Effects of Germanium (Ge) on the silica spicules of the marine sponge Suberites domuncula: Transformation of spicule type

Germanium (Ge), in the form of germanic acid, at a Ge/Si molar ratio of 1.0 inhibits gemmule development and silica deposition in the marine demosponge Suberites domuncula. Lower Ge/Si ratios inhibit the growth in length of the silica spicules (tylostyles) producing short structures, but with relatively normal morphology and close to normal width; spherical protuberances occasionally occur on these spicules. A few of the short spicules possess completely round rather than pointed tips. Many of the latter develop when Ge is added (pulsed) to growing animals, thus inducing a change in spicule type. These results indicate that the growth in length of the axial filament is more sensitive to Ge inhibition than is silica deposition and that pointed spicule tips normally develop because the growth of the axial filament at the spicule tip is more rapid than silica deposition. Newly formed spicules initiate silica deposition at the spicule head but the absence of Ge-induced bulbs as in freshwater spicules (oxeas) leaves open the question of whether there is a silicification center(s) present in Suberites tylostyles. The morphogenesis of freshwater oxeas and of marine tyolstyles appears fundamentally different-bidirectional growth in the former and unidirectional growth in the latter. X-ray analysis demonstrate relatively uniform Ge incorporation into the silica spicules with considerable variation from spicule to spicule in the incorporated level. Increased silicic acid concentration induces the formation of siliceous spheres, suggesting that the axial filament becomes prematurely encased in silica.     

Effects of germanium on the morphology of silica deposition in a freshwater sponge

The effect of germanium on the secretion of siliceous spicules by the freshwater sponge Spongilla lacustris was investigated by exposing germinating and hatching gemmules to varying concentrations of germanium (Ge) in the presence of silicon (Si). Results were analyzed quantitatively and qualitatively and demonstrate that a [Ge]/[Si] (= molar ratio) of 1.0 completely inhibits silicon deposition. Intermediate ratios (0.5, 0.1, 0.01) which are permissive to spicule appearance result in fewer, shorter, and thinner spicules, in proportionately fewer microscleres, and in short bulbous megascleres. The size of the bulb increases with increasing [Ge]/[Si], while the length of the bulbous megascleres decreases with increasing [Ge]/[Si]. Microscleres do not demonstrate these graded responses suggesting that they are secreted in an all or none manner. Swellings produced in pond water and bulbs produced in germanium appear to decrease in size with time indicating a spreading of the accumulated silica. The effect of germanium on spicule secretion can be partially explained by its ability to uncouple the growth in length of the axial filament from the growth of the surrounding silicalemma. Under these conditions excess silicalemma is produced in which silica accumulates as bulbs in short spicules. Continuous exposure to Ge is necessary to produce this altered morphology. It is conjectured that the bulbs may be retained due to an inhibition of spreading. which in turn may be caused by the incorporation of germanium into the silica.     

Does germanium interact with radular morphogenesis and biomineralization in the limpet Lottia gigantea?

Specimens of Lottia gigantea were incubated in germanium enriched seawater [( Ge]/[Si] = 0.2-783) for 1-8 days. The siliceous radulae were examined histologically. No visible changes, degenerations or deformations were found in all 62 experimental radulae, although germanium is known to be a competitive inhibitor of silicon. In high concentrations, germanium was toxic to the limpets and killed them. Germanium was incorporated into the radular teeth in a distribution similar to silicon. Two suggestions are discussed for the apparent noninhibitory result.     

The ratio of germanium to silicon in plant phytoliths: quantification of biological discrimination under controlled experimental conditions

Slight differences in the chemical behavior of germanium (Ge) and silicon (Si) during soil weathering enable Ge/Si ratios to be used as a tracer of Si pathways. Mineral weathering and biogenic silicon cycling are the primary modifiers of Ge/Si ratios, but knowledge of the biogenic cycling component is based on relatively few studies. We conducted two sets of greenhouse experiments in order to better quantify the range and variability in Ge discrimination by plants. Graminoid species commonly found in North American grassland systems, Agropyron smithii, Schizachyrium scoparium, and Andropogon gerardii were grown under controlled hydroponic environmental conditions. Silicon leaf contents were positively correlated with solution Si and ambient temperature but not with nutrient solution pH, electrical conductivity, or species. The Ge/Si ratio incorporated into phytoliths shows a distribution coefficient [(Ge/Si)_phytolith/(Ge/Si)_solution] of about 0.2 and is remarkably invariant between species, photosynthetic pathway, and solution temperature. Ge seems to be discriminated against during the uptake and translocation of Si to the opal deposition sites by about a factor of five. In the second experiment, a wider range of graminoid species (Agropyron smithii, Bouteloua gracilis, Buchloe dactyloides, Oryzopsis hymenoides, Schizachyrium scoparium and Andropogon gerardii) were grown in two different soil mediums. Plant phytoliths showed a distribution factor of about 0.4 for field grown grasses, and 0.6 for potting soil grown grasses with no clear trends among the species. Evidence of the direction and degree of biological Ge discrimination during plant uptake provides a geochemical finger print for plants and improves the utility of Ge/Si ratios in studies of terrestrial weathering and links between Si cycles in terrestrial and marine systems.     

Subcellular localization of silicon and germanium in grass root and leaf tissues by SIMS: evidence for differential and active transport

Silicon transport and incorporation into plant tissue is important to both plant physiological function and to the influence plants have on ecosystem silica cycling. However, the mechanisms controlling this transport have only begun to be explored. In this study, we used secondary ion mass spectrometry (SIMS) to image concentrations of Si in root and shoot tissues of annual blue grass (Poa annua L.) and orchard grass (Dactylis glomerata L.) with the goal of identifying control points in the plant silica uptake pathway. In addition, we used SIMS to describe the distributions of germanium (Ge); the element used to trace Si in biogeochemical studies. Within root tissue, Si and Ge were localized in the suberized thick-walled region of endodermal cells, i.e. the proximal side of endodermal cells which is in close association to the casparian strip. In leaves, Si was present in the cell walls, but Ge was barely detectable. The selective localization of Si and Ge in the proximal side of endodermal cell walls of roots suggests transport control is exerted upon Si and Ge by the plant. The absence of Si in most root cell walls and its presence in the cell walls of leaves (in areas outside of the transpiration terminus) suggests modifications in the chemical form of Si to a form that favors Si complexation in the cell walls of leaf tissue. The low abundance of Ge in leaf tissue is consistent with previous studies that suggest preferential transport of Si relative to Ge.     

Putative silicon transport vesicles in the cytoplasm of the diatom Synedra acus during surge uptake of silicon

We studied the growth of the araphid pennate diatom Synedra acus subsp. radians (Kützing) Skabichevskii using a fluorescent dye N ¹,N ³-dimethyl-N ¹-(7-nitro-2,1,3-benzoxadiazol-4-yl)propane-1,3-diamine (NBD-N2), which stains growing siliceous frustules but does not stain other subcellular organelles. We used a clonal culture of S. acus that was synchronized by silicon starvation. Epifluorescence microscopy was performed in two different ways with cells stained by the addition of silicic acid and the dye. Individual cells immobilized on glass were observed during the first 15–20 min following the replenishment of silicic acid after silicon starvation. Alternatively, we examined cells of a batch culture at time intervals during 36 h after the replenishment of silicic acid using fluorescence and confocal microscopy. The addition of silicic acid and NBD-N2 resulted in the rapid (1–2 min) formation of several dozen green fluorescent submicrometer particles (GFSPs) in the cytoplasm, which was accompanied by the accumulation of fluorescent silica inside silica deposition vesicles (SDVs) along their full length. In 5–15 min, GFSPs disappeared from the cytoplasm. Mature siliceous valves were formed within the SDVs during the subsequent 14–16 h. In the next 8–10 h, GFSPs appeared again in the cytoplasm of daughter cells. The data obtained confirm observations about the two-stage mechanism of silicon assimilation, which includes rapid silicon uptake (surge uptake) followed by slow silica deposition. It is likely that the observed GFSPs are silicon transport vesicles, which were first proposed by Schmid and Schulz in (Protoplasma 100:267–288, 1979).     

Iron incorporation in biosilica of the marine diatom <Emphasis Type="Italic">Stephanopyxis</Emphasis> <Emphasis Type="Italic">turris</Emphasis>: dispersed or clustered?

Iron incorporation into diatom biosilica was investigated for the species Stephanopyxis turris. It is known that several “foreign” elements (e.g., germanium, titanium, aluminum, zinc, iron) can be incorporated into the siliceous cell walls of diatoms in addition to silicon dioxide (SiO₂). In order to examine the amount and form of iron incorporation, the iron content in the growth medium was varied during cultivation. Fe:Si ratios of isolated cell walls were measured by ICP-OES. SEM studies were performed to examine of a possible influence of excess iron during diatom growth upon cell wall formation. The chemical state of biosilica-attached iron was characterized by a combination of infrared, ²⁹Si MAS NMR, and EPR spectroscopy. For comparison, synthetic silicagels of variable iron content were studied. Our investigations show that iron incorporation in biosilica is limited. More than 95% of biosilica-attached iron is found in the form of iron clusters/nanoparticles. In contrast, iron is preferentially dispersedly incorporated within the silica framework in synthetic silicagels leading to Si–O–Fe bond formation.     

Silicon uptake and metabolism of the marine diatom Thalassiosira pseudonana: Solid-state 29Si NMR and fluorescence microscopic studies

Uptake and metabolism of silicon by diatoms are studied by the combined use of solid-state 29Si NMR spectroscopy and confocal laser fluorescence microscopy especially with respect to the presence and nature of an intracellular silicon-storage pool. Cells of the marine diatom Thalassiosira pseudonana were synchronized by silicon starvation and frozen without any freeze-drying or chemical treatment in order to analyze integer and unmodified diatoms. The frozen samples were investigated by solid-state 29Si NMR spectroscopy to identify potential silica precursors. The developmental state of the cell culture and the formation of new siliceous girdle bands and valves were monitored by laser fluorescence microscopic studies. A comparison of fluorescence microscopic and NMR data allows the assignment of NMR spectra to the various developmental stages of the dividing diatom cells. A detailed analysis of solid-state 29Si NMR spectra suggests that the silicon-storage pool-if present-consists of four-coordinated, condensed silicon; possibly a silica sol.     

Fine Structure of a Silica-Biomineralizing Testate Amoeba,Netzelia tuberculata1

The fine structure of the cytoplasm and the intracytoplasmic origin of siliceous granules and surrounding cement plaques used in constructing the shell wall of Netzelia tuberculata are described. These organisms construct their test from biogenic siliceous particles and sand grains or other foreign particles (including starch grains apparently from algal prey) coated with biogenic silica. The smooth surface texture of the grains, compared to those of other particle-gathering testate amoebae, can be expalained by the deposition of a thin surface layer of silica on the foreign particles incorporated into the wall.     

Germanium does not substitute for boron in cross-linking of rhamnogalacturonan II in pumpkin cell walls

Boron (B)-deficient pumpkin (Cucurbita moschata Duchesne) plants exhibit reduced growth, and their tissues are brittle. The leaf cell walls of these plants contain less than one-half the amount of borate cross-linked rhamnogalacturonan II (RG-II) dimer than normal plants. Supplying germanium (Ge), which has been reported to substitute for B, to B-deficient plants does not restore growth or reduce tissue brittleness. Nevertheless, the leaf cell walls of the Ge-treated plants accumulated considerable amounts of Ge. Dimeric RG-II (dRG-II) accounted for between 20% and 35% of the total RG-II in the cell walls of the second to fourth leaves from Ge-treated plants, but only 2% to 7% of the RG-II was cross-linked by germanate (dRG-II-Ge). The ability of RG-II to form a dimer is not reduced by Ge treatment because approximately 95% of the monomeric RG-II generated from the walls of Ge-treated plants is converted to dRG-II-Ge in vitro in the presence of germanium oxide and lead acetate. However, dRG-II-Ge is unstable and is converted to monomeric RG-II when the Ge is removed. Therefore, the content of dRG-II-Ge and dRG-II-B described above may not reflect the actual ratio of these in muro. (10)B-Enriched boric acid and Ge are incorporated into the cell wall within 10 min after their foliar application to B-deficient plants. Foliar application of (10)B but not Ge results in an increase in the proportion of dRG-II in the leaf cell wall. Taken together, our results suggest that Ge does not restore the growth of B-deficient plants.     

SILICON DEPOSITION DURING THE CELL CYCLE OF THALASSIOSIRA WEISSFLOGII (BACILLARIOPHYCEAE) DETERMINED USING DUAL RHODAMINE 123 AND PROPIDIUM IODIDE STAINING1

The relatively non-toxic dye, rhodamine 123 (R123), was incorporated into the frustule of Thalassiosira weissflogii Grun. clone ACTIN in direct proportion to biogenic silica (BSi). R123 was used together with the DNA stain propidium iodide to track and quantify Si deposition during the cell cycle of T. weissflogii using flow cytometry. Silicon deposition was not continuous through the cell cycle. Deposition of the valves occurred during M phase. The hypocingulum was largely deposited during G1 with some suggestion of minor girdle band deposition during G2. Silicon deposition did not occur during S phase. Assuming that a complete frustule consists of an epivalve, epicingulum, hypocingulum, and hypovalve, then 40% of cellular BSi was contained within the cingulum of T. weissflogii with 60% present in the valves. These percentages correspond to 0.38 pmol Si in the two cingula and 0.57 pmol Si in the valves. Temporal differences in the timing of silicic acid uptake and deposition during the cell cycle of T. weissflogii suggested that deposition of both the new valves and the cingulum is supported by an internal pool of dissolved Si acquired during G2.     

The effects of silicate depletion and subsequent replenishment on the cytoplasmic fine structure of the silica-secreting testate amoeba Netzelia tuberculata in laboratory culture

In the absence of silicate in the growth medium, Netzelia tuberculata cells withdraw their feeding lobopodia, become quiescent, and cease to divide. Upon replenishment of silicate, growth resumes within 18–24 hours. Cytoplasmic changes produced by a low silicate medium result in a zonal arrangement, with siliceous particles at the outer periphery of the cytoplasm in a region rich in Golgi bodies (Region A), a more centrally located layer containing endoplasmic reticulum, lipid reserves, and finely granular cytoplasm (Region B), and a region of partially digested food and waste material fringed by fine rhizopodia extending into the central space of the test (Region C). The reserve siliceous particles in the outer peripheral cytoplasm are foreign particles that contain a fragile deposit of silica and appear to be incomplet. This may be a mechanism for conserving silica in the low-silicate medium by coating particles instead of making particles of solid silica de novo. Upon addition of silicate to the growth medium, new siliceous particles are synthesized within vacuoles in the region of the Golgi apparatus within 2–18 hours. Vacuoles containing fine silica deposits, characteristic of new particle production, are surrounded by Golgi-derived vesicles previously shown to be a source of membrane for the silica-secreting vacuoles. The newly synthesized particles are solid silica as is characteristic of de novo secreted test particles, in contrast to the numerous silica-coated foreign bodies found in quiescent cells produced in low-silicate medium.     

MICROMORPHOGENESIS DURING DIATOM WALL FORMATION PRODUCES SILICEOUS NANOSTRUCTURES WITH DIFFERENT PROPERTIES1

Micromorphogenesis within the silica deposition vesicle (SDV) of the diatom Pinnularia viridis (Nitzsh) Ehrenb. resulted in distinct silica nanostructures and layers within forming valves and girdle bands. These siliceous components were similarly disclosed following alkaline etching of mature valves/girdle bands, where their different susceptibilities to dissolution over time resulted from apparent differences in silica density and/or chemistry. The bulk of silica appeared to be deposited at the interface of the forming valve or girdle band with the silicalemma and occurred by the outward expansion of microfibrils of silica that aligned perpendicularly to the silicalemma. Microfibrils originated from both sides of the “silica lamella,” the first nanostructure formed within the SDV, and several silica species of distinct nanostructure and density resulted, including distinctive inner and outermost silica “coverings” of mature valves/girdle bands and the central and terminal nodules. Not all silica deposition and micromorphogenesis occurred in contact with the expanding silicalemma, but was somehow directed within the SDV cavity, and resulted in the distinct silica layers that lined the raphe fissures and poroids. Following alkaline etching, the inner surfaces of valves/girdle bands, as well as the silica layers lining the raphes, poroids, and slits, were determined to be significantly more resistant to alkaline etching than the exterior surfaces, while the outer silica coating and the nodules were quickly dissolved. The processes of micromorphogenesis must have exerted precise control over the chemical nature of the silica formed at different positions within the SDV and affected the overall structure and function of the diatom wall.     

DIATOM MINERALIZATION OK SILICIC ACID. I Si(OH)4 TRANSPORT CHARACTERISTICS IN NAVICULA PELLICULOSA

Silicic acid transport was studied in the photosynthetic diatom Navicula pelliculosa (Bréb.) Hilse using [⁶⁸Ge] germanic acid (⁶⁸Ge(OH)₄) as a tracer of silicic acid (Si(OH)₄). The initial uptake rate of Si(OH)₄ was dependent on cell number, pH, temperature, light and was promoted by certain monovalent cations in the medium. Na⁺ was more effective than K⁺, whereas Li⁺ and NH⁺₄ were ineffective at promoting uptake. Uncouplers and inhibitors of oxidative phosphorylation and of photophosphorylation reduced uptake by 40–99% of control values. Uptake was also especially sensitive to the sulfhydryl blocking agents at 10^?5 M and to the ionophorous compound valinomycin (10^?7 M) which inhibited uptake by 82%. The Si(OH)₄ transport system displayed Michaelis-Menten-type saturation kinetics with kinetic parameters of K_S= 4.4 p. mol Si(OH)₄· 1^?1, V_max= 334 pmol Si(OH)₄· 10⁶ cells^?1· min^?1. Calculations of the acid soluble silicic acid pool size based on 60 s uptake at 20 μM Si(OH)₄ suggested that intracellular levels of Si could reach 20 mM and as much as 5 mM could exist as free silicic acid, representing maintenance of a 250-fold concentration gradient compared with the medium. Efflux from preloaded cells was dependent on temperature and the Si(OH)₄ concentration of the external medium. In the presence of 100 μMM “cold” Si(OH)₄, approximately 30% of the Si(OH)₄ in preloaded cells was exchanged in 20 min. The initial uptake rate of Si(OH)₄ in logarithmic phase cells was constant, but the uptake rate increased in a linear fashion for 6 h in stationary phase cells. These results suggest that the first step in silica mineralization by diatoms is the active transmembrane transport of Si(OH)₄ by an energy dependent, saturable, membrane-carrier mechanism which requires the monovalent cations Na⁺ and K⁺ and is sensitive to sulfhydryl blocking agents. Silicic acid transport activity also appears to be regulated during different growth stages of the diatom.     

Silicon uptake in diatoms revisited: a model for saturable and nonsaturable uptake kinetics and the role of silicon transporters

The silicic acid uptake kinetics of diatoms were studied to provide a mechanistic explanation for previous work demonstrating both nonsaturable and Michaelis-Menten-type saturable uptake. Using (68)Ge(OH)(4) as a radiotracer for Si(OH)(4), we showed a time-dependent transition from nonsaturable to saturable uptake kinetics in multiple diatom species. In cells grown under silicon (Si)-replete conditions, Si(OH)(4) uptake was initially nonsaturable but became saturable over time. Cells prestarved for Si for 24 h exhibited immediate saturable kinetics. Data suggest nonsaturability was due to surge uptake when intracellular Si pool capacity was high, and saturability occurred when equilibrium was achieved between pool capacity and cell wall silica incorporation. In Thalassiosira pseudonana at low Si(OH)(4) concentrations, uptake followed sigmoidal kinetics, indicating regulation by an allosteric mechanism. Competition of Si(OH)(4) uptake with Ge(OH)(4) suggested uptake at low Si(OH)(4) concentrations was mediated by Si transporters. At high Si(OH)(4), competition experiments and nonsaturability indicated uptake was not carrier mediated and occurred by diffusion. Zinc did not appear to be directly involved in Si(OH)(4) uptake, in contrast to a previous suggestion. A model for Si(OH)(4) uptake in diatoms is presented that proposes two control mechanisms: active transport by Si transporters at low Si(OH)(4) and diffusional transport controlled by the capacity of intracellular pools in relation to cell wall silica incorporation at high Si(OH)(4). The model integrates kinetic and equilibrium components of diatom Si(OH)(4) uptake and consistently explains results in this and previous investigations.     

Germanium: environmental occurrence, importance and speciation

This review discusses the various aspects of the bio-geochemistry of germanium, and of its technological, economical and environmental importance. Despite the relatively low annual production and consumption of this semi-metal (ca. 80 metric tons/a) there are important technological applications of this element in the semiconductor, infrared optics and fibre optics/telecommunication industries. A small, but not insignificant fraction of this element is used for the production of pharmaceuticals and nutritional supplements, although its actual merits have not been fully demonstrated yet, while they are opposed to chronic toxicity of the element when being administrated at relatively high doses for an extended period of time. Neither the exact mechanism of action in the case of cancer treatment or the treatment of infectious diseases is known, nor the reason for the toxicity of inorganic species of this element. In plants, Ge can partially substitute for B in the case of boron deficiency, although deficiency symptoms are still seen with a lag period of ca. one to three weeks. In biogeochemical respect, germanium and silicon react very similar, as if Ge were a very heavy isotope of Si. Their molar ratio is typically in the order of 0.6 × 10⁻⁶, with significant deviations only where germanium is complexed and transported, e.g., by humic-rich waters. Germanium is a very conservative element in biogeochemical terms: It hardly shows involvement in any biogeochemical reaction cycles and is mainly present in the form of complexes or hydroxo-compounds of the tetravalent germanium. The only naturally occurring organogermanium compounds are mono- and dimethylgermanium which are believed to be formed by microbiological activity in continental zones containing Ge-rich minerals, and then are leached into rivers, and finally into the open sea. It becomes evident that, although very sophisticated technological uses of germanium exist, a better understanding of its biogeochemical importance, cycling and reactivity must still be developed.     

Interaction of germanium (Ge) with biosilicification in the freshwater sponge Ephydatia mülleri: evidence of localized membrane domains in the silicalemma

In the presence of germanium (Ge) the needle-shaped silica spicules of the freshwater sponge Ephydatia m ulleri are very short and thin and possess bulbs with large spines. SEM-coupled X-ray analyses confirm the incorporation of Ge into the silica. A small number of bulbs are susceptible to erosion by HNO3 and hypochlorite and although the chemical basis of such erosion is presently unknown it suggests the presence of an organic matrix within the bulbs and/or an incomplete polymerization of the silica. Addition of Ge to control media in which silicification is newly initiated increases the incidence of erosion and results in centrally located eroded areas of the silica and discontinuities in its deposition. Removal of Ge from such newly forming structures results in a partial recovery of normal morphology (spine development and thickening of the silica) but only in the central region surrounding the bulbs. Both results establish the presence of a central, active region for silicification and further support the view that there is a distal spreading, away from this center, of transported forms of silica. Secondary centers may also be present. The newly assembled organic core of control structures is associated with tubular elements possibly derived from the surrounding membrane. In such newly silicifying structures the spicule tips contain oriented material in the form of "rays." Both of these new observations increase the likelihood of the presence of an organic matrix within the silica.     

Synthesis,characterization, and photoluminescence property of Nd–TUD‐1

Here, five different samples of neodymium (Nd) incorporated 3D‐mesoporous siliceous materials were fabricated using a single‐step hydrothermal technique. Typically, all samples were subjected to several qualitative elemental and quantitative analyses such as X‐ray diffraction, N₂‐adsorption/desorption, scanning electron microscopy, energy dispersive X‐ray, mapping, high resolution transmission electron microscopy, diffuse reflectance ultraviolet–visible, and Raman spectroscopy. The characterization results showed that at small loading of Nd (i.e. Si/Nd < 20), only isolated centres of trivalent neodymium ions were tetrahedrally coordinated in the TUD‐1 matrix. However, with increasing neodymium loading, additional nanoparticles of neodymium oxide with size 10–20 nm were embedded into silica host pores. Detailed photoluminescence (PL) analysis of all samples was carried out by recording the emission profiles at two diverse excitation wavelengths, 333 and 343 nm, to understand the effect of the Nd³⁺ environment on the PL emission spectra with special attention to the area between 400 and 600 nm. Most importantly, different peaks of the emission spectrum of each sample exhibited a distinct shape based on the Nd³⁺ environment. This performance was superior evidence that PL can be applied as a simple and efficient characterization tool to understand the nature of Nd³⁺ ion linkage with a silica matrix.     

Role of silicon in diatom metabolism

1. In silicic acid-starved cells of the diatom Nitzschia alba, ⁶⁸Ge(OH)₄ is transported against a concentration gradient, leading to intracellular concentrations of germanic acid up to 3500 times greater than the exogenous concentrations. The accumulated substrate is osmotically active, as determined by its efflux into germanic acid-free medium.
2. Metabolic energy is required for Ge(OH)₄ transport, since uptake is completely inhibited by 1 mM DNP, 5×10^-2 M sodium azide or 1 mM iodacetamide, and is strongly inhibited by CCCP and antimycin A. Inhibition of protein synthesis with 20 μg/ml cycloheximide does not affect the initial velocity of transport, but strongly reduces the steady state intracellular concentration.
3. A double reciprocal plot of uptake velocity versus substrate concentration yields a biphasic curve. The kinetic data are consistent with the interpretation that N. alba has two transport systems for germanic acid; a high affinity-low capacity (K _s=0.36 μM; V _max 1.2 μmoles/10⁸ cells/min) system and a low affinity-high capacity (K _s=5 μM; V _max 6.2 μmoles/10⁸ cells/min) system.
4. The implications of these findings for silicic acid transport and metabolism in N. alba are discussed.

     

Dissection of the frustules of the diatom Synedra acus under the action of picosecond impulses of submillimeter laser irradiation

Diatom algae realize highly intriguing processes of biosynthesis of siliceous structures in living cells under moderate conditions. Investigation of diatom physiology is complicated by frustule (siliceous exoskeleton). Frustules consist of valves and girdle bands which are adhered to each other by means of organic substances. Removal of the frustule from the lipid membrane of diatom cells would open new possibilities for study of silicon metabolism in diatoms. We found that submillimeter laser irradiation produced by a free-electron laser causes splitting of diatom frustules without destruction of cell content. This finding opens the way to direct study of diatom cell membrane and to isolation of cell organelles, including silica deposition vesicles. We suppose that the dissection action of the submillimeter irradiation results from unusual ultrasonic waves produced by the short (30–100 ps) but high-power (1 MW) terahertz laser impulses at 5.6 MHz frequency.