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N Metabolism (n + metabolism)
Selected AbstractsVariability of Endotoxin Expression in Bt Transgenic CottonJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 1 2007H. Z. Dong Abstract Transgenic cotton expressing Bt (Bacillus thuringiensis) toxins is currently cultivated on a large commercial scale in many countries, but observations have shown that it behaves variably in toxin efficacy against target insects under field conditions. Understanding of the temporal and spatial variation in efficacy and the resulting mechanisms is essential for cotton protection and production. In this review, we summarize current knowledge on variability in Bt cotton efficacy, in particular on the induced variability by environmental stresses. We also discuss the resulting mechanisms and the countermeasures for the inconsistence in efficacy in Bt cotton. It is indicated that insecticidal protein content in Bt cotton is variable with plant age, plant structure or under certain environmental stresses. Variability in Bt cotton efficacy against target insect pests is mainly attributed to the changes in Bt protein content, but physiological changes associated with the production of secondary compounds in plant tissues may also play an important role. Reduction of Bt protein content in late-season cotton could be due to the overexpression of Bt gene at earlier stages, which leads to gene regulation at post-transcription levels and consequently results in gene silencing at a later stage. Methylation of the promotor may be also involved in the declined expression of endotoxin proteins. As a part of total protein, the insecticidal protein in plant tissues changes its level through inhibited synthesis, degradation or translocation to developing plant parts, particularly under environmental stresses, thus being closely correlated to N metabolism. It can be concluded that developing new cotton varieties with more powerful resistance, applying certain plant growth regulators, enhancing intra-plant defensive capability, and maintenance of general health of the transgenic crop are important in realizing the full transgenic potential in Bt cotton. [source] RESPONSE OF GLUTAMINE SYNTHETASE GENE TRANSCRIPTION AND ENZYME ACTIVITY TO EXTERNAL NITROGEN SOURCES IN THE DIATOM SKELETONEMA COSTATUM (BACILLARIOPHYCEAE),JOURNAL OF PHYCOLOGY, Issue 1 2005Misaki Takabayashi To understand the enhanced ability of marine diatoms to assimilate nitrogen (N), we measured changes in the transcript abundance and enzyme activity of glutamine synthetase (GS), one of the key enzymes that link carbon (C) and N metabolism, in the common diatom Skeletonema costatum (Greville) Cleve. Transcript abundance of glnII (the gene that encodes the GSII isoenzyme), measured by quantitative reverse transcriptase-PCR, and total GS activity increased 2 to 3.5 times above background in the cells taking up nitrate (NO3,) but not the cells taking up ammonium (NH4+). A background level of glnII mRNA was maintained at a steady level up to 15 days of N starvation before decreasing to below detection after 21 days. These results confirm that transcription of glnII is induced to assimilate NH4+ derived from reduction of NO3,. Because of this role of GSII in diatoms assimilating NH4+ derived from NO3, reduction rather than from the environmental NH4+, quantification of glnII mRNA promises to be a useful indication of new production by phytoplankton. [source] Seasonal variations in nitrate reductase activity and internal N pools in intertidal brown algae are correlated with ambient nitrate concentrationsPLANT CELL & ENVIRONMENT, Issue 6 2007ERICA B. YOUNG ABSTRACT Nitrogen metabolism was examined in the intertidal seaweeds Fucus vesiculosus, Fucus serratus, Fucus spiralis and Laminaria digitata in a temperate Irish sea lough. Internal NO3 - storage, total N content and nitrate reductase activity (NRA) were most affected by ambient NO3 - , with highest values in winter, when ambient NO3 - was maximum, and declined with NO3 - during summer. In all species, NRA was six times higher in winter than in summer, and was markedly higher in Fucus species (e.g. 256 ± 33 nmol NO3 - min,1 g,1 in F. vesiculosus versus 55 ± 17 nmol NO3 - min,1 g,1 in L. digitata). Temperature and light were less important factors for N metabolism, but influenced in situ photosynthesis and respiration rates. NO3 - assimilating capacity (calculated from NRA) exceeded N demand (calculated from net photosynthesis rates and C : N ratios) by a factor of 0.7,50.0, yet seaweeds stored significant NO3 - (up to 40,86 µmol g,1). C : N ratio also increased with height in the intertidal zone (lowest in L. digitata and highest in F. spiralis), indicating that tidal emersion also significantly constrained N metabolism. These results suggest that, in contrast to the tight relationship between N and C metabolism in many microalgae, N and C metabolism could be uncoupled in marine macroalgae, which might be an important adaptation to the intertidal environment. [source] Impact of nitrate supply in C and N assimilation in the parasitic plant Striga hermonthica (Del.) Benth (Scrophulariaceae) and its host Sorghum bicolor L.PLANT CELL & ENVIRONMENT, Issue 4 2006P. SIMIER ABSTRACT The threshold of tolerance for nitrate of the parasitic weed Striga hermonthica (Del.) Benth and the host plant Sorghum bicolor L. was determined by estimating the impact of increasing nitrate loads on plant growth and various parameters of C and N assimilation. Nitrate supply improved chlorophyll (Chl) content and photosystem II (PSII) photochemistry of infected S. bicolor that, in comparison to S. hermonthica, displayed a low imbalance between C and N assimilation when nitrate was supplied up to 1500 mg N per plant. Indeed, nitrate supplies increased strongly the leaf N:C ratio of the parasite. The higher nitrate load induced strong accumulation of nitrate, nitrite and ammonium, and consequently the death of S. hermonthica. Nevertheless, lower nitrate loads (up to 500 mg N per S. bicolor in this study) promoted leaf expansion, PSII photochemistry and N metabolism of S. hermonthica mature (M) plants, as attested by the significant rise in soluble protein and free amino-acid contents. Following these N supplies, the nitrate tolerance of S. hermonthica was correlated with an increase in PSII activity and a high incorporation of N excess into asparagine. This confirmed the central role of asparagine in the N metabolism of S. hermonthica, although this detoxification pathway was insufficient to limit ammonium accumulation under higher nitrate loads. [source] Metabolic profiling as a tool for understanding defense response of Taxus Cuspidata cells to shear stressBIOTECHNOLOGY PROGRESS, Issue 5 2009Pei-Pei Han Abstract To obtain a better understanding of responsive mechanism of plant cells in response to hydrodynamic mechanical stress, a metabolic profiling approach was used to profile metabolite changes of Taxus cuspidata cells under laminar shear stress. A total of 65 intracellular metabolites were identified and quantified, using gas chromatography coupled to time-of-flight mass spectrometry. Potential biomarkers were found by the principal component analysis as well as partial least squares combined with variable influence in the projection. Trehalose, sorbitol, ascorbate, sucrose, and gluconic acid were mainly responsible for the discrimination between shear stress induced cells and control cells. Further analysis by mapping measured metabolite concentrations onto the metabolic network revealed that shear stress imposed restrictions on primary metabolic pathways by inhibiting tricarboxylic acid cycle, glycolysis, and N metabolism. To adapt to the shear condition, cells responded by starting defensive programs. These defensive programs included coinduction of glycolysis and sucrose metabolism, accumulation of compatible solutes, and antioxidative strategy. A strategy of defense mechanisms at the level of metabolites for T. cuspidata cells when challenged with the shear stress was proposed. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] UNCOUPLING OF SILICON COMPARED WITH CARBON AND NITROGEN METABOLISMS AND THE ROLE OF THE CELL CYCLE IN CONTINUOUS CULTURES OF THALASSIOSIRA PSEUDONANA (BACILLARIOPHYCEAE) UNDER LIGHT, NITROGEN, AND PHOSPHORUS CONTROL1JOURNAL OF PHYCOLOGY, Issue 5 2002Pascal Claquin The elemental composition and the cell cycle stages of the marine diatom Thalassiosira pseudonana Hasle and Heimdal were studied in continuous cultures over a range of different light- (E), nitrogen- (N), and phosphorus- (P) limited growth rates. In all growth conditions investigated, the decrease in the growth rate was linked with a higher relative contribution of the G2+M phase. The other phases of the cell cycle, G1 and S, showed different patterns, depending on the type of limitation. All experiments showed a highly significant increase in the amount of biogenic silica per cell and per cell surface with decreasing growth rates. At low growth rates, the G2+M elongation allowed an increase of the silicification of the cells. This pattern could be explained by the major uptake of silicon during the G2+M phase and by the independence of this process on the requirements of the other elements. This was illustrated by the elemental ratios Si/C and Si/N that increased from 2- to 6-fold, depending of the type of limitation, whereas the C/N ratio decreased by 10% (E limitation) or increased by 50% (P limitation). The variations of the ratios clearly demonstrate the uncoupling of the Si metabolism compared with the C and N metabolisms. This uncoupling enabled us to explain that in any of the growth condition investigated, the silicification of the cells increased at low growth rates, whereas carbon and nitrogen cellular content are differently regulated, depending of the growth conditions. [source] | ||||||||||