tCho Concentration Research Articles

Organic matter composition in sediments of the Oman Margin

The quantity and biochemical composition of organic matter (OM) in the sediments underlying and below oxygen minimum zone (OMZ) in the Arabian Sea were studied to provide information on the diagenetic processes of organic carbon under different environmental conditions. Concentrations of total organic carbon (TOC), total nitrogen (TN) and total hydrolysable amino acids (THAA) were significantly higher in sediments within rather than below OMZ, while those of total carbohydrates (TCHO) were slightly lower in the latter, suggesting the presence of a larger supply of labile compounds into the sea bottom at the shallower site (i.e. within OMZ). Hydrolysable amino acid and carbohydrate contribution to TOC were even lower (about 10% in surficial sediments) than the values obtained from the abyssal oligotrophic North Pacific, suggesting that OM food availability in the Oman Margin sediments within OMZ was lower than that observed at abyssal depths. The presence of the highest THAA and TCHO concentrations in the top 40 mm of the sediment core at both sites reflected the presence of bioturbation processes. In contrast with the general view of the deep sea as a stable and constant system, below OMZ in the Arabian Sea sediments, some differences were observed in the two investigated cores indicating the presence of a certain spatial variability in OM content and diagenesis.

Increased choline levels coincide with enhanced proliferative activity of human neuroepithelial brain tumors.

Proton MR spectroscopy ((1)H MRS)-visible total choline-containing compounds (tCho-compounds) are derivatives of membrane phospholipids and, in part, may act as a long-term second-messenger system for cellular proliferation. Experimental evidence suggests increasing concentrations of tCho-compounds during cellular proliferation. The present study was conducted in order to test the hypothesis that in vivo measurements of tCho-concentrations using (1)H MRS allow assessment of the proliferative activity of neuroepithelial brain tumors presurgically. Single-voxel (1)H MRS (PRESS, TR 1500 ms, TE 135 ms) was performed in 101 patients with neuroepithelial brain tumors prior to surgery and 19 healthy volunteers. Histological diagnoses were confirmed postsurgically according to the WHO classification. Measured tCho-compound signal intensities were corrected for coil loading, numbers of acquisitions and voxel size, and tCho concentrations calculated as institutional arbitrary units. They were matched with the mean immunohistochemical marker of cell proliferation, the Ki-67 (MIB.1) labeling index, using correlation analysis according to Spearman. Compared with low-grade tumors (i.e. WHO grade I/II) and normal white brain matter, high-grade tumors (i.e. WHO grade III/IV) revealed significantly (p < 0.05) elevated labeling indices paralleled by increasingly elevated tCho-concentrations. In contrast tCho-concentrations in low-grade tumor did not differ significantly from physiological values. A highly significant positive correlation (p < 0.0001, r(2) = 0.81) was found between the tCho-concentration and the labeling index. It was concluded that the determination of tCho-concentrations using in vivo (1)H MRS could provide a novel and noninvasive assessment of the proliferative activity of neuroepithelial brain tumors, pointing at (1)H MRS as a useful method for differentiating proliferating from non-proliferating tissues. Hence, potential indications for the clinical application of (1)H MRS are grading tumors presurgically, early detection of anaplastic transformation, and monitoring treatment.

Distribution and Composition of Dissolved and Particulate Organic Carbon in Northern San Francisco Bay During Low Flow Conditions

Dissolved and particulate organic matter were studied in northern San Francisco Bay estuary on seven dates from April to October 1996 when flow from the Sacramento and San Joaquin river Delta was declining. Measurements were made at three to 11 stations (usually eight) along the salinity gradient from the Sacramento River to the Central Bay. Dissolved constituents included monosaccharides (MONO), total carbohydrates (TCHO), dissolved primary amines (DPA), dissolved organic carbon (DOC), and the fluorescence of humic substances (HF). Particulate constituents included bulk suspended particulate matter (SPM), chlorophyll a (CHL), particulate organic carbon (POC) and particulate organic nitrogen (PON). April was distinct from subsequent months due to very high DOC and MONO concentrations and somewhat elevated TCHO, DPA and HF concentrations. DOC, MONO, TCHO and HF concentrations generally decreased with increasing salinity suggesting an upper estuarine source of these constituents. In contrast, DPA had a bimodal distribution suggesting both upper and lower estuarine sources. There was evidence of a persistent, additional source of organic matter near Suisun Bay that was high in DOC and HF, but low in DPA. It was speculated that this material originated from one or more of the following: (a) the San Joaquin River, (b) exchange with the shoals and intertidal reaches of Suisun Bay, and (c) flux of DOC from particulate organic matter (POM). The particulate organic constituents, POC and PON, strongly correlated with SPM but not with CHL, suggesting that sediments were relatively important and phytoplankton were relatively unimportant contributors to POM pools.

Root pruning of apple trees grown at ultra‐high density affects carbohydrate reserves distribution in vegetative and reproductive growth

Five‐year‐old ‘Braeburn’, ‘Royal Gala’, ‘Oregon Red Delicious’, ‘Splendour’, ‘Granny Smith’, and ‘Fuji'/MM. 106 apple (Malus domestica Borkh.) trees growing under an ultra‐high density planting system (20 000 trees/ha) were root pruned in September 1994. Trees were pruned to a depth of 30 cm with a sharp spade along both sides of the row and between trees, 20 and 30 cm from the trunk. Root pruning resulted in decreased tree height, shoot length, branch number, trunk and shoot diameter compared to the control. Root pruning increased floriferousness e.g., the number of flowering spurs in subsequent season. Total carbohydrates (TCHO) and TCHO concentration in tissues of the trees were altered by root pruning treatments. Elevated shoot TCHO concentration was associated with higher flower initiation (flowering spurs per tree in the following season) whereas higher root TCHO was associated with higher total yield. The mean value for root reserves in August 1995 for the control trees was 111 g/plant and 84 g/plant for the 20 cm root‐pruned trees. Fruit yields were 4.1 and 2.6 t/ha respectively. Total yield and average fruit size were reduced by root pruning. The data suggest that root pruning created a lack of balance between reproductive characters and potential yield. This may be explained by reduced shoot leaf area (fewer bourse and shoot leaves) limiting carbohydrate supply and the effects of root pruning on TCHO, yield, and flowering are consistent with the predictions of an earlier model.

Diel flux of dissolved carbohydrate in a salt marsh and a simulated estuarine ecosystem

The concentrations of total dissolved carbohydrate (TCHO), monosaccharide (MCHO) and polysaccharide (PCHO) were followed over a total of ten diel cycles in a salt marsh and a 13 m3 seawater tank simulating an estuarine ecosystem. Their patterns are compared to those for total dissolved organic carbon (DOC), ΣCO2, pH, O2, chlorophyll a, phaeopigments and solar radiation. During 5 of the 6 marsh studies, PCHO underwent periods of sustained accumulation starting in the late morning or early afternoon and continuing into the early evening. These periods possibly represent release of recently synthesized PCHO from phototrophs. similar patterns were not found in the tank although direct associations between TCHO and phaeopigment dynamics suggest that zooplankton excretion was an important source of dissolved carbohydrate. The numbers of planktonic bacteria determined in one tank study increased rapidly during a late morning PCHO pulse and varied inversely with PCHO throughout the afternoon and evening, indicating that they were able to respond rapidly and control natural substrate concentrations on a time scale of a few hours. MCHO fluctuated to a much lesser extent than PCHO at both locations with levels possibly maintained near the bacterial uptake threshold or in a closely regulated steady state. TCHO concentration changes over 2-to 3-h sampling intervals suggest very rapid net system release and uptake with summer rates frequently exceeding 30 μg C l-1h-1 in the marsh and 20 μg C l-1 h-1 in the tank.