Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

Modulation of whole body protein metabolism, during and after exercise, by variation of dietary protein

The aim of this study was to investigate dietaryprotein-induced changes in whole body leucine turnover and oxidationand in skeletal muscle branched chain 2-oxo acid dehydrogenase (BCOADH) activity, at rest and during exercise. Postabsorptive subjects receiveda primed constant infusion ofL-[1-¹³C,¹⁵N]leucinefor 6 h, after previous consumption of a high- (HP; 1.8 g · kg¹ · day¹,n = 8) or a low-protein diet (LP; 0.7 g · kg¹ · day¹,n = 8) for 7 days. The subjects werestudied at rest for 2 h, during 2-h exercise at 60% maximum oxygenconsumption, then again for 2 h at rest. Exercise induced a doubling ofboth leucine oxidation from 20 µmol · kg¹ · h¹and BCOADH percent activation from 7% in all subjects. Leucine oxidation was greater before (+46%) and during (+40%,P < 0.05) the first hour of exercisein subjects consuming the HP rather than the LP diet, but there was noadditional change in muscle BCOADH activity. The results suggest thatleucine oxidation was increased by previous ingestion of an HP diet,attributable to an increase in leucine availability rather than to astimulation of the skeletal muscle BCOADH activity.

     

A re-evaluation of the surface complexity of the intact erythrocyte

Surface proteins and glycoproteins of intact human red blood cells were labelled with ¹²⁵I by the lactoperoxidase method. The radioactive proteins were then separated in each of the Fairbanks and Laemmli one-dimensional polyacrylamide gel electrophoresis systems. The radioactive polypeptides had different mobilities in the two systems, largely due to the anomalous migration of glycoproteins in polyacrylamide gels. A two-dimensional system was therefore developed using the Fairbanks and Laemmli buffer systems to exploit these anomalies. This procedure clearly resolved radioactive glycoproteins and proteins and enabled the identification of many more surface components than had previously proved possible.     

Studies on the regulation of the concentration of androgens and androgen receptors in nuclei of prostatic cells.

Experiments were performed to assess the effect of intracellular androgen metabolism and the availability of cytoplasmic receptors on the concentration of androgens and androgen receptors in nuclei of prostatic cells. It was found that androgens are incorporated into the nucleus by a regulated, selective process which appears to limit the type and amount of androgen transported across the nuclear membrane. The metabolic conversion of testosterone to dihydrotestosterone which takes place in cytoplasm does not reduce transport and, very likely, affects only the ratio of testosterone and dihydrotestosterone transferred into the nucleus. In vivo, when the intranuclear concentration of androgens approaches 250 nM (8 pmol per mg DNA), an apparent concentration ceiling is reached even in the presence of a downward concentration gradient that would be expected to promote further transport across the nuclear membrane. This finding strongly suggests that in vivo the nuclear membrane acts as a barrier to the passage of androgens and, therefore, mitigates against the possibility that passive diffusion is an important mechanism of afferent transport of androgens into the nucleus. The ability of the nucleus to concentrate testosterone and dihydrotestosterone was clearly demonstrated in vivo when cytoplasmic concentrations of androgens of approximately 20 nM were accompanied by intranuclear concentrations in the vicinity of 250 nM. Since the measured concentration of testosterone and dihydrotestosterone in prostate of several species fall within the 5-20 nM range, it is evident that androgen concentrations in the nucleus as high as 250 nM may be typical of the physiological steady state. At the latter concentration the nucleus contains 60 000 androgen molecules: in approximate terms one third of this total is bound to a large molecular weight component of the nucleus, one third is bound to a 3.3 S receptor and one third is free or loosely bound. Since 60 000 androgen molecules and 20 000 receptor molecules appear in the nucleus before transport stops, it seems that the quantity of 4.4 S cytoplasmic receptor estimated at 174 plus or minus 24 pmol per mg protein (equivalent to about 8000 molecules per cell) is insufficient to account for the total influx of androgens and androgen receptors into the nucleus. Thus, although these results support the view that cytoplasmic receptors and the capacity to transport androgens are closely linked phenotypic markers of intracellular steroid hormone action, they suggest that the control of androgen concentration in the nucleus is achieved in a more intricate fashion than simply through a dependence on the presumed translocation of 4.4 S androgen-receptor complex into the nucleus.     

The isolation of coated vesicles from protoplasts of soybean

Fractions enriched in coated vesicles were obtained from protoplasts derived from suspension cultured Glycine max (L.) Merr. cells. Initial enrichment was achieved by isopycnic centrifugation of a protoplast homogenate through a linear sucrose gradient in a vertical rotor. The coated-vesicle fractions from this gradient were pooled and centrifuged through a second linear sucrose gradient in a rate zonal fashion to remove the larger contaminating membrane vesicles. The most prominent polypeptide in the coated-vesicle fractions, plant clathrin, had a relative molecular mass of approx. 190 kdalton as determined by sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. Other enriched polypeptides included bands at 105, 100, 96, 64, 50, 38 and 32 kdalton. This method was compared with a procedure utilizing sucrose step gradients for preparing coated vesicles from soybean protoplasts. The effectiveness of the isopycnic-rate zonal centrifugation procedure was also tested for the preparation of bovine-brain coated vesicles.NRCC No. 23142     

Evidence for an Na+-K+-Cl- cotransporter in mammalian type I vestibular hair cells

In amniotes,there are two types of hair cells, designated I and II, that differ intheir morphology, innervation pattern, and ionic membrane properties.Type I cells are unique among hair cells in that their basolateralsurfaces are almost completely enclosed by an afferent calyceal nerveterminal. Recently, several lines of evidence have ascribed a motilefunction to type I hair cells. To investigate this, elevated externalK⁺, which had been used previouslyto induce hair cell shortening, was used to induce shape changes indissociated mammalian type I vestibular hair cells. Morphologicallyidentified type I cells shortened and widened when the externalK⁺ concentration was raisedisotonically from 2 to 125 mM. The shortening did not require externalCa²⁺ but was abolished whenexternal Cl was replacedwith gluconate or sulfate and when externalNa⁺ was replaced withN-methyl-D-glucamine.Bumetanide (10-100 µM), a specific blocker of theNa⁺-K⁺-Cl cotransporter,significantly reduced K⁺-inducedshortening. Hyposmotic solution resulted in type I cell shape changessimilar to those seen with highK⁺, i.e., shortening and widening.Type I cells became more spherical in hyposmotic solution, presumablyas a result of a volume increase due to water influx. In hypertonicsolution, cells became narrower and increased in length. These resultssuggest that shape changes in type I hair cells induced by highK⁺ are due, at least in part, toion and solute entry via anNa⁺-K⁺-Cl cotransporter, whichresults in cell swelling. A scheme is proposed whereby the type I haircell depolarizes and K⁺ leaves thecell via voltage-dependent K⁺channels and accumulates in the synaptic space between the type I haircell and calyx. Excess K⁺ couldthen be removed from the intercellular space by uptake via thecotransporter.