Root productivity in a lowland tropical rain forest in Mexico

Fine root productivity was estimated in a lowland tropical rain forest at Los Tuxtlas (SE Mexico) and examined in relation to climatic factors. Two root diameter classes were defined (class I,<1 mm; class II, 1–3 mm). Total root productivity was estimated to 1.95 t ha^–1 year^–1, a value which is lower than those reported from other rain forest sites. Significant differences in root dry weight were found among months and between diameter classes throughout the year. Class I monthly means formed two groups: one corresponding to the months of highest precipitation, and the other to the relatively dry season. Class II monthly means also formed two groups, although these were unrelated to the regional precipitation pattern. A multiplicative regression model of productivity on precipitation was significant for both root classes when rainfall data of the previous month were used, while a linear regression model was significant only for class I roots when temperature data of two months before were used; these results suggest a delay in the effect of climatic conditions on root productivity. While the seasonal pattern of root productivity is clearly related to the annual rainfall distribution, the low total annual productivity may be related to the very high soil fertility at Los Tuxtlas.     

High-performance liquid chromatographic method for the determination of mycophenolate mofetil in human plasma

A method for the quantification of mycophenolate mofetil (MMF, CellCept) in plasma using solid-phase extraction and HPLC is described here. A solution of internal standard is added to a 0.5-ml plasma aliquot. The resulting sample is treated with water and dilute HCl and applied to a C₁₈ solid-phase extraction column. After a water wash, the MMF and internal standard are eluted with methanol-0.1 M citrate-phosphate buffer, pH 2.6 (80:20, v/v). A 20-μl aliquot of the eluate is injected onto a C₁₈ column (5 μm particle size, 150 × 4.6 mm I.D.) and eluted at ambient temperature with acetonitrile-0.05 M citrate-phosphate buffer, pH 3.6, containing 0.02 M heptanesulfonic acid (41:59, v/v). Quantification is achieved by UV detection at 254 nm. The method is reproducible, accurate and specific for MMF. Using 0.5 ml of plasma for analysis, the quantification limit is 0.400 μg/ml and the range is 0.400–20 μg/ml. Based on the stability profile of MMF in plasma, it is recommended that blood samples collected following intravenous infusion be immediately stored on ice and that plasma be prepared rapidly, immediately stored frozen at −80°C and analyzed within four months of collection.     

Incomplete cerebral ischemia in the rat provokes increase of tissue and plasma malondialdehyde

Short-term incomplete cerebral ischemia was induced in the rat by bilaterally clamping for 5 min the common carotid arteries; subsequent reperfusion of 10 min was obtained by removing carotid occlusion. At the end of ischemia or reperfusion, animals were sacrificed by decapitation. A control group was represented by sham-operated rats. Peripheral venous blood samples were withdrawn from the femoral vein from rats subjected to cerebral reperfusion 5 min before ischemia, at the end of ischemia, and 10 min after reperfusion. A highly sensitive HPLC method for the direct determination of malondialdehyde, oxypurines, and nucleosides was used on 200 μL of brain tissue and plasma extracts. Incomplete cerebral ischemia induced the, appearance of a significant amout of tissue malondialdehyde (undetectable in control animals) and a decrease of ascorbic acid. A further 6.6-fold increase of malondialdehyde and a 18.5% decrease of ascorbic acid occurred after 10 min of reperfusion. Plasma malondialdehyde, which was present in minimal amount before ischemia, significantly increased after 5 min of ischemia, being strikingly augmented after 10 min of reperfusion. A similar trend was observed for oxypurines and nucleosides. From these data, it can be affirmed that tissue concentrations of malondialdehyde and ascorbic acid, and plasma levels of malondialdehyde, oxypurines, and nucleosides, reflect both the oxygen radical-mediated tissue injury and the depression of energy metabolism thus representing early biochemical markers of short-term incomplete brain ischemia, and reperfusion in the rat.     

A Drosophila hsp70 gene contains long,antiparallel, coupled open reading frames (LAC ORFs) conserved in homologous loci

A clone isolated from a Drosophila auraria heat-shock cDNA library presents two long, antiparallel, coupled (LAC) open reading frames (ORFs). One strand ORF is 1,929 nucleotides long and exhibits great identity (87.5% at the nucleotide level and 94% at the amino acid level) with the hsp70 gene copies of D. melanogaster, while the second strand ORF, in antiparallel in-frame register arrangement, is 1,839 nucleotides long and exhibits 32% identity with a putative, recently identified, NAD⁺-dependent glutamate dehydrogenase (NAD⁺-GDH). The overlap of the two ORFs is 1,824 nucleotides long. Computational analysis shows that this LAC ORF arrangement is conserved in other hsp70 loci in a wide range of organisms, raising questions about possible evolutionary benefits of such a peculiar genomic organization.Correspondence to: Z.G. Scouras     

Latent Transforming Growth Factor-β Binding Protein Domains Involved in Activation and Transglutaminase-dependent Cross-Linking of Latent Transforming Growth Factor-β

Transforming growth factor-β (TGF-β) is secreted by many cell types as part of a large latent complex composed of three subunits: TGF-β, the TGF-β propeptide, and the latent TGF-β binding protein (LTBP). To interact with its cell surface receptors, TGF-β must be released from the latent complex by disrupting noncovalent interactions between mature TGF-β and its propeptide. Previously, we identified LTBP-1 and transglutaminase, a cross-linking enzyme, as reactants involved in the formation of TGF-β. In this study, we demonstrate that LTBP-1 and large latent complex are substrates for transglutaminase. Furthermore, we show that the covalent association between LTBP-1 and the extracellular matrix is transglutaminase dependent, as little LTBP-1 is recovered from matrix digests prepared from cultures treated with transglutaminase inhibitors. Three polyclonal antisera to glutathione S–transferase fusion proteins containing amino, middle, or carboxyl regions of LTBP-1S were used to identify domains of LTBP-1 involved in crosslinking and formation of TGF-β by transglutaminase. Antibodies to the amino and carboxyl regions of LTBP-1S abrogate TGF-β generation by vascular cell cocultures or macrophages. However, only antibodies to the amino-terminal region of LTBP-1 block transglutaminase-dependent cross-linking of large latent complex or LTBP-1. To further identify transglutaminase-reactive domains within the amino-terminal region of LTBP-1S, mutants of LTBP-1S with deletions of either the amino-terminal 293 (ΔN293) or 441 (ΔN441) amino acids were expressed transiently in CHO cells. Analysis of the LTBP-1S content in matrices of transfected CHO cultures revealed that ΔN293 LTBP-1S was matrix associated via a transglutaminasedependent reaction, whereas ΔN441 LTBP-1S was not. This suggests that residues 294–441 are critical to the transglutaminase reactivity of LTBP-1S.     

Refinement by linkage analysis in two large families of the candidate region of the third locus (SCA3) for autosomal dominant cerebellar ataxia type I

The autosomal dominant cerebellar ataxias (ADCA) are clinically and genetically heterogeneous. To date, several loci (SCAI-V) have been identified for ADCA type I. We have studied two large families from the northern part of The Netherlands with ADCA type I with a broad intra-familial variation of symptoms. In both families significant linkage is shown of the disease to the markers of the SCA3 locus on chromosome 14. Through recombinations, the candidate region for SCA3 could be refined to a 13-cM range between D14S256 and D14S81. No recombinations were detected with the markers D14S291 and D14S280, which suggests that the SCA3 gene lies close to these loci. This finding will benefit the individuals at risk in these two families who are seeking predictive testing or prenatal diagnosis.     

Ethylene and growth control in the fringed waterlily (Nymphoides peltata): Stimulation of cell division and interaction with buoyant tension in petioles

The effect of ethylene on petiole growth of the Fringed Waterlily (Nymphoides peltata (S.G. Gmelin) O. Kuntze) changes during leaf ontogeny. During early development (before expansion of laminae), ethylene causes an increase in both cell number and cell size; later in development, promotion of rapid cell expansion is the dominant effect. The early effects may contribute to the accommodation of new leaves to water columns of different depth. The later effects on cell expansion only are shown to contribute to the rapid accommodation of floating leaves when changes in water level submerge the laminae. This kind of accommodation results from an interaction between accumulated ethylene, which increases wall extensibility, and the tension in petioles due to natural buoyancy which, it is suggested, supplements the driving force for cell expansion. Cell age (position) within a petiole and age of the whole petiole influence the growth response to ethylene alone and the amount of extra growth produced by applying tension when ethylene is present. In young petioles, apical cells are highly sensitive to ethylene and tension causes little further growth; older cells in both immature and mature petioles show little response to ethylene unless the petiole is under tension. Young (but not mature) petioles respond slowly to applied tension even in the absence of ethylene. It is concluded that as cells age the driving force for expansion limits increasingly their capacity to respond to the wall-loosening effects of ethylene. Dual sensitivity to ethylene and buoyant tension facilitates rapid accommodation responses but sensitivity of young petioles to tension alone may exclude Nymphoides from habitats where current velocity is appreciable.     

Anion secretion by the isolated rabbit pancreas

The isolated rabbit pancreas secretes a fluid containing chloride and bicarbonate in about equal concentrations. Replacement of bicarbonate by acetate, phosphate or isethionate, replacement of Na⁺ by Li⁺ and addition of ouabain to the bathing medium of the pancreas inhibit the secretion of fluid, chloride and bicarbonate in a similar fashion and by maximally 100%. Replacement of chloride by isethionate inhibits fluid secretion by maximally 50%, chloride secretion by 90% and bicarbonate secretion by 20%. It is concluded that fluid secretion is based on a Na⁺-gradient-dependent bicarbonate influx or proton efflux in the ductular cell, and that the secretion of chloride is secondary to that of bicarbonate.     

Microscopic anatomy of the ovary ofAlouatta caraya

The microscopic structure of theAlouatta caraya ovary is studied in different ages and reproductive stages. The most significant feature seems to be the presence in adult ovaries of abundant glandular interstitial tissue which occupies both the cortex and medulla. It seems to be derived from the theca interna of atretic follicles. Discrete luteinized masses are present in the medulla in all the ovaries observed. Invaginations of the surface epithelium are seen only in infant and juvenile ovaries. The development of cystic follicles seems to be a common pathway of atresia.