Root production and root turnover in two dominant species of wet heathlands

Summary Root biomass production, root length production and root turnover of Erica tetralix and Molinia caerulea were estimated by sequential core sampling and by observations in permanent minirhizotrons in the field. Root biomass production, estimated by core sampling, was 370 (Erica) and 1080 (Molinia) g m^-2 yr^-1. This was for both species equal to aboveground production. Assuming steady-state conditions for the root system, root biomass turnover rates (yr^-1), estimated by core sampling, were 1.72 (Erica) and 1.27 (Molinia). Root length production of both species, estimated by minirhizotron observations, varied significantly with observation depth. Root length turnover rate (yr^-1) of both species did not vary significantly with observation depth and averaged 0.92 in Erica and 2.28 in Molinia. Reasons are given for the discrepancy between the results of the two types of turnover measurements. The data suggest that the replacement of Erica by Molinia in a wet heathland, which occurs when nutrient availability increases, leads to an increased flow of carbon and nutrients into the soil-system. Therefore, there may be a positive feedback between dominance of Molinia and nutrient availability.     

Comparative study on glucocerebrosidase in spleens from patients with Gaucher disease.

In Gaucher disease (glucosylceramide lipidosis), deficiency of glucocerebrosidase causes pathological storage of glucosylceramide, particularly in the spleen. A comparative biochemical and immunological analysis has therefore been made of glucocerebrosidase in spleens from normal subjects (n = 4) and from Gaucher disease patients with non-neuronopathic (n = 5) and neuronopathic (n = 5) phenotypes. The spleens from all Gaucher disease patients showed markedly decreased glucocerebrosidase activity. Discrimination of different phenotypes of Gaucher disease was not possible on the basis of the level of residual enzyme activity, or by measurements, using the immunopurified enzyme, of kinetic constants, pI or molecular mass forms. A severe decrease was found in the specific activity of glucocerebrosidase purified to homogeneity from the spleen of a patient with the non-neuronopathic phenotype of Gaucher disease, as compared with that of the enzyme purified from the spleen of a normal subject. This finding was confirmed by an immunological method developed for accurate assessment of the relative enzyme activity per molecule of glucocerebrosidase protein. The method revealed that the residual enzyme in the spleens of all investigated patients with a non-neuronopathic course of Gaucher disease had a more than 7-fold decreased activity of glucocerebrosidase (measured in the presence of taurocholate) per molecule of enzyme, and that the concentration of glucocerebrosidase molecules in the spleens of these patients was near normal. Observations made with immunoblotting experiments were consistent with these findings. In contrast, in the spleens of patients with neuronopathic phenotypes of Gaucher disease, the concentration of glucocerebrosidase molecules was severely decreased.     

Cyclic AMP induces a transient alkalinization in Dictyostelium

In a wide range of cell types, stimulus-response coupling is accompanied by a rise in cytoplasmic pH (pH_i). It is shown that stimulation of developing Dictyostelium discoideum cells with the chemoattractant cAMP also results in a rise in pH_i. About 1.5 min after stimulation, pH_i starts increasing from pH_i7.45 to pH_i7.60, as is revealed independently by two different pH null-point methods. The rise in pH_i is transient, also with a persistent stimulus, and effectively inhibited by diethylstilbestrol (DES), strongly suggesting that the rise in pH_i is accomplished by the DES-sensitive plasma membrane proton pump which has been demonstrated in D. discoideum.     

The endocrine pancreas during pregnancy and lactation in the rat

The percentage of endocrine tissue in the whole pancreas, the volume density of the insulin producing beta-cells, the non-fasting plasma glucose level and the plasma insulin level were studied in pregnant rats and in puerperal lactating and non-lactating rats. During pregnancy there was a progressive rise in the percentage of endocrine tissue, in the volume density of the beta-cells and in the insulin level in peripheral blood. Plasma glucose levels declined during pregnancy. A lower plasma glucose level, a lower plasma insulin level, a lower percentage of endocrine tissue and a lower volume density of the beta-cells was found in lactating compared to non-lactating rats.     

The distribution of strictosidine-synthase activity and alkaloids in Cinchona plants

The relation between the total alkaloid content and the activity of strictosidine synthase (EC 4.3.3.2), a key enzyme in alkaloid biosynthesis, was studied in distinct parts of six-month-old plants of Cinchona ledgeriana Moens. Strictosidine-synthase activity was present in the tops of the stems, including the young developing leaflets, and in the roots. The highest alkaloid contents of the plant were also found in these parts; however, the types of alkaloids differed, cinchophyllines being present in the aerial parts and quinoline alkaloids in the roots. In the stem and in old leaves, both strictosidine-synthase activity and alkaloid content were low. These results indicate that in young Cinchona plants the alkaloids are mainly synthesized in the axial extremities of the plant and that they are stored at the site of their synthesis.Abbreviations HPLC high-performance liquid chromatography - SSS strictosidine synthase We wish to thank Wim Snoeijer for excellent technical assistance, and Dr. H.J.v.d. Meulen, Multiplant Holding B.V. (Maarssen), for kindly providing us with Cinchona ledgeriana Moens seeds. Financial support by Multiplant Holding B.V. (Maarssen) is gratefully acknowledged.To whom correspondence should be addressed.     

Mannose 6-phosphate-independent targeting of cathepsin D to lysosomes in HepG2 cells.

We have studied the role of N-linked oligosaccharides and proteolytic processing on the targeting of cathepsin D to the lysosomes in the human hepatoma cell line HepG2. In the presence of tunicamycin cathepsin D was synthesized as an unglycosylated 43-kDa proenzyme which was proteolytically processed via a 39-kDa intermediate to a 28-kDa mature form. Only a small portion was secreted into the culture medium. During intracellular transport the 43-kDa procathepsin D transiently became membrane-associated independently of binding to the mannose 6-phosphate receptor. Subcellular fractionation showed that unglycosylated cathepsin D was efficiently targeted to the lysosomes via intermediate compartments similar to the enzyme in control cells. The results show that in HepG2 cells processing and transport of cathepsin D to the lysosomes is independent of mannose 6-phosphate residues. Inhibition of the proteolytic processing of 53-kDa procathepsin D by protease inhibitors caused this form to accumulate intracellularly. Subcellular fractionation revealed that the procathepsin D was transported to lysosomes, thereby losing its membrane association. Procathepsin D taken up by the mannose 6-phosphate receptor also transiently became membrane-associated, probably in the same compartment. We conclude that the mannose 6-phosphate-independent membrane-association is a transient and compartment-specific event in the transport of procathepsin D.     

L’electromyographie du penis: Une nouvelle exploration du muscle lisse caverneux et de son controle neurologique?

The authors have investigated the electrical activity of corpus cavernous, first according to Wagner and Gerstenberg’ method, then, since one year, according to Stief method, in the basal state and following intracavernosal injection of vasoactive agents, or following various stimulation tests. They have found again the electrical activity described by these authors, but have been confronted with the difficulty in quantifying the data. Specially single potential analysis seems to them little reliable and reproducible for an objective interpretation. At this stage of their experience, they test two simpler criteria interpretation: the richness of the electrical activity, and the reactivity of the recording to various stimulations. Their preminary results suggest a correlation between those criteria and the state of the autonomic nervous system of the penis.     

Complete sequences of the rRNA genes of Drosophila melanogaster

In this, the first of three papers, we present the sequence of the ribosomal RNA (rRNA) genes of Drosophila melanogaster. The gene regions of D. melanogaster rDNA encode four individual rRNAs: 18S (1,995 nt), 5.8S (123 nt), 2S (30 nt), and 28S (3,945 nt). The ribosomal DNA (rDNA) repeat of D. melanogaster is AT rich (65.9% overall), with the spacers being particularly AT rich. Analysis of DNA simplicity reveals that, in contrast to the intergenic spacer (IGS) and the external transcribed spacer (ETS), most of the rRNA gene regions have been refractory to the action of slippage-like events, with the exception of the 28S rRNA gene expansion segments. It would seem that the 28S rRNA can accommodate the products of slippage-like events without loss of activity. In the following two papers we analyze the effects of sequence divergence on the evolution of (1) the 28S gene "expansion segments" and (2) the 28S and 18S rRNA secondary structures among eukaryotic species, respectively. Our detailed analyses reveal, in addition to unequal crossing-over, (1) the involvement of slippage and biased mutation in the evolution of the rDNA multigene family and (2) the molecular coevolution of both expansion segments and the nucleotides involved with compensatory changes required to maintain secondary structures of RNA.      

Heterogeneity in human acid beta-glucosidase revealed by cellulose-acetate electrophoresis

Cellulose-acetate gel electrophoresis, a technique commonly used for the separation of human acid hydrolases, was applied to study heterogeneity in acid beta-glucosidase (EC 3.2.1.45). With this technique, three forms of beta-glucosidase were distinguishable in extracts of several tissues. The most anodic beta-glucosidase activity (band 3) represents the broad-specificity beta-glucosidase that is not deficient in Gaucher disease and is not inhibited by conduritol B-epoxide (CBE). The beta-glucosidase activity was deficient in Gaucher disease. A third beta-glucosidase activity with an intermediate mobility (band 2) was also inhibited by CBE and deficient in Gaucher disease. Band 1 and band 2 beta-glucosidase thus represent different forms of glucocerebrosidase. By adding phosphatidylserine and sphingolipid activator protein (SAP-2), monomeric glucocerebrosidase could be completely converted into a form that comigrated with band 2 beta-glucosidase of tissue extracts. The addition of phosphatidylserine only also resulted in a changed mobility of the monomeric enzyme, but the migration in this case differed from that of band 2 beta-glucosidase of tissue extracts. The electrophoretic profile of beta-glucosidase activity of tissue extracts changed upon ethanol/chloroform extraction: the two glucocerebrosidase forms were converted into a band with a mobility identical to that of band 1 beta-glucosidase. Our findings indicate that the interaction of glucocerebrosidase with phospholipid and SAP-2 has major effects on the mobility of the enzyme in the cellulose-acetate gel electrophoresis system. The findings with the cellulose-acetate gel electrophoretic system are discussed in relation to the heterogeneity in glucocerebrosidase observed with sucrose density gradient analysis, immunochemical methods and isoelectric focussing studies.