Concentration and transport of dissolved and suspended substances in the Orinoco River

The Orinoco River, which is hydrologically unregulated and has a minimally disturbed watershed, was sampled quantitatively over a four-year interval. In conjunction with the sampling, a method was developed for quantifying statistical uncertainty in the estimates of annual transport. The discharge-weighted mean concentration of total suspended solids in the Orinoco River is 80 mg/l, which corresponds to total annual transport of 90 × 10⁶ t/y, or, expressed per unit of watershed area, 960 kg/ha/y, of which 96% is inorganic. The mean for dissolved solids is 34 mg/l, of which 25 mg/l is inorganic. The total transport of inorganic material, with a small allowance for bedload, is 128 × 10⁶ t/y, which corresponds to an erosion rate of 4 cm/1000 y. Concentrations of dissolved and suspended constituents derived from rock weathering are very low because of dilution from high runoff (1190 mm/y), coverage of the southern part of the drainage by shield rock, and minimal watershed disturbance. Seasonal patterns in dissolved and suspended constituents are repeated with a high degree of consistency from one year to the next. For most variables, relationships between transport and discharge are described adequately by a power function. There are three categories of response to changing discharge: purging (exponent > 1: soluble organic fractions and all particulate fractions), dilution (exponent 0–1: major ionic solids and silicon), and conservation (exponent < 0: nitrate, interannual). Variability across seasons and across years is highest for the particulate constituents, but within this group variability is lower for the organic than for the inorganic components. Major ions that originate primarily from the atmosphere have a higher seasonal variability than major ions that originate primarily from weathering. Potassium and soluble silicon have the lowest variabilities. Variability is much lower across years than across seasons for most constituents. Because of high runoff per unit area, the Orinoco drainage has a high specific transport of organic carbon (72 kg/ha/y, 6.8 × 10⁶ t/y, 1.6% of global river transport), even though the concentrations of organic carbon in the river are not exceptionally high (mean, 4.4 mg/l dissolved, 1.4 mg/l particulate). Concentrations of ammonium (35 μg/l as N) and of nitrate (80 μg/l as N) are high given the undisturbed nature of the watershed and the high amount of runoff. The high transport rate for total nitrogen (5.7 kg/ha/y, 0.54 × 10⁶ t/y, l.5% of global river transport) can be sustained only by high rates of nitrogen fixation within the watershed. Concentrations of soluble phosphorus are within the range expected for undisturbed river systems (20 μg/l), but concentrations of particulate phosphorus are low because the amounts of particulate matter are small and the phosphorus per unit weight of suspended matter is low. Phosphorus transport (0.75 kg/ha/y) can be accounted for easily by weathering of the parent material, even within the Guayana Shield, where weathering rates are lowest. Biological modification of nutrient and carbon fractions during transit along the main stem are minimal.     

Spatial population structure of the Neotropical tiger catfish Pseudoplatystoma metaense: skull and otolith shape variation

Using geometric morphometrics, the skull and otolith of tiger catfish Pseudoplatystoma metaense were analysed to identify population structure in tributaries of the Apure River (i.e. the Sarare, Caparo, Guanare, Portuguesa and San Carlos Rivers) in the Orinoco basin, Venezuela. The analyses show uniformity in skull and otolith shapes of P. metaense within and among four tributaries, with only the Caparo River showing significant differences. Within the Apure basin, the stock of P. metaense was differentiated through spawning, refuge and nursery areas. This study concludes that populations of P. metaense from each major tributary in the Orinoco basin should be considered as part of a metapopulation system for management purposes. Human disturbances in the catchment have directly reduced the spawning areas available to this species, decreased the total biomass and changed the spatial distribution of spawning areas.     

Ecology of the phytoplankton of the River Moselle: effects of disturbances on community structure and diversity

A data set on community composition of the phytoplankton of the River Moselle (France) has been used for testing the intermediate disturbance hypothesis (IDH). After a short presentation of the ecology of the river and of its phytoplankton, the main changes in composition and diversity of the suspended algal assemblage are described. It is emphasized that discharge fluctuations, related to weather changes, play a key role, but that biotic factors such as grazing and parasitism may also influence diversity in stable summer conditions.     

Transport of phosphorus,nitrogen, and carbon by the Apure River,Venezuela

The concentrations and transport of carbon, nitrogen, and phosphorus were studied in the Apure River, Venezuela, over a period of 21 months. The drainage basin, which is in western Venezuela, encompasses 167,000 kM², most of which has low relief and supports tropical savanna vegetation. Average runoff for the period of study was 361 mm/year. Discharge-weighted mean concentrations were 188 ug/l for total P, 957 ug/l for total N, and 9.8 mg/l for organic C. Annual transport was 0.68 kg· ha^-1· year^-1 for total P, 3.45 kg · ha^-1· year^-1 for total N, and 35.4 kg · ha^-1 · year^-1 for organic C. Particulate matter accounted for 68% of P, 54% of N, and 37% of C transport. The yield of carbon from the Apure watershed agrees well with empirical predictions, based mostly on the temperate zone, for watersheds of similar size and water yield.Seasonal patterns in chemistry are tied strongly to the hydrologic cycle. When the wet season begins, rising water flushes organic matter from side channels and produces a sharp increase in particulate C and N. Particulate P, which is associated more with mineral material, also increases during rising water. All dissolved constituents except inorganic C also increase over the rising-water phase. As the river inundates the floodplain, the concentration of nitrate declines, whereas the concentrations of dissolved organic C and N continue to rise. At high water the floodplain appears to store sediments that are later remobilized. During low water, all fractions except dissolved inorganic C tend to be at minimum concentration.Soluble reactive P, total dissolved P, dissolved inorganic C, and dissolved organic C were successfully modelled as hyperbolic functions of discharge. No significant relationships were found between concentration and discharge for any particulate fraction because the flushing and storage mechanisms affecting these fractions occurred within specific hydrologic phases, rather than as a smooth function of discharge. No significant relationships were found for any nitrogen fraction. For nitrate, and thus for total dissolved N, of which nitrate is a major component, poor conformance to standard models is explained by association of key mechanisms (e.g. uptake) with specific hydrologic phases. Particulate components and nitrate in this sense violate the continuity assumptions implicit in the standard models.     

Regioselective deacetylation of peracetylated monosaccharide derivatives by polyethylene glycol-modified lipase for the oligosaccharide synthesis

Lipase modified with polyethylene glycol became soluble and active in organic solvents, and catalyzed regioselective deacetylation of peracetylated monosaccharide derivatives in 1,1,1-trichloroethane. The deacetylation occurred only at the positions of C-4 and C-6 of the glycopyranoside ring. Especially, peracetylated methyl -D-xylopyranoside and peracetylated L-serine--D-xylopyranoside were hydrolyzed only at the position of C-4. Subsequently, one of the resulting products, that is L-serine-2,3-di-O-acetyl--D-xylopyranoside, was coupled with galactose residue to obtain L-serine-4-O-(-D-galactopyranosyl)--D-xylopyranoside, a model compound of the carbohydrate-protein linkage region of proteoglycans.     

Enzymatic synthesis of poly-β-hydroxybutyrate inZoogloea ramigera

The enzyme activity synthesizing poly--hydroxybutyrate (PHB) was mainly localized in the PHB-containing particulate fraction ofZoogloea ramigera I-16-M, when it grew flocculatedly in a medium supplemented with glucose. On the other hand, the enzyme activity remained in the soluble fraction, when the bacterium grew dispersedly in a glucose-starved medium.The soluble PHB synthase activity became associated with the particulate fraction as PHB synthesis was initiated on the addition of glucose to the dispersed culture. Conversely, the enzyme activity was released from the PHB-containing granules to the soluble fraction when the flocculated culture was kept incubated without supplementing the medium with glucose.PHB synthase was also incorporated into the newly formed PHB fraction when partially purified soluble PHB synthase was incubated withd(-)--hydroxybutyryl CoA in vitro.Although attempts to solubilize the particulate enzyme were unsuccessful, and the soluble enzyme became extremely unstable in advanced stages of purification, both PHB synthases had the same strict substrate specificity ford(-)--hydroxybutyryl CoA, and showed the same pH optimum at 7.0.Non-Standard Abbreviations PHB poly--hydroxybutyrate     

Interactions of Aβ(1–40) with Glycerophosphocholine and Intact Erythrocyte Membranes: Fluorescence and Circular Dichroism Studies

Deposition of amyloid peptide in human brain in the form of senile plaques is a neuropathological hallmark of Alzheimers disease (AD). Levels of a phospholipid breakdown product, glycerophosphocholine (GPC), also increase in AD brain. The effect of GPC on amyloid (1–40) peptide (A) aggregation in PBS buffer was investigated by circular dichroism and fluoresence spectroscopy; interactions of A and GPC with the intact erythrocyte membrane was examined by fluoresence spectroscopy. Fluorescamine labeled A studies indicate GPC enhances A aggregation. CD spectroscopy reveals that A in the presence of GPC adopts 14% more -sheet structure than does A alone. Fluorescamine anisotropy measurements show that GPC and A interact in the phospholipid head-group region of the erythrocyte membrane. In summary, both soluble A and GPC insert into the phospholipid head-group region of the membrane where they interact leading to -sheet formation in soluble A which enhances A aggregation.     

Membrane pathways for water and solutes in the toad bladder: II. Reflection coefficients of the water and solute channels

Summary Urea and water transport across the toad bladder can be separately activated by low concentrations of vasopressin or 8 Br-cAMP. Employing this method of selective activation, we have determined the reflection coefficient () of urea and other small molecules under circumstances in which the bladder was transporting urea or water. An osmotic method for the determination of was used, in which the ability of a given solute to retard water efflux from the bladder was compared to that of raffinose (=1.0) or water (=0). When urea transport was activated (low concentration of vasopressin), for urea and other solutes was low, (_urea,0.08–0.39;_acetamide, 0.55; _{ethylene glycol}, 0.60). When water transport was activated (0.1mm 8 Br-cAMP) _urea approached 1.0 _urea also approached 1.0 at high vasopressin concentrations. In a separate series of studies, _urea was determined in the presence of 2×10^–5 m KMnO₄ in the luminal bathing medium. Under these conditions, when urea transport is selectively blocked, _urea rose from a value of 0.12 to 0.89. Thus, permanganate appears to close the urea transport channel. These findings indicate that the luminal membrane channels for water and solutes differ significantly in their dimensions. The solute channels, limited in number, have relatively large radii. They carry a small fraction (approximately 10%) of total water flow. The water transport channels, on the other hand, have small radii, approximately the size of a water molecule, and exclude solutes as small as urea.     

Seasonal alternation of lentic/lotic conditions in the Mapire system,a tropical floodplain lake in Venezuela

We studied the changing hydrological conditions of a transient system at the Mapire River mouth (Orinoco) and their effect on hydrochemistry of the system at six locations. Subjected to strong annual waterlevel fluctuations, the Orinoco River acts as a dam to the Mapire River discharge, resulting in the formation of a standing lake-like waterbody that covers the gallery forest to the canopy for five to six months. The Mapire floodplain fills primarily with Mapire waters and only secondarily with Orinoco water. The latter enters into the Mapire basin, but mixing of both waters is poor, resulting in chemically and physically different waterlayers. A significant thermal stratification is observed. This transient lake revverts to flowing conditions during the dry season. The Mapire River moutth, therefore, behaves as a cyclic system in which lotic/lentic and terrestrial/ aquatic conditions alternate seasonally. Some ecological implications are suggested and comparisons with similar systems are made.     

Spawning time and early life history of Murray cod, <Emphasis Type="Italic">Maccullochella peelii</Emphasis> (Mitchell) in an Australian river

Synopsis I investigated aspects of the early life history of Murray cod in the Broken River, southern Murray-Darling Basin, Australia. I documented patterns in abundance, length, age and the amount of yolk of drifting free embryos and estimated spawning periods for adult Murray cod in two reaches throughout each breeding season between mid-October and mid-December from 1997 to 2001. Free embryos began drifting in late-October and continued until mid- to late-December. Abundances of drifting free embryos showed no obvious peak in most years and were unrelated to discharge. Length, amount of yolk and age typically varied with sampling date, but only age showed strong and negative correlations with temperature. Thus, it appears that temperature affected rates of development, and that developmental stage, not length or age, was likely to be the determinant for when free embryos left the paternal nest. Most free embryos were estimated to have spent between 5 and 7 days drifting. Spawning of Murray cod in the Broken River usually commenced in mid-October and continued until at least early December. Initiation of spawning was associated with temperatures of 15°C and above, but discharge was highly variable, and no other environmental variables were consistent across years. The mid-point of spawning – usually in the first week of November – is considered a more significant time, because it likely coincides with peak spawning, and conditions during and immediately after this time are expected to be optimal for the survival of eggs and free embryos.     

Particle pathways of Niagara river water in Lake Ontario affecting bottom sediment contamination

The results of integrated multidisciplinary studies of the transport and pathways of toxic contaminants entering Lake Ontario through the Niagara River are summarized. The factors controlling the transport and distribution of contaminants are: (i) Niagara River mixing characteristics; (ii) prevailing local wind conditions and large scale lake-wide circulation features, and (iii) suspended sediment load and the partitioning of the contaminants onto the suspended solids. Physical limnological studies included a variety of direct measurements to delineate the nearfield and farfield mixing characteristics of the river plume in terms of the prevailing winds and large scale lake circulation. In the nearfield region of the plume, around the river mouth, contaminant transport was affected by the initial momentum and buoyancy of the river water mass and a sharp thermal front that is generally present through the stratified season. After the initial momentum is dissipated, the weakly buoyant river plume responds to the prevailing winds and lake-wide circulation. Adsorbed contaminants rapidly settle once the initial momentum of the river plume is dissipated but the dissolved contaminants are transported into the farfield regions in the lake and after becoming entrained in the strong south shore eastward flowing boundary current are carried toward the St. Lawrence River outflow. Only about ten percent of this eastward flowing transport exits via the St. Lawrence River, the remainder is recirculated back into the main lake. A contaminant transport model of the Niagara River Plume incorporating a hydrodynamic model, observed plume mixing characteristics and chemical partitioning was used to simulate the compartmental distribution (adsorbed vs dissolved) of selected toxic chemicals distribution observed in the nearfield region of the plume.     

Random chemical modification of the oxygen-linked chloride-binding sites of hemoglobin: Those in the central dyad axis may influence the transition between deoxy- and oxy-hemoglobin

The features of random chemical modification are defined with reference to acetylation of bovine hemoglobin, which has been performed in a random manner so that all of the amino groups that participate in functional chloride binding (i.e., those that are oxygen-linked) could be identified. Random chemical modification, which has objectives different from those of both specific (selective) and extensive chemical modification, has been achieved for bovine hemoglobin with the mild reagent,¹⁴C-methyl acetate phosphate; retention of function was demonstrated by a Hill coefficient ofn=2.2 for the modified hemoglobin. After removal of unmodified Hb chains, the mixture of randomly modified acetylated or chains was subjected to tandem treatment with trypsin and chymotrypsin. Peptides were purified by HPLC and identified by amino acid analysis. The amount of radioactivity in the acetylated amino group of a purified peptide was taken as an estimate of the degree of chloride binding. For bovine Hb, two amino groups of the -chain (Val-1 and Lys-99) and three amino groups of the -chain (Met-1, Lys-81, and Lys-103) were shown to be oxygen-linked (i.e., to have incorporated significantly more radioactivity in the deoxy conformation compared to the same site in the oxy conformation). Three of these sites were already known chloride-binding sites [i.e., Val-1(), the N-terminus of the -chain, and two sites between the 2 -chains of bovine hemoglobin, Met-1() and Lys-81(); these findings support the conclusions of the random modification approach. Two other chloride-binding sites, Lys-99() and Lys-103(), align the sides of the central dyad axis connecting the two well-known major chloride-binding sites of bovine Hb. The interrelationship of these five chloride-binding sites was assessed by improved molecular graphics. When viewed through the central dyad axis, the functional chloride-binding sites in the central cavity appear to be symmetrically related and to connect the two major chloride-binding sites. Modifiers or mutants that are directed at these regions in the central dyad axis may favor the deoxy conformation to provide a lower oxygen affinity by preventing the constriction of the central cavity that normally occurs upon oxygenation.     

Interaction of synthetic Alzheimerβ-protein-derived analogs with aqueous aluminum: A low-field27Al NMR investigation

Synthetic peptides corresponding to the soluble Alzheimer-protein, i.e., 1–40 and 6-25, were utilized to investigate the association of aluminum using low-field²⁷Al nuclear magnetic resonance (NMR) spectroscopy and reversed-phase high-performance liquid chromatography (RP-HPLC). Addition of 1-40 or 6-25 to aqueous Al³⁺ gives rise to a²⁷Al NMR signal corresponding to the association of Al³⁺ with the peptides; this effect is not easily reversed by EDTA. Based on the relative intensity of the Al³⁺-peptide signal between pH 4 and 6, there are at least 4 Al³⁺ ions associated with each peptide molecule. Microheterogeneity is observed with RP-HPLC on incubating solutions of Al³⁺ with 1-40 and 6-25. The²⁷Al NMR spectra of chromatographically pure fractions of 1-40 and 6-25 indicate that the peptide-associated Al³⁺ is released below pH 3.5. We propose that soluble 1-40 provides an anchor for Al³⁺ to bind, eventually leading to an increased deposition of amyloid in the Alzheimer brain.     

Taurine and β-alanine uptake in primary astrocytes differentiating in culture: Effects of ions

The effects of ions on taurine and -alanine uptake were studied in astrocytes during cellular differentiation in primary cultures. The uptakes were strictly Na⁺-dependent and also inhibited by the omission of K⁺ and in the presence of ouabain suggesting that their transport is fuelled mainly by these cation gradients. Two sodium ions were associated in the transport of one taurine and -alanine molecule across cell membranes. A reduction in Cl^– concentration also markedly inhibited the uptake of both amino acids, indicating that this anion is of importance in the transport processes. The similar ion dependency profiles of taurine and -alanine uptake corroborate the assumption that the uptake of these amino acids in astrocytes is mediated by the same carrier. In Na⁺- and K⁺-free media both taurine and -alanine uptakes were reduced significantly more in 14-day-old or older than in 7-day-old cultures. No significant changes occurred in the coupling ratio between Na⁺ and taurine or -alanine as a function of spontaneous cellular differentiation or upon dBcAMP treatment. These results suggest that the uptake systems of these structurally related amino acids in astrocytes have reached a relatively high degree of functional maturity by two weeks in culture.     

Particulate organic carbon, sterols, fatty acids and pigments in the Amazon River system

Water samples were collected from the Amazon River system during a high flood period, in June 1989, and lipids associated with particles retained on GF/F filters were examined. Particles showed a highly variable organic carbon content (1.8–29.0%). Corresponding organic carbon concentrations varied from 0.36 to 1.13 mg/l. The flood conditions encountered during the sampling period may feed exceptional inputs of soil organic matter into the tributaries and the Amazon River. Composition and concentration of sterols, fatty acids and pigments were determined to estimate the relative portion of terrigenous and autochthonous fraction of this complex organic matter. Sterol distribution patterns were similar to other equatorial rivers, in the Orinoco (Venezuela) and Solo (Indonesia). In comparison with the dominant profile of the Amazon system, distinct patterns were found in the Trombetas River (29^5,22 27⁵ 29⁵ 28⁵, 28^5,22) and in the Tapajos River (27^5,22 > 27⁵ 29⁵, 28⁵, 28^5,22). These fingerprints reflect different vegetation types of drainage basins and distinct planktonic pools. The distribution of even-carbon numbered saturated fatty acids in the carbon range of 24–36 revealed low inputs of constituents associated with cuticular waxes of vascular plants in Black waters and in the Tapajos River (200 ng/l), higher in White waters (328–483 ng/l) and highest in the Trombetas River (704 ng/l) and in stagnant waters of a small lake close to the Amazon (1088 ng/l). Pigment concentrations showed that in the main river and most tributaries vegetal carbon did not represent more than 2%, except for the Tapajos River (6.2%) and in relatively stagnant waters sampled along the main river (9.2%). Based on relative abundance of Chl b, Chl c, fucoxanthin, peridinin, alloxanthin, and zeaxanthin, various phytoplanktonic assemblages were evidenced in the Amazon River system. Branched fatty acids in the carbon range of 15–17 gave insight into bacterial signatures. They showed low microbial contribution to the fatty acid pool, with slightest higher contribution in a swamp of stagnant waters and in the White waters of the Solimoes River.     

Cytokinin metabolism in Phaseolus vulgaris L.

The major cytokinins in stems of decapitated, disbudded bean plants have been identified by enzymic degradation, Sephadex LH20 and reversed phase high performance liquid chromatography, and by combined gas chromatography-mass spectrometry as 6-(4-hydroxy-3-methylbut-trans-2-enylamino)-9--D-ribofuranosylpurine (zeatin riboside), 6-(4-hydroxy-3-methylbutylamino)-9--D-ribofuranosylpurine (dihydrozeatin riboside), and the 5-phosphates of these compounds (zeatin ribotide and dihydrozeatin ribotide). Minor cytokinins in this tissue were tentatively identified as dihydrozeatin-O--D-glucoside and zeatin ribotide-O--D-glucoside. [8-¹⁴C-]Dihydrozeatin appeared to be rapidly metabolized to dihydrozeatin ribotide when supplied to segments of stems from decapitated plants. These results are discussed in relation to the metabolism and distribution of cytokinins in the whole plant.Abbreviations TEAB triethyl ammonium bicarbonate - UV ultra-violet - GCMS gas chromatography-mass spectrometry - HPLC high performance liquid chromatography - TMS trimethyl silyl     

DiO-C3-(5) and DiS-C3-(5): Interactions with RBC,ghosts and phospholipid vesicles

Summary The transport of solutes by bacteria has been studied for about thirty years. Early experiments on amino acid entry and galactoside accumulation provided concrete evidence that bacteria possessed specific transport systems and that these were subject to regulation. Since then a large number of transport systems have been discovered and studied extensively. Many of these use entirely different strategies for capturing or accumulating substrates. This diversity reflects variation in the availability of nutrients and ions in the different environments tolerated and inhabited by microorganisms. Examination of a few bacterial transport systems provides an opportunity to gain insight into a wide range of topics in the area of membrane transport. These include: the identification of carrier proteins and their arrangement in the membrane, the regulation of transport protein synthesis by environmental factors, and the localization of transport proteins to their extracytoplasmic destinations.It has been possible to construct a number of bacterial strains in which the gene (lacZ) which codes for the cytoplasmic enzyme -galactosidase is fused to genes which code for transport proteins. The following article is intended to illustrate how these gene fusions have been used to study the regulation and structure of transport proteins inEscherichia coli.     

Zooplankton abundance and transport in a tropical white-water river

Zooplankton abundance and transport were studied in the Apure River of western Venuzuela over a 15-month period. Much of the lower portion of the drainage basin, which is an extensive savanna of low relief, is subject to seasonal flooding. Although more than 50 zooplankton species were recorded during the study, nine rotifer species accounted for more than 90% of total density (mean, 138 individuals · L^-1). Copepods were represented primarily by Mesocyclops decipiens. Most cladocerans were planktonic, but cladocerans were not abundant. Crustaceans comprised 46% of annual mean zooplankton biomass (1.9 gC·L^-1) but only 2% of zooplankton numbers. The annual transport of zooplankton biomass from the watershed was 29 300 kgC. Zooplankton abundance showed a strong, inverse relationship to discharge. Secondary branches (caños) of the braided channel appeared to be the primary source areas, but populations of some species also reproduced in the main channel at low water. As the river began to rise, caños were flushed and thus abruptly ceased to serve as source areas. Zooplankton transport fell sharply and remained low until the river inundated the floodplain. Secondary production in the floodplain was exported to the river as long as a connection existed. After drainage ceased from the floodplain, transport fell to very low levels until caños again became suitable habitat. Seasonal fluctuations in river level regulate the development of source areas suitable for zooplankton growth and control the export of plankton from the source areas. Plankton in the running waters reproduce only at low water.     

Iron and copper in Plagioscion squamosissimus (Piscis: Sciaenidae) from the Orinoco river, Venezuela

Bauxite explotation of the Orinoco River in recent years is an important source of heavy metals discharge in the ecosystem, changing the natural biochemical flow of these elements and their concentrations in water, sediment and organisms. Iron and copper concentrations were measured in the fish Plagioscion squamosissimus in the Orinoco river, by sampling the fish population for three months (September-November 1998) in the main channel of the middle Orinoco (07 degrees 38' 21.2" N; 66 degrees 19' 10.9" W) and in Castillero lagoon (7 degrees 39' 09" N; 66 degrees 09' 00" W) with 2 and 4 cm mesh sizes. The internal organs of 30 fishes per month and site were stove-dried at 80 degrees C, pulverized and dried in disecator for 30 min to use as indicators with the acid digestion method for predicting the effect of heavy metals. We found relatively high values of iron and copper concentrations in fishes of the lagoon, and high seasonal variations in the iron concentration.     

Cell wall localization of dihydroflavonol-glucoside β-glucosidase in flowers of Petunia hybrida

Limbs of flower buds from Petunia hybrida were investigated for -glucosidase activity with dihydroflavonol-glucosides and 4-methyl-umbelliferyl--D-glucoside as substrates. Dihydroflavonol-glucoside -glucosidase is localized in the cell wall. This activity has an acid pH optimum and is also active toward 4-methyl-umbelliferyl--glucoside. Besides this activity a neutral -glucosidase is present. This activity is soluble and is not active toward dihydroflavonol-glucosides. Using starch gel electrophoresis it was shown that no difference in -glucosidase activity is present between mutants able to convert dihydroflavonols into anthocyanins and mutants accumulating dihydroflavonol-glucosides. It is concluded that -glucosidase activity is not involved in anthocyanin synthesis.Abbreviations 4MU--glc 4-methylumbelliferyl--D-glucopyranoside - dHQ-7-g dihydroquercetin-7-glucoside - dHQ-4-g dihydroquercetin-4-glucoside - dHM-4-g dihydromyricetin-4-glucoside Deceased