Influence of temperature and salinity on carbon and nitrogen content in Dunaliella viridis teodoresco under nitrogen sufficiency

Cell carbon and nitrogen in D. viridis are strongly dependent on the culturing conditions. Both elements increase with increasing salinity. At 31°C cell carbon is maximum and cell nitrogen minimum. This temperature was described previously (Jiménez, C., Niell, F. X. & Fernandez, J. A. (1990). Hydrobiologia, 197, 165-72) as the optimal one for achieving the maximum oxygen evolution. These results point out a possible competence for the reducing power during carbon and nitrogen assimilation processes, and under conditions of high photosynthesis (carbon assimilation) there is a partial inhibition of nitrate reduction, making C:N ratio maximum under conditions of maximum net photosynthesis.The study of cell glycerol, nitrate, structural proteins and free amino acids indicates that all of these solutes accumulate in the cells as a result of the high salinity adaptation.     

ZnCl2-Modified Activated Carbon from Biomass Coir Pith for the Removal of 2-Chlorophenol by Adsorption Process

Coir pith, a waste biomass, from coconut coir industry was used to prepare activated carbon with ZnCl₂ and employed for the removal of 2-chlorophenol (2-CP) from aqueous solution and wastewater. Zinc chloride–activated coir pith carbon (ZnCPC) was prepared by mixing coir pith with ZnCl₂ in the ratio 2:1 and carbonized at 700°C for 1 h. ZnCPC was characterized using standard physicochemical methods, Brunaver, Emmett, and Teller (BET) surface area, and scanning electron microscopy (SEM) studies. Batch mode adsorption studies were carried out to evaluate the effect of contact time, initial concentration, adsorbent dose, pH, and temperature. The Langmuir adsorption capacity Q ₀ was found to be 149.3 mg g^?1. Kinetic studies showed that the adsorption obeyed second-order and Bangham's model. Equilibrium adsorption data fit better into Langmuir, Freundlich, and D-R isotherms. pH effect and desorption studies showed that ion-exchange mechanism was involved in the adsorption process. Effect of temperature was not significant. Quantitative removal of 2-CP from synthetic wastewater was also achieved. ZnCPC is economically effective compared to commercial activated carbon, because the raw material is abundantly and freely available and it can be used effectively in the treatment of water contaminated with 2-CP.     

Rapid cooling triggers forisome dispersion just before phloem transport stops

Phloem transport stops transiently within dicot stems that are cooled rapidly, but the cause remains unknown. Now it is known that (1) rapid cooling depolarizes cell membranes giving a transient increase in cytoplasmic Ca²⁺, and (2) a rise of free calcium triggers dispersion of forisomes, which then occlude sieve elements (SEs) of fabacean plants. Therefore, we compared the effects of rapid chilling on SE electrophysiology, phloem transport and forisomes in Vicia faba. Forisomes dispersed after rapid cooling with a delay that was longer for slower cooling rates. Phloem transport stopped about 20 s after forisome dispersion, and then transport resumed and forisomes re‐condensed within similar time frames. Transport interruption and forisome dispersion showed parallel behaviour – a cooling rate‐dependent response, transience and desensitization. Chilling induced both a fast and a slow depolarization of SE membranes, the electrical signature suggesting strongly that the cause of forisome dispersion was the transient promotion of SE free calcium. This apparent block of SEs by dispersed forisomes may be assisted by other Ca²⁺‐dependent sealing proteins that are present in all dicots.     

EVIDENCE OF AN ORGANIC MATRIX FROM DIATOM BIOSILICA1

Most biominerals appear to be composites of organic material and mineral. Whether biosilica is such a composite is unresolved because of a lack of evidence for such organic components. We present evidence that organic material exists within diatom biosilica and can be extracted using HF/NH₄F solutions from frustules isolated from Cyclotella meneghiniana Kütz and diatomaceous earth. To eliminate organic casing on the silicified frustules as a source of organic materials, the casing was removed by oxidation of frustules with NaOCl before extraction. The removal of the casing was confirmed in that oxidized frustules no longer displayed the ability to be stained with ruthenium red and fluorescamine. Frustules examined with EDXA showed an emission peak from sulfur before treatment but no peak following treatment, indicating that oxidation removed organic sulfur. The organic material obtained from extracts of fresh frustules contained both soluble and insoluble components. Only soluble material was evident in extracts from diatomaceous earth. The soluble material appears to contain glycoproteins with relatively high levels of serine and glycine. The soluble proteins from fresh frustules also appear to be phosphorylated. Indirect evidence is presented that suggests the soluble proteins may contain regions of primary structure enriched in anionic amino acids. The soluble extracts differ from general cell contents when the two fractions are compared, suggesting that frustules contain specialized organic material. The identification of silica-specific organic material suggests that mineralization in diatoms may be in part matrix-mediated.     

Carbon: terrestrial C4 plants

The carbon isotope composition of terrestrial C₄ plants depends on the primary carboxylation of phosphoenolpyruvate (PEP) and on the diffusion of CO₂ to the carboxylation sites, but is also influenced by the final carboxylation of ribulose-1,5-bisphosphate (RuBP). Several models have been used for reproducing this complex situation. In the present review, a particular model is applied as a means to interpret the effects of environmental and genetically determined factors on carbon isotope discrimination during C₄ photosynthesis. As a new feature, the model considers four types of limitation of the overall CO₂ assimilation rate. Both carboxylation reactions are assumed to be limited by either maximum enzyme activity or maximum substrate regeneration rate. The model is applied to experimental data on the effects of CO₂, irradiance and water stress on short-term discrimination by leaves of several C₄ species measured simultaneously with CO₂ gas exchange characteristics. In particular, different patterns of the influence of low irradiances on carbon isotope discrimination are interpreted as due to variations in that irradiance at which a transition from limitation by PEP regeneration rate and RuBP carboxylase activity to limitation by the regeneration rates of both substrates occurs. After discussing literature data on the effects of environmental conditions on carbon isotope discrimination by C₄ plants seasonal and developmental changes in carbon isotope composition, studies on the systematic and geographic distribution of C₄ plants, evolutionary and genetical aspects, and some ecological implications are reviewed.     

The carbon canopy economy of the association between cowpea and the parasitic angiosperm Striga gesnerioides

The association between the parasite Striga gesnerioides and cowpea (Vigna unguiculata) was investigated using measurements of growth and gas exchange together with calculations of the carbon budget of the association. Striga gesnerioides has a very low photosynthetic capacity coupled with high rates of respiration. Even at photosynthetic light saturation shoots exhibit no net carbon gain. Thus S. gesnerioides is highly dependent on its host for carbon as well as for water and inorganic solutes. It is estimated that 70% of the carbon transferred from host to parasite is used in parasite respiration. Infected cowpea had a lower photosynthetic capacity, at times less than half that of uninfected plants. Infection with S. gesnerioides reduced the growth of cowpea by 75%. Calculations indicate that the loss of carbon from the host by export to the parasite is more important than reduced photosynthetic capacity of the host in accounting for the observed growth reductions.     

Muscarinic receptor regulation of osmosensitive taurine transport in human SH-SY5Y neuroblastoma cells

The ability of G protein‐coupled receptors to regulate osmosensitive uptake of the organic osmolyte, taurine, into human SH‐SY5Y neuroblastoma cells has been examined. When monitored under isotonic conditions and in the presence of physiologically relevant taurine concentrations (1–100 μM), taurine influx was mediated exclusively by a Na⁺‐dependent, high‐affinity (K_m = 2.5 μM) saturable transport mechanism (V_max = 0.087 nmol/mg protein/min). Reductions in osmolarity of > 20% (attained under conditions of a constant NaCl concentration) resulted in an inhibition of taurine influx (> 30%) that could be attributed to a reduction in V_max, whereas the K_m for uptake remained unchanged. Inclusion of the muscarinic cholinergic agonist, oxotremorine‐M (Oxo‐M), also resulted in an attenuation of taurine influx (EC₅₀～0.7 μM). Although Oxo‐M‐mediated inhibition of taurine uptake could be observed under isotonic conditions (～25–30%), the magnitude of inhibition was significantly enhanced by hypotonicity (～55–60%), a result that also reflected a reduction in the V_max, but not the K_m, for taurine transport. Oxo‐M‐mediated inhibition of taurine uptake was dependent upon the availability of extracellular Ca²⁺ but was independent of protein kinase C activity. In addition to Oxo‐M, inclusion of either thrombin or sphingosine 1‐phosphate also attenuated volume‐dependent taurine uptake. The ability of Oxo‐M to inhibit the influx of taurine was attenuated by 4‐[(2‐butyl‐6,7‐dichloro‐2‐cyclopentyl‐2,3‐dihydro‐1‐oxo‐1H‐inden‐5‐yl)oxy]butanoic acid, an inhibitor of the volume‐sensitive organic osmolyte and anion channel. 4‐[(2‐Butyl‐6,7‐dichloro‐2‐cyclopentyl‐2,3‐dihydro‐1‐oxo‐1H‐inden‐5‐yl)oxy]butanoic acid also prevented receptor‐mediated changes in the efflux and influx of K⁺ under hypoosmotic conditions. The results suggest that muscarinic receptor activation can regulate both the volume‐dependent efflux and uptake of taurine and that these events may be functionally coupled.     

不同碳氮源对糙皮侧耳木质纤维素酶活性的影响

以糙皮侧耳Pleurotus ostreatus为材料,研究简单碳氮源及木质素纯品诱导条件对其木质纤维素酶活性的影响。结果表明,不同的碳源培养基和氮源培养基对糙皮侧耳漆酶活性、羧甲基纤维素酶活性和木聚糖酶活性均具有极显著的影响（P<0.001）,且对糙皮侧耳菌丝生物量也有极显著的影响（P<0.001）。以蔗糖作主要碳源诱导物时,有利于提高糙皮侧耳漆酶活性;以果糖作主要碳源诱导物时,有利于提高糙皮侧耳羧甲基纤维素酶活性和菌丝生物量的积累;以葡萄糖作主要碳源诱导物时,有利于提高糙皮侧耳木聚糖酶活性。以酵母浸粉作主要氮源诱导物时,有利于提高糙皮侧耳漆酶活性和菌丝生物量的积累;以硝酸钾作为主要氮源诱导物时,有利于提高糙皮侧耳羧甲基纤维素酶活性;以硫酸铵作为主要氮源诱导物时,有利于提高糙皮侧耳木聚糖酶活性。碱性木素的存在,有利于提高糙皮侧耳漆酶活性,但不利于菌丝生物量的积累。与此同时,碱性木素的存在对糙皮侧耳羧甲基纤维素酶和木聚糖酶活性并没有促进作用。     

Optimization of L-malic acid production by Aspergillus flavus in a stirred fermentor

Effects of various nutritional and environmental factors on the accumulation of organic acids (mainly L-malic acid) by the filamentous fungus Aspergillus flavus were studied in a 16-L stirred fermentor. Improvement of the molar yield (moles acid produced per moles glucose consumed) of L-malic acid was obtained mainly by increasing the agitation rate (to 350 rpm) and the Fe(z+) ion concentration (to 12 mg/L) and by lowering the nitrogen (to 271 mg/L) and phosphate concentrations (to 1.5 mM) in the medium. These changes resulted in molar yields for L-malic acid and total C(4) acids (L-malic, succinic, and fumaric acids) of 128 and 155%, respectively. The high molar yields obtained (above 100%) are additional evidence for the operation of part of the reductive branch of the tricarboxylic acid cycle in L-malic acid accumulation by A. flavus. The fermentation conditions developed using the above mentioned factors and 9% CaCO(3) in the medium resulted in a high concentration (113 g/L L-malic acid from 120 g/L glucose utilized) and a high overall productivity (0.59 g/L h) of L-malic acid. These changes in acid accumulation coincide with increases in the activities of NAD(+)-malate dehydrogenase, fumarase, and citrate synthase.