β-Carotene, vitamin C and vitamin E content of the marine microalga Dunaliella tertiolecta cultured with different nitrogen sources

Variations in the β-carotene, vitamin C and vitamin E content of D. tertiolecta have been shown to result from the nitrogen source used in the culture medium. Differences of 101%, 38% and 69% have been found in β-carotene, ascorbic acid and tocopherol content in mg/g of dry matter, respectively, and differences of 147%, 63% and 37% occurred in β-carotene, vitamin C and E concentrations in mg/litre of culture, respectively. Considering the β-carotene, vitamin C and vitamin E content in mg/g of chlorophyll a, maximum variations occurred in β-carotene content, with differences of 145% among the different nitrogen sources. Maximum β-carotene and vitamin C values were found in urea cultures, whereas urea cultures showed the minimum values for vitamin E.     

Heteronarce rierai,a new narkid ray from Mozambique,western Indian ocean

Heteronarce rierai sp. nov. is described on the basis of six specimens, one male and five females, caught in the waters off Mozambique (western Indian Ocean). Total lengths range from 257 to 296 mm. The new species is distinguished from the three other species of the genusHeteronarce by its narrower disc width (29.6% of TL in male, and 33.0 to 39.2% of TL in females), shorter disc length (32.7% of TL in male, and 34.4 to 40.6% of TL in females), and its longer interdorsal distance (10.1 to 11.7% of TL).     

Inhibition of Brain Glutamate Decarboxylase Activity Is Related to Febrile Seizures in Rat Pups

Because previous work showed that in the newborn brain, but not in the adult brain, glutamate decarboxylase (GAD) is notably susceptible to heat, we have studied the possible involvement of GAD inhibition in febrile convulsions and the related changes in gamma-aminobutyric acid (GABA) content. Rats of different ages were subjected to hyperthermia, and GAD activity was determined in brain homogenates by measuring the release of 14CO2 from labeled glutamate and by measuring the formation of GABA. The latter method gave considerably lower values than the former in the youngest rats, and was considered more reliable. With this method, we found a 37-48% inhibition of GAD activity in rat pups 2-5 days old, which showed febrile seizures at progressively higher body temperatures, whereas in 10- and 15-day-old animals, which did not show convulsions, GAD activity was not affected by hyperthermia. Whole-brain GABA levels, however, did not change at any age. In contrast to GAD, choline acetyltransferase and lactic dehydrogenase activities were not altered by hyperthermia at any of the ages studied. These results suggest that a decreased efficiency of the inhibitory neurotransmission mediated by GABA, consequent to the inhibition of GAD activity, may be a factor related to febrile convulsions.     

Fine-root biomass and soil properties in a semideciduous and a lower montane rain forest in Panama

The distribution of root biomass and physical and chemical properties of the soils were studied in a semideciduous and in a lower montane rain forest in Panama. Roots and soil samples were taken by means of soil cores (25 cm deep) and divided into five, 5-cm deep sections. Soils were wet-sieved to retrieve the roots that were classified in four diameter classes: very fine roots (<1 mm), fine roots (1–2 mm), medium roots (2–5 mm) and coarse roots (5–50 mm). Soil samples were analyzed for organic carbon, total nitrogen, available phosphorus, exchangeable bases, cation exchange capacity, pH, aluminium and exchangeable acidity. Total root biomass measured with the soil corer (roots <50 mm in diameter) was not different between the forests (9.45 t ha^-1), while biomass of very fine roots was larger in the mountains (2.00 t ha^-1) than in the lowlands (1.44 t ha^-1). The soils in the semideciduous forest were low in available phosphorus, while in the mountains, soils had low pH, high exchangeable aluminium and exchangeable acidity, and low concentration of exchangeable bases. Phosphorus was in high concentration only in the first 5 cm of the soil. In both forests, there was an exponential reduction of root biomass with increasing depth, and most of the variation in the vertical distribution of roots less than 2 mm in diameter was explained by the concentration of nitrogen in the soils. The results of this study support the hypothesis that a large root biomass in montane forests is related to nutrients in low concentration and diluted in organic soils with high CEC and low bulk density, and that fine root biomass in tropical forests in inversely related to calcium availability but not a phosphorus as has been suggested for other forests.     

Dark inhibition of ribulose-1,5-bisphosphate carboxylase/oxygenase in legumes: A biosystematic study

2-carboxyarabinitol 1-phosphate (CA 1-P) is a naturally occurring inhibitor of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Members of the Fabaceae exhibit a particularly wide range in the extent of CA 1-P accumulation during darkness and include Phaseolus vulgaris, whose dark/light regulation of Rubisco activity is principally achieved by synthesis/degradation of CA 1-P. An extensive survey of the degree of dark inhibition of Rubisco was undertaken for the subfamily Papilionoideae to elucidate evolutionary patterns in the occurrence of this regulatory mechanism. Seventy-five species from 21 tribes were examined. Dark inhibition of Rubisco was found in ancestral tribes such as the Sophoreae, but was substantially reduced or absent in representative species of three more recently evolved tribes, Cicereae, Hedysareae and Vicieae. We conclude that regulation of Rubisco by CA 1-P is neither of recent origin nor of restricted distribution among the Papilionoideae. On the contrary, it becomes lost or less pronounced only in a minority of the more evolutionarily advanced species in this important subfamily.     

Conditions for selective degradation of lignin by the fungus Ganoderma australis

Summary The white-rot fungus Ganoderma australis selectively degrades lignin in the ecosystem palo podrido. Using conditions that simulate those of palo podrido in the laboratory, it was found that low nitrogen content and low O₂ tension stimulate the productio of manganese peroxidase and lignin degradation, and depress cellulose degradation and cellulase production. The inverse is found at high nitrogen concentration and high O₂ tension. This agrees with previous results indicating that low O₂ tension and low nitrogen stimulate selective lignin degradation by this fungus. Correspondence to: J. Eyzaguirre     

Translational efficiency of mRNA in yeast cells is not increased by plant viral leader sequences

Summary Synthetic oligonucleotides encoding the 5-non-translated (leader) sequence of the coat protein mRNA of alfalfa mosaic virus RNA 4 or the leader sequence of tobacco mosaic virus RNA were used to replace the natural leader region of the yeast phosphoglycerate kinase (PGK1) mRNAs and the translational efficiency of the chimeric mRNA was determined in yeast cells. In neither case did we observed a significant increase compared to the translational efficiency shown by the wild-type PGK mRNA, in contrast to the known stimulatory effect of these leader sequences on translation in mammalian, plant and bacterial in-vivo and/or in-vitro systems. The same result was obtained when the translational efficiencies in yeast cells of Escherichia coli -galactosidase mRNAs carrying the PGK or either of the two viral leader sequences were compared. Offprint requests to: H. A. Raué     

Enhanced glucan formation of filamentous fungi by effective mixing,oxygen limitation and fed-batch processing

Summary Glucan formation ofSchizophyllum commune andSclerotium glucanicum were investigated. Process data obtained during batch cultivation are presented. Glucan release can be improved by oxygen limitation. Thus, growth and glucan release are influenced by oxygen in opposite ways. Possible pathways of this oxygen-dependent regulation are discussed. A draft-tube/propeller system, rushtonturbine-, fan- and helicon-ribbon-impeller as well as a fundaspi and intermig agitator were tested. The 4-bladed fan impeller withd ^*=0.64 yielded the best results, since effective bulk mixing is much more important than bubble break up (micromixing) with regard to this system. Fed-batch cultivation always resulted in higher rates of glucan formation than the batch process.     

In vivo and in vitro analysis of structure-function relationships in ribosomal protein L25 from Saccharomyces cerevisiae

We have developed a combination of in vivo and in vitro methods which allows us to determine the effect of practically every structural change, deletions as well as point mutations, on various biological functions of a ribosomal protein (r-protein). We have used this approach to delineate the functional domains of r-protein L25 from Saccharomyces cerevisiae. By analysis of the intracellular distribution of fusion proteins carrying various portions of L25 linked to Escherichia coli beta-galactosidase we traced the nuclear localization signal(s) of L25 to the region encompassing the N-terminal 61 amino acids of the protein. On the other hand, using in vitro prepared fragments of L25 we located the domain responsible for its specific binding to 26S rRNA to the region between amino acids 61 and 135. In order to be able to analyze the effect of mutations in L25 on ribosome biogenesis and function in vivo we constructed a mutant yeast strain in which the chromosomal L25 gene is placed under control of the inducible yeast GAL promoter. Since this strain is unable to grow on glucose as a carbon source the L25 gene must be essential for cell viability. Growth on glucose can be restored by introduction of a wild-type L25 gene on a plasmid, demonstrating that under these conditions the cells are dependent upon an extrachromosomally supplied copy of the gene.     

INFLORESCENCE SIZE AND FRUIT DISTRIBUTION AMONG INDIVIDUALS IN THREE ORCHID SPECIES

Fruit distribution among individuals in populations of three orchid species was analyzed. Fruit set was low in the three species. The distribution of fruits in the non-autogamous species was skewed to the right, with high variance: mean ratios, and a moderate to high proportion of fruitless plants. Larger inflorescence size did not necessarily result in an increase in percent fruit set but tended to increase the probability to produce at least one fruit. Pollinator-mediated selection on inflorescence size through fruit production may be limited by the low overall level of visitation and the resulting uncertainty of pollination at the individual level.