or a combination of several processes. However, we tentatively suggest that eustatic and, perhaps to a lesser degree, isostatic movements are the main causes. These uncertainties in the interpretation of the transgressions and regressions underscore the need for more precise dating of similar elevated marine sedimentary rocks on other Atlantic islands.     

Structure-activity relationships for glucocorticoids—III. Structural and conformational study of the rings and side-chain of steroids which bind to the glucocorticoid receptor

The structure of fifteen steroids which bind to the glucocorticoid receptor has been determined by complete geometry optimisation. This method calculates the spatial atomic coordinates for each molecule in the conformation with the minimum internal constraint (lowest-energy state). In addition, the relative energy changes associated with a complete rotation of the side-chain have been calculated for nine of these steroids.The molecules in this series differ by their substituents at C11, C16, C17 and C21, and by a C1-C2 double bond. First we find that, except for the deformable A-ring and side-chain, the optimized structures are in good agreement with the available crystallographic ones.As to the structural influence of substituents, it is of course most evident in their immediate vicinity. More subtle effects which, however, become apparent when one considers the overall shape of the steroid, are discussed in the accompanying paper. In all optimized molecules except prednisolone (Δ1-cortisol). the A-ring is a 1α, 2β-half-chair. The different conformations seen by crystallography are consistent with the distortability of this ring. The rigid B- and C-rings all have similar chair conformations. The D-rings range from a 13β-envelope to a 13β, 14α-half-chair, depending on the substitution. Concerning the side-chain, all optimized molecules exhibit a C13-C17-C20-O20 torsion angle between 70° and 120°. The 17-H-substituted steroids have a mean angle of 79°. This value increases to 101° in the presence of a 17-hydroxyl group.Finally, the energetical curves corresponding to the complete rotation about the C17-C20 bond imposed to the side-chain are all different for the steroids studied. In each molecule, the range of energy changes is relatively small indicating the ability of the molecules to minimize the introduced perturbation. The hypothesis is formulated that receptor binding involves a specific conformation of the side-chain, different from the lowest energy state.     

A membrane-carrier mechanism for generating new sources and sinks within gradient-controlled tissues—Its application to regeneration in Oncopeltus

A model is presented that can, in principle, generate new sources and sinks within an existing gradient in the concentration of a morphogen. The novel and crucial feature of the model is that morphogens are transported between cells by membrane-based carrier molecules and not by diffusion. A further aspect of the model is the presence of a second substance within each cell whose concentration is uniform over the tissue; this molecule binds to but is not transported by the carrier and is therefore a competitive inhibitor of the morphogen. The concentration of free inhibitor in a cell determines its fate: if at any time it exceeds some threshold, that cell becomes a morphogen source; if it falls below a second threshold, the cell becomes a sink; in between them, the cell shows no special properties. Provided that differences in morphogen concentration between adjacent cells are not too great, the mechanism is indistinguishable from a normal, diffusion gradient. Examination of the kinetics of the system over a one-dimensional line of cells, however, shows that any stable morphogen difference leads to a carrier imbalance and to a change in the degree of inhibitor binding. If this difference is sufficiently great and if there is morphogen homostasis in each cell, then the free inhibitor concentration in the high morphogen cell may exceed the higher threshold causing it to become a source while the low morphogen cell becomes a sink.A numerical example of the mechanism is given and the results calculated for two-dimensional cellular arrays on either side of a morphogen discontinuity. The predictions match the observations of Wright & Lawrence (1981a, b) on Oncopeltus. These authors showed that, if pieces of epidermis from sufficiently different positions were grafted together in vivo, an ectopic boundary would form with regions of reversed polarity on either side of the join. The ability of the model to explain the regeneration and axial graft observations on hydra is also discussed and some experiments that might test the model are put forward. It is suggested that the significance of the membrane-carrier mechanism in vivo is twofold: first, to interpret the basic segmentation mechanism in embryogenesis by turning its morphogen discontinuities into source-sink pairs and so generating actual boundaries; second, to act as a homeostatic mechanism in later development, thus ensuring the maintenance of boundaries.     

Export quality: the historical bloc,state of exception,and the hegemonic process in the avocado enclave of Michoacán

Dialectical Anthropology - In this article, we offer an ethnographic and historical analysis of the avocado enclave of Michoacán, Mexico, from a Gramscian theoretical perspective. The apparent...     

The influence of light quality on C4 photosynthesis under steady-state conditions in Zea mays and Miscanthus×giganteus: changes in rates of photosynthesis but not the efficiency of the CO2 concentrating mechanism

Differences in light quality penetration within a leaf and absorption by the photosystems alter rates of CO₂ assimilation in C₃ plants. It is also expected that light quality will have a profound impact on C₄ photosynthesis due to disrupted coordination of the C₄ and C₃ cycles. To test this hypothesis, we measured leaf gas exchange, ¹³CO₂ discrimination (Δ¹³C), photosynthetic metabolite pools and Rubisco activation state in Zea mays and Miscanthus × giganteus under steady‐state red, green, blue and white light. Photosynthetic rates, quantum yield of CO₂ assimilation, and maximum phosphoenolpyruvate carboxylase activity were significantly lower under blue light than white, red and green light in both species. However, similar leakiness under all light treatments suggests the C₄ and C₃ cycles were coordinated to maintain the photosynthetic efficiency. Measurements of photosynthetic metabolite pools also suggest coordination of C₄ and C₃ cycles across light treatments. The energy limitation under blue light affected both C₄ and C₃ cycles, as we observed a reduction in C₄ pumping of CO₂ into bundle‐sheath cells and a limitation in the conversion of C₃ metabolite phosphoglycerate to triose phosphate. Overall, light quality affects rates of CO₂ assimilation, but not the efficiency of CO₂ concentrating mechanism.     

Photochemical metabolism and fruit quality of Ubá mango tree exposed to combined light and heat stress in the field

Several experiments have highlighted the complexity of stress interactions, in field conditions, involved in plant response. However, these impacts on the mechanisms involved in plant photosynthetic response remains understudied. The aim of this work was to compare the photosynthetic efficiencies and fruit quality of mango tree (Mangifera indica L.) cv. Ubá harvested from plants cultivated on the east and west sides of a commercial orchard, according to the position of plants in relation to sunrise. Chlorophyll a fluorescence, was analyzed in leaves in four different periods: fruit growth phase, fruit ripening phase, post-harvest period and after plant pruning. Photoinhibitory damage was detected by the trapped energy flux and transported electron flux per reaction center during the fruit ripening phase, and by specific energy fluxes and yield quantum efficiency after plant pruning. Although high radiation caused photoinhibition on leaves from plants cultivated on the west side of the orchard, it provided sweeter fruits. In contrast to our initial hypothesis, it was verified that plants cultivated on the west side of the orchard presented better photochemical performance in periods with the greatest requirements of photoassimilates. In addition, plants demonstrated different abilities to deal with changes on photosynthetic active radiation and high temperature. This information suggests that the phenotypic plasticity of the Ubá mango cultivar is considerable, which can be exploited to be used in regions with great relief variations and the combination of increased irradiance and high temperature.     

Distribution of 103Ru—chloride in tumor-bearing animals and the mechanism for accumulation in tumor and liver

Tumor uptake rates of ¹⁰³Ru—chloride were smaller than those for ⁶⁷Ga—citrate. In three tumors and liver, ¹⁰³Ru in the mitochondrial fraction containing lysosome increased with time after the administration of ¹⁰³Ru—chloride. The concentration of ¹⁰³Ru was more dominant in connective tissue (especially inflammatory tissue) than in viable tumor tissue or in necrotic tissue. Quite large amounts of ¹⁰³Ru in the tumor and liver were bound to the acid mucopolysaccharide whose molecular masses exceeded 40,000. Behavior of this nuclide was essentially similar to that of ⁶⁷Ga.     

Regulation of the mechanism for HCO 3 − use by the inorganic carbon level in Porphyra leucosticta Thur. in Le Jolis (Rhodophyta)

The capacity for HCO₃ ⁻ use by Porphyra leucosticta Thur. in Le Jolis grown at different concentrations of inorganic carbon (C_i) was investigated. The use of HCO₃ ⁻ at alkaline pH by P. leucosticta was␣demonstrated by comparing the O₂ evolution rates measured with the O₂ evolution rates theoretically supported by the CO₂ spontaneously formed from HCO₃ ⁻ . Both external and internal carbonic anhydrase (CA; EC 4.2.1.1) were implied in HCO₃ ⁻ use during photosynthesis because O₂ evolution rates and the increasing pH during photosynthesis were inhibited in the presence of azetazolamide and ethoxyzolamide (inhibitors for external and total CA respectively). Both external and internal CA were regulated by the C_i level at which the algae were grown. A high C_i level produced a reduction in total CA activity and a low C_i level produced an increase in total CA activity. In contrast, external CA was increased at low C_i although it was not affected at high C_i . Parallel to the reduction in total CA activity at high C_i is a reduction in the affinity for C_i, as estimated from photosynthesis versus C_i curves, was found. However, there was no evident relationship between external CA activity and the capacity for HCO₃ ⁻ use because the presence of external CA became redundant when P. leucosticta was cultivated at high C_i. Our results suggest that the system for HCO₃ ⁻ use in P. leucosticta is composed of different elements that can be activated or inactivated separately. Two complementary hypotheses are postulated: (i) internal CA is an absolute requirement for a functioning C_i-accumulation mechanism; (ii) there is a CO₂ transporter that works in association with external CA. Received: 20 April 1996 / Accepted: 5 August 1996     

Tools for living—A personal view of new status for aids for the disabled in society

Tools for Living is a concept which regards a technical aid for a disabled individual as being no different in principle from a tool which allows a normal individual to carry out a task for which his intrinsic biological equipment is inadequate.Acceptance of this concept would change the status, mechanism for provision and attitude towards technical aids, in a direction which would lower the barriers against personal acceptance, particularly in the elderly. It is forecast that the production of ‘tools’ specifically devised to compensate for the performance decrements in the elderly could become an important new branch of industry.