Polyommatus ripartii is a biogeographically and taxonomically poorly understood species of butterfly with a scattered distribution in Europe. Recently, it has been shown that this species includes several European endemic and localized taxa (galloi, exuberans, agenjoi) that were previously considered species and even protected, a result that poses further questions about the processes that led to its current distribution. We analysed mitochondrial DNA and the morphology of P. ripartii specimens to study the phylogeography of European populations. Three genetically differentiated but apparently synmorphic lineages occur in Europe that could be considered evolutionarily significant units for conservation. Their strongly fragmented and counterintuitive distribution seems to be the result of multiple range expansions and contractions along Pleistocene climatic oscillations. Remarkably, based on the 79 specimens studied, these genetic lineages do not seem to extensively coexist in the distributional mosaic, a phenomenon most evident in the Iberian Peninsula. One of the important gaps in the European distribution of P. ripartii is reduced by the discovery of new Croatian populations, which also facilitate a better understanding of the biogeography of the species.
Summary The aim of this work was to quantify the contribution of isocitrate lyase to the control of gluconeogenesis in endosperm from 4‐day‐old castor bean seedlings. The approach was based on metabolic control analysis following selective inhibition of enzyme activity. Both 3‐nitropropionate and itaconate decreased the proportion of either [1‐14C]acetate or [2‐14C]acetate converted to sucrose, and increased the proportion metabolized through the tricarboxylic acid cycle. Kinetic analysis of isocitrate lyase activity from endosperm revealed that itaconate is a pure uncompetitive inhibitor (Ki′ = 11.9 ±0.98 μm) with respect to isocitrate. In contrast, 3‐nitropropionate is a slow, tight‐binding inhibitor. The half‐time for inhibition of isocitrate lyase by 3‐nitropropionate was 5–10 min, whereas the half‐time for reactivation was in excess of 10 h. Incubating endosperm in 3‐nitropropionate resulted in a concentration‐dependent decrease in isocitrate lyase activity that remained stable in tissue extracts for at least 4 h. From a comparison of the extent of in situ inactivation of isocitrate lyase by 3‐nitropropionate and the effect of this compound on the rate of sucrose production from [2‐14C]acetate, the flux control coefficient of isocitrate lyase on gluconeogenesis from acetate in castor bean endosperm was calculated to be 0.66 ± 0.09. It is concluded that isocitrate lyase activity is quantitatively important in the control of gluconeogenic flux, and suggested that developmental changes in the amount of this enzyme may be an important factor in determining the conversion of lipid to sugar in young castor bean seedlings.
Summary In most higher plants, chloroplasts move towards the periclinal cell walls in weak blue light (WBL) to increase light harvesting for photosynthesis, and towards the anticlinal walls as an escape reaction, thus avoiding photo‐damage in strong blue light (SBL). The photo‐ receptor(s) triggering these responses have not yet been identified. In this study, the role of zeaxanthin as a blue‐light photoreceptor in chloroplast movements was investigated. Time‐lapse 3D confocal imaging in Lemna trisulca showed that individual chloroplasts responded to local illumination when one half of the cell was treated with light of different intensity or spectral quality to that received by the other half, or was maintained in darkness. Thus the complete signal perception, transduction and effector system has a high degree of spatial resolution and is consistent with localization of part of the transduction chain in the chloroplasts. Turnover of xanthophylls was determined using HPLC, and a parallel increase was observed between zeaxanthin and chloroplast movements in SBL. Ascorbate stimulated both a transient increase in zeaxanthin levels and chloroplast movement to profile in physiological darkness. Conversely, dithiothreitol blocked zeaxanthin production and responses to SBL and, to a lesser extent, WBL. Norflurazon preferentially inhibited SBL‐dependent chloroplast movements. Increases in zeaxanthin were also observed in strong red light (SRL) when no directional chloroplast movements occurred. Thus it appears that a combination of zeaxanthin and blue light is required to trigger responses. Blue light can cause cis–trans isomerization of xanthophylls, thus photo‐isomerization may be a critical link in the signal transduction pathway.
Bovine brains contain large amounts of isoprenoid compounds and the enzymes involved in their biosynthesis were investigated. Ten different regions were dissected from fresh bovine brains and, in addition, fractions from cerebellum, spinal cord, and hypophysis were obtained. The cholesterol concentration was found to be ∼8 mg/g in the cortex regions and three times higher in the pons, medulla oblongata, and white matter. Dolichol concentration varied between 8 and 40 µg/g in the different tissues, and ubiquinone was found at a lower level, which varied between 3 and 25 µg/g. Farnesyl‐pyrophosphate synthase activity in cytosolic fractions from various regions exhibited only a twofold variation, whereas geranylgeranyl pyrophosphate synthase displayed larger differences, being particularly rich in the pons, medulla oblongata, white matter, and spinal cord. Squalene synthase activity was lowest in the thalamus and threefold higher in the pons. Determination of specific activity based on cholesterol content revealed that enzyme activities in various regions are not related to the actual lipid amount present. Both cis‐ and trans‐prenyltransferases exhibited similarities in their regional distribution showing up to 20‐fold differences in activity. Thus, it appears that the mevalonate pathway lipids and the various branch point enzymes involved in their syntheses vary greatly in different brain regions and are subjected to separate regulation.
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