Near surface nutrient and phytoplankton distribution in the Drake Passage during early December

Summary Nutrient concentrations and phytoplankton species composition in near surface samples were studied along a S-N gradient in the Drake Passage, in early December 1984. Nitrate concentrations were much lower than usually previously reported from circum-Antarctic waters. Comparison of dissolved nutrient concentrations with growth requirements of Antarctic plankton algae suggests potential limitation of at least some species by nitrate or silicate. The taxonomic composition of the phytoplankton in our samples seemed to be partially controlled by competition for limiting nutrients.     

The distribution of tenascin coincides with pathways of neural crest cell migration

The distribution of the extracellular matrix (ECM) glycoprotein, tenascin, has been compared with that of fibronectin in neural crest migration pathways of Xenopus laevis, quail and rat embryos. In all species studied, the distribution of tenascin, examined by immunohistochemistry, was more closely correlated with pathways of migration than that of fibronectin, which is known to be important for neural crest migration. In Xenopus laevis embryos, anti-tenascin stained the dorsal fin matrix and ECM along the ventral route of migration, but not the ECM found laterally between the ectoderma and somites where neural crest cells do not migrate. In quail embryos, the appearance of tenascin in neural crest pathways was well correlated with the anterior-to-posterior wave of migration. The distribution of tenascin within somites was compared with that of the neural crest marker, HNK-1, in quail embryos. In the dorsal halves of quail somites which contained migrating neural crest cells, the predominant tenascin staining was in the anterior halves of the somites, codistributed with the migrating cells. In rat embryos, tenascin was detectable in the somites only in the anterior halves. Tenascin was not detectable in the matrix of cultured quail neural crest cells, but was in the matrix surrounding somite and notochord cells in vitro. Neural crest cells cultured on a substratum of tenascin did not spread and were rounded. We propose that tenascin is an important factor controlling neural crest morphogenesis, perhaps by modifying the interaction of neural crest cells with fibronectin.     

The distribution of fibronectin and tenascin along migratory pathways of the neural crest in the trunk of amphibian embryos

It is generally assumed that in amphibian embryos neural crest cells migrate dorsally, where they form the mesenchyme of the dorsal fin, laterally (between somites and epidermis), where they give rise to pigment cells, and ventromedially (between somites and neural tube), where they form the elements of the peripheral nervous system. While there is agreement about the crest migratory routes in the axolotl (Ambystoma mexicanum), different opinions exist about the lateral pathway in Xenopus. We investigated neural crest cell migration in Xenopus (stages 23, 32, 35/36 and 41) using the X. laevis-X. borealis nuclear marker system and could not find evidence for cells migrating laterally. We have also used immunohistochemistry to study the distribution of the extracellular matrix (ECM) glycoproteins fibronectin (FN) and tenascin (TN), which have been implicated in directing neural crest cells during their migrations in avian and mammalian embryos, in the neural crest migratory pathways of Xenopus and the axolotl. In premigratory stages of the crest, both in Xenopus (stage 22) and the axolotl (stage 25), FN was found subepidermally and in extracellular spaces around the neural tube, notochord and somites. The staining was particularly intense in the dorsal part of the embryo, but it was also present along the visceral and parietal layers of the lateral plate mesoderm. TN, in contrast, was found only in the anterior trunk mesoderm in Xenopus; in the axolotl, it was absent. During neural crest cell migration in Xenopus (stages 25-33) and the axolotl (stages 28-35), anti-FN stained the ECM throughout the embryo, whereas anti-TN staining was limited to dorsal regions. There it was particularly intense medially, i.e. in the dorsal fin, around the neural tube, notochord, dorsal aorta and at the medial surface of the somites (stage 35 in both species). During postmigratory stages in Xenopus (stage 40), anti-FN staining was less intense than anti-TN staining. In culture, axolotl neural crest cells spread differently on FN- and TN-coated substrata. On TN, the onset of cellular outgrowth was delayed for about 1 day, but after 3 days the extent of outgrowth was indistinguishable from cultures grown on FN. However, neural crest cells in 3-day-old cultures were much more flattened on FN than on TN. We conclude that both FN and TN are present in the ECM that lines the neural crest migratory pathways of amphibian embryos at the time when the neural crest cells are actively migrating. FN is present in the embryonic ECM before the onset of neural crest migration.(ABSTRACT TRUNCATED AT 400 WORDS)     

Loss of Cytosolic Phosphoglucose Isomerase Affects Carbohydrate Metabolism in Leaves and Is Essential for Fertility of Arabidopsis

Carbohydrate metabolism in plants is tightly linked to photosynthesis and is essential for energy and carbon skeleton supply of the entire organism. Thus, the hexose phosphate pools of the cytosol and the chloroplast represent important metabolic resources that are maintained through action of phosphoglucose isomerase (PGI) and phosphoglucose mutase interconverting glucose 6-phosphate, fructose 6-phosphate, and glucose 1-phosphate. Here, we investigated the impact of disrupted cytosolic PGI (cPGI) function on plant viability and metabolism. Overexpressing an artificial microRNA targeted against cPGI (amiR-cpgi) resulted in adult plants with vegetative tissue essentially free of cPGI activity. These plants displayed diminished growth compared with the wild type and accumulated excess starch in chloroplasts but maintained low sucrose content in leaves at the end of the night. Moreover, amiR-cpgi plants exhibited increased nonphotochemical chlorophyll a quenching during photosynthesis. In contrast to amiR-cpgi plants, viable transfer DNA insertion mutants disrupted in cPGI function could only be identified as heterozygous individuals. However, homozygous transfer DNA insertion mutants could be isolated among plants ectopically expressing cPGI. Intriguingly, these plants were only fertile when expression was driven by the ubiquitin10 promoter but sterile when the seed-specific unknown seed protein promoter or the Cauliflower mosaic virus 35S promoter were employed. These data show that metabolism is apparently able to compensate for missing cPGI activity in adult amiR-cpgi plants and indicate an essential function for cPGI in plant reproduction. Moreover, our data suggest a feedback regulation in amiR-cpgi plants that fine-tunes cytosolic sucrose metabolism with plastidic starch turnover.Starch and Suc turnover are major pathways of primary metabolism in all higher plants. As such, they are essential for carbohydrate storage and the energy supply of sink tissues and as building blocks for amino acid, fatty acid, or cell wall biosynthesis (Stitt and Zeeman, 2012).A core reaction in both starch and Suc biosynthesis is the reversible interconversion of the hexose phosphate pool metabolites Fru 6-phosphate (Fru6P) and Glc 6-phosphate (Glc6P), which is mediated by phosphoglucose isomerase (PGI). Arabidopsis (Arabidopsis thaliana) contains two isoforms of PGI, one in the plastids and one in the cytosol (Caspar et al., 1985).During the light period, the plastid isoform of PGI (PGI1) is involved in starch biosynthesis by generating Glc6P from the primary photosynthetic product Fru6P. Glc6P is further converted to Glc 1-phosphate (Glc1P) and ADP-glucose via action of phosphoglucomutase (PGM) and ADP-glucose pyrophosphorylase (AGPase), respectively (Stitt and Zeeman, 2012). Finally, transfer of the glucosyl moiety of ADP-glucose to the growing carbohydrate chain of starch is mediated by starch synthases. Any of the enzymatic reactions of this linear pathway is essential for starch synthesis, as illustrated by the virtual absence of transitory starch in chloroplasts of mutant plant lines with impaired function of PGI1 (Yu et al., 2000; Kunz et al., 2010), PGM (Caspar et al., 1985; Kofler et al., 2000), or AGPase (Lin et al., 1988). Interestingly, in a few specific cell types, e.g. leaf guard cells and root columella cells, loss of PGI1 activity can be bypassed by the presence of the plastid Glc6P/phosphate translocator GPT1 (Niewiadomski et al., 2005; Kunz et al., 2010).The cytosolic isoform of PGI (cPGI) is involved in anabolism and catabolism of Suc, the major transport form of carbohydrates in plants. Glc6P and Fru6P interconversion is necessary for both Suc synthesis during the day and during the night. During the day, Suc synthesis in source leaves is fueled mainly by triose phosphates exported from chloroplasts that are eventually converted to Fru6P in the cytosol. However, Fru6P is only one substrate for the Suc-generating enzyme Suc phosphate synthase. The second substrate, UDP-glucose, is synthesized from Fru6P via Glc6P and Glc1P by the cytosolic isoenzymes of PGI1 and PGM as well as UDP-glucose pyrophosphorylase.Because Suc is the major long-distance carbon transport form, its synthesis has to continue throughout the night to supply energy and carbohydrates to all tissues. The nocturnal synthesis of Suc is dependent on breakdown and mobilization of transitory starch from chloroplasts (Zeeman et al., 2007) via export of maltose and Glc (Weber et al., 2000; Niittylä et al., 2004; Weise et al., 2004; Cho et al., 2011). Exported maltose is temporarily integrated into cytosolic heteroglycans (Fettke et al., 2005) mediated by disproportionating enzyme2 (DPE2; Chia et al., 2004; Lu and Sharkey, 2004) yielding Glc and a heteroglycan molecule elongated by an α1-4-bound glucosyl residue. Cytosolic Glc can directly be phosphorylated to Glc6P by the action of hexokinase, while temporarily stored Glc in heteroglycans is released as Glc1P mediated by cytosolic glucan phosphorylase2 (PHS2; Fettke et al., 2004; Lu et al., 2006). Both Glc6P and Glc1P can then be converted to UDP-glucose as during the day.Generation of Fru6P, the second substrate for Suc synthesis, can proceed only to a limited extent from triose phosphates during the night. This limitation is caused mainly by the nocturnal inactivation of Fru 1,6-bisphosphatase (Cséke et al., 1982; Stitt, 1990), a key enzyme in Suc biosynthesis during the day. Hence, in contrast to the situation in the light, cPGI activity is now crucial for providing Fru6P from Glc6P.On the catabolic side, degradation of Suc into its monosaccharides in sink tissues yields both Glc6P and Fru6P, of which only Fru6P can be utilized in glycolytic degradation. Therefore, cPGI is also required for Glc6P conversion to Fru6P in glycolysis, which, in combination with respiration, is the major path of energy production in heterotrophic tissues.Impairment or loss of function of enzymes contributing to the cytosolic hexose phosphate pool has recently been investigated for the Glc1P-forming enzyme PGM (Egli et al., 2010). The Arabidopsis genome encodes three PGM isoforms, with PGM1 localized to plastids and PGM2 and PGM3 localized to the cytosol (Caspar et al., 1985; Egli et al., 2010). Analyses of transfer DNA (T-DNA) mutants showed that homozygous pgm2/pgm3 double mutants were nonviable because of impaired gametophyte development. However, pgm2 and pgm3 single mutants grew like ecotype Columbia (Col-0) wild-type plants, indicating overlapping functions of PGM2 and PGM3 (Egli et al., 2010).By contrast, cPGI is encoded only by a single locus in Arabidopsis (Kawabe et al., 2000). Higher plant mutants reduced in cPGI activity have so far been characterized only in ethyl methanesulfonate-mutagenized Clarkia xantiana (Jones et al., 1986a; Kruckeberg et al., 1989; Neuhaus et al., 1989). The C. xantiana genome encodes for two isoenzymes of cPGI, and homozygous point mutations in each individual cPGI led to significant decrease in cPGI enzyme activity, which was further reduced to a residual activity of 18% in cpgi2/cpgi3 double mutants, where the cPGI3 locus was heterozygous for the mutation (Jones et al., 1986a; Kruckeberg et al., 1989). Detailed physiological analyses of these mutants indicated a negative impact on Suc biosynthesis and elevated starch levels when cPGI activity was decreased at least 3- to 5-fold (Kruckeberg et al., 1989).The physiological impact of decreased or even absent cPGI activity has not been characterized in the genetic model organism Arabidopsis. Here, we show that homozygous T-DNA insertion mutants in the cPGI locus are nonviable and present data from analyses of mature Arabidopsis plants constitutively expressing artificial microRNAs (amiRNAs) targeted against cPGI. These mutants reveal altered photosynthesis, a strong impact on nocturnal leaf starch degradation, and impaired Suc metabolism.     

Improvement of microcirculation after percutaneous transluminal angioplasty in the lower limb with prostaglandin E1

OBJECTIVE: The aim of the study was to investigate prospectively the microcirculation after angioplasty and its improvement with additional Prostaglandin E1 (PGE1) therapy assessed by transcutaneous pressure of oxygen. PATIENTS AND METHODS: 45 patients with intermittent claudication eligible for angioplasty were enrolled in a prospective randomised controlled clinical trial. Patients received either intra-arterial bolus of 40 microg PGE1 in addition to angioplasty or a 40 microg PGE1 intravenous infusion. Control group received no trial medication. Additional 15 patients undergoing intra-arterial angiography were also investigated. tcpO(2) values were recorded distal to the PTA region before, during the intervention, 24h, 2 and 4 weeks after intervention. Clinical endpoint was the change of tcpO(2) values 4 weeks after intervention. RESULTS: During the 4 week follow-up tcpO(2) values decreased in patients treated with angioplasty. At the same time tcpO(2) increased significantly in those patients additionally treated with intra-arterial PGE1 bolus injection as well as with intravenous PGE1 infusion. CONCLUSIONS: Impaired microcirculation after angioplasty can be improved with additional intravenous as well as intra-arterial PGE1 administration.     

Nocturnal energy demand in plants: Insights from studying mutants impaired in β-oxidation

All photosynthetic organisms face the difficulty of maintaining cellular metabolism in the absence of photosynthetic active radiation during the night. Although many consuming metabolic pathways (e.g., fatty acid synthesis) are only active in the light, plant cells still require basic levels of metabolic energy and reductive power during the night for sustained growth and development.Key words: PXA1, comatose, β-oxidation, fatty acids, starch, imaging PAM, extended darkness     

Reduction of the Cytosolic Phosphoglucomutase in Arabidopsis Reveals Impact on Plant Growth,Seed and Root Development,and Carbohydrate Partitioning

Phosphoglucomutase (PGM) catalyses the interconversion of glucose 1-phosphate (G1P) and glucose 6-phosphate (G6P) and exists as plastidial (pPGM) and cytosolic (cPGM) isoforms. The plastidial isoform is essential for transitory starch synthesis in chloroplasts of leaves, whereas the cytosolic counterpart is essential for glucose phosphate partitioning and, therefore, for syntheses of sucrose and cell wall components. In Arabidopsis two cytosolic isoforms (PGM2 and PGM3) exist. Both PGM2 and PGM3 are redundant in function as single mutants reveal only small or no alterations compared to wild type with respect to plant primary metabolism. So far, there are no reports of Arabidopsis plants lacking the entire cPGM or total PGM activity, respectively. Therefore, amiRNA transgenic plants were generated and used for analyses of various parameters such as growth, development, and starch metabolism. The lack of the entire cPGM activity resulted in a strongly reduced growth revealed by decreased rosette fresh weight, shorter roots, and reduced seed production compared to wild type. By contrast content of starch, sucrose, maltose and cell wall components were significantly increased. The lack of both cPGM and pPGM activities in Arabidopsis resulted in dwarf growth, prematurely die off, and inability to develop a functional inflorescence. The combined results are discussed in comparison to potato, the only described mutant with lack of total PGM activity.     

The acyl-acyl carrier protein synthetase from Synechocystis sp. PCC 6803 mediates fatty acid import

The transfer of fatty acids across biological membranes is a largely uncharacterized process, although it is essential at membranes of several higher plant organelles like chloroplasts, peroxisomes, or the endoplasmic reticulum. Here, we analyzed loss-of-function mutants of the unicellular cyanobacterium Synechocystis sp. PCC 6803 as a model system to circumvent redundancy problems encountered in eukaryotic organisms. Cells deficient in the only cytoplasmic Synechocystis acyl-acyl carrier protein synthetase (SynAas) were highly resistant to externally provided α-linolenic acid, whereas wild-type cells bleached upon this treatment. Bleaching of wild-type cells was accompanied by a continuous increase of α-linolenic acid in total lipids, whereas no such accumulation could be observed in SynAas-deficient cells (Δsynaas). When SynAas was disrupted in the tocopherol-deficient, α-linolenic acid-hypersensitive Synechocystis mutant Δslr1736, double mutant cells displayed the same resistance phenotype as Δsynaas. Moreover, heterologous expression of SynAas in yeast (Saccharomyces cerevisiae) mutants lacking the major yeast fatty acid import protein Fat1p (Δfat1) led to the restoration of wild-type sensitivity against exogenous α-linolenic acid of the otherwise resistant Δfat1 mutant, indicating that SynAas is functionally equivalent to Fat1p. In addition, liposome assays provided direct evidence for the ability of purified SynAas protein to mediate α-[(14)C]linolenic acid retrieval from preloaded liposome membranes via the synthesis of [(14)C]linolenoyl-acyl carrier protein. Taken together, our data show that an acyl-activating enzyme like SynAas is necessary and sufficient to mediate the transfer of fatty acids across a biological membrane.