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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

During sexual differentiation, Chlamydomonas reinhardtii changes its chemotactic behavior in response to ammonium. Just like gamete formation, the change in chemotaxis mode is controlled by the sequential action of two environmental cues, removal of ammonium or nitrate from the medium and light. Thus, vegetative cells and mating incompetent pre-gametes, the latter being generated by nitrogen starvation in the dark, exhibit chemotaxis towards ammonium. Irradiation of pre-gametes results in a loss of chemotaxis and the gaining of mating competence. Incubation of these gametes in the dark resulted in their regaining chemotactic activity; re-illumination again resulted in its loss. Blue light was shown to be most effective in switching-off chemotaxis. RNA-interference strains with reduced levels of the blue-light receptor phototropin showed an attenuated inactivation of chemotaxis that could be partially compensated by the application of higher fluence rates, suggesting that these light responses are mediated by phototropin. The sharing of photoreceptor and signal transduction components as well as similar temporal patterns observed for changes in chemotaxis towards ammonium and gametic differentiation suggest an integration of the signaling pathways that control these two responses.
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PMID:Phototropin plays a crucial role in controlling changes in chemotaxis during the initial phase of the sexual life cycle in Chlamydomonas. 1504 70

We have quantitatively measured nitric oxide production in the leaves of Arabidopsis thaliana and Vicia faba by adapting ferrous dithiocarbamate spin tapping methods previously used in animal systems. Hydrophobic diethyldithiocarbamate complexes were used to measure NO interacting with membranes, and hydrophilic N-methyl-d-glucamine dithiocarbamate was used to measure NO released into the external solution. Both complexes were able to trap levels of NO, readily detectable by EPR spectroscopy. Basal rates of NO production (in the order of 1 nmol g(-) (1) h(-1)) agreed with previous studies. However, use of methodologies that corrected for the removal of free NO by endogenously produced superoxide resulted in a significant increase in trapped NO (up to 18 nmol g(-) (1) h(-1)). Basal NO production in leaves is therefore much higher than previously thought, but this is masked by significant superoxide production. The effects of nitrite (increased rate) and nitrate (decreased rate) are consistent with a role for nitrate reductase as the source of this basal NO production. However, rates under physiologically achievable nitrite concentrations never approach that reported following pathogen induction of plant nitric-oxide synthase. In Hibiscus rosa sinensis, the addition of exogenous nitrite generated sufficient NO such that EPR could be used to detect its production using endogenous spin traps (forming paramagnetic dinitrosyl iron complexes). Indeed the levels of this nitrosylated iron pool are sufficiently high that they may represent a method of maintaining bioavailable iron levels under conditions of iron starvation, thus explaining the previously observed role of NO in preventing chlorosis under these conditions.
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PMID:Endogenous superoxide production and the nitrite/nitrate ratio control the concentration of bioavailable free nitric oxide in leaves. 1505 52

Sulphate assimilation is an essential pathway being a source of reduced sulphur for various cellular processes and for the synthesis of glutathione, a major factor in plant stress defence. Many reports have shown that sulphate assimilation is well co-ordinated with the assimilation of nitrate and carbon. It has long been known that, during nitrate deficiency, sulphate assimilation is reduced and that the capacity to reduce nitrate is diminished in plants starved for sulphate. Only recently, however, was it shown that adenosine 5' phosphosulphate reductase (APR), the key enzyme of sulphate assimilation, is regulated by carbohydrates. In plants treated with sucrose or glucose APR was induced, whereas the activity was strongly reduced in plants grown in CO(2)-free air. The availability of cysteine is a crucial factor in glutathione synthesis, but an adequate supply of glutamate and glycine are also important. The molecular mechanisms for the co-ordination of S, N, and C assimilation are not known. O-acetylserine, a precursor of cysteine, was proposed to be the signal regulating sulphate assimilation, but most probably is not the outgoing signal to N and C metabolism. cDNA arrays revealed the induction of genes involved in auxin synthesis upon S-starvation, pointing to a possible role of phytohormones. Clearly, despite significant progress in understanding the regulation of sulphate assimilation and glutathione synthesis, their co-ordination with N and C metabolism achieved, and several potential signal molecules identified, present knowledge is still far from being sufficient.
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PMID:Control of sulphate assimilation and glutathione synthesis: interaction with N and C metabolism. 1528 42

Two types of small wastewater treatment systems were studied for their performance under normal conditions, including the hydraulic peak flows associated with small systems connected to just one house. Furthermore, the systems were subjected to a 7-day starvation period to simulate the effect of a holiday from home. The systems studied are (1) a combined submerged aerated filter-activated sludge system and (2) a rotating biological contactor system. Both the organic removal and the nitrification process were closely monitored. During normal operation, very good treatment results were achieved. The combined SAF-AS system realized 95% BOD removal, 88% COD removal and 94% NH4-N removal. The RBC system removed 92% of the BOD, 89% of the COD and 99% of the ammonium nitrogen. Both systems do not experience severe problems dealing with the lack of influent for a duration of seven days. The effluent concentrations did not change much, except for a small peak of nitrite which was present in all tests. However, both the ammonium oxidizing and the nitrite oxidizing bacterial populations were still active, as evidenced by the continued removal of ammonium and formation of nitrate.
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PMID:Performance of a submerged aerated filter and a rotating biological contactor under dynamic loading conditions. 1529 39

Full genome microarrays were used to assess transcriptional responses of Arabidopsis seedlings to changing external supply of the essential macronutrient potassium (K(+)). Rank product statistics and iterative group analysis were employed to identify differentially regulated genes and statistically significant coregulated sets of functionally related genes. The most prominent response was found for genes linked to the phytohormone jasmonic acid (JA). Transcript levels for the JA biosynthetic enzymes lipoxygenase, allene oxide synthase, and allene oxide cyclase were strongly increased during K(+) starvation and quickly decreased after K(+) resupply. A large number of well-known JA responsive genes showed the same expression profile, including genes involved in storage of amino acids (VSP), glucosinolate production (CYP79), polyamine biosynthesis (ADC2), and defense (PDF1.2). Our findings highlight a novel role of JA in nutrient signaling and stress management through a variety of physiological processes such as nutrient storage, recycling, and reallocation. Other highly significant K(+)-responsive genes discovered in our study encoded cell wall proteins (e.g. extensins and arabinogalactans) and ion transporters (e.g. the high-affinity K(+) transporter HAK5 and the nitrate transporter NRT2.1) as well as proteins with a putative role in Ca(2+) signaling (e.g. calmodulins). On the basis of our results, we propose candidate genes involved in K(+) perception and signaling as well as a network of molecular processes underlying plant adaptation to K(+) deficiency.
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PMID:The potassium-dependent transcriptome of Arabidopsis reveals a prominent role of jasmonic acid in nutrient signaling. 1534 84

Organic-acid secretion from higher plant roots into the rhizosphere plays an important role in nutrient acquisition and metal detoxification. In this study we report the electrophysiological characterization of anion channels in Arabidopsis (Arabidopsis thaliana) root epidermal cells and show that anion channels represent a pathway for citrate efflux to the soil solution. Plants were grown in nutrient-replete conditions and the patch clamp technique was applied to protoplasts isolated from the root epidermal cells of the elongation zone and young root hairs. Using SO4(2-) as the dominant anion in the pipette, voltage-dependent whole-cell inward currents were activated at membrane potentials positive of -180 mV exhibiting a maximum peak inward current (I(peak)) at approximately -130 mV. These currents reversed at potentials close to the equilibrium potential for SO4(2-), indicating that the inward currents represented SO4(2-) efflux. Replacing intracellular SO4(2-) with Cl- or NO3(-) resulted in inward currents exhibiting similar properties to the SO4(2-) efflux currents, suggesting that these channels were also permeable to a range of inorganic anions; however when intracellular SO4(2-) was replaced with citrate or malate, no inward currents were ever observed. Outside-out patches were used to characterize a 12.4-picoSiemens channel responsible for these whole-cell currents. Citrate efflux from Arabidopsis roots is induced by phosphate starvation. Thus, we investigated anion channel activity from root epidermal protoplasts isolated from Arabidopsis plants deprived of phosphate for up to 7 d after being grown for 10 d on phosphate-replete media (1.25 mm). In contrast to phosphate-replete plants, protoplasts from phosphate-starved roots exhibited depolarization-activated voltage-dependent citrate and malate efflux currents. Furthermore, phosphate starvation did not regulate inorganic anion efflux, suggesting that citrate efflux is probably mediated by novel anion channel activity, which could have a role in phosphate acquisition.
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PMID:Characterization of anion channels in the plasma membrane of Arabidopsis epidermal root cells and the identification of a citrate-permeable channel induced by phosphate starvation. 1556 25

The polyphosphate kinase gene from Pseudomonas aeruginosa was overexpressed in its native host, resulting in the accumulation of 100 times the polyphosphate seen with control strains. Degradation of this polyphosphate was induced by carbon starvation conditions, resulting in phosphate release into the medium. The mechanism of polyphosphate degradation is not clearly understood, but it appears to be associated with glycogen degradation. Upon suspension of the cells in 1 mM uranyl nitrate, nearly all polyphosphate that had accumulated was degraded within 48 h, resulting in the removal of nearly 80% of the uranyl ion and >95% of lesser-concentrated solutions. Electron microscopy, energy-dispersive X-ray spectroscopy, and time-resolved laser-induced fluorescence spectroscopy (TRLFS) suggest that this removal was due to the precipitation of uranyl phosphate at the cell membrane. TRLFS also indicated that uranyl was initially sorbed to the cell as uranyl hydroxide and was then precipitated as uranyl phosphate as phosphate was released from the cell. Lethal doses of radiation did not halt phosphate secretion from polyphosphate-filled cells under carbon starvation conditions.
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PMID:Uranyl precipitation by Pseudomonas aeruginosa via controlled polyphosphate metabolism. 1557 42

In Arabidopsis thaliana (L.) Heynh., AtPhr2 and AtNsr1 encode proteins with MYB-like and alpha-helical domains. They resemble CrPsr1, a nuclear-localized MYB protein that is critical for acclimation to phosphorous (P) starvation in the alga Chlamydomonas reinhardtii. Reverse transcription-polymerase chain reaction analysis of the first unique exons indicated that AtPhr2 mRNA increased as early as 6 h after P deprivation (-P), whereas nitrogen deprivation (-N) had no effect. The AtNsr1 mRNA level increased exclusively under -N, an increase first noted by 2 days in -N. In spite of P- and N-specific effects on expression of AtPhr2 and AtNsr1 there appeared to be P-N cross-talk at the whole-plant level. Total non-secreted acid phosphatase activity increased under both -P and -N within 2 days of deprivation. Further, the pho2-1/pho2-1 mutant, reported to be a phosphate accumulator, showed no increase in AtPhr2 mRNA in response to -P and a 70% reduction in the response of AtNsr1 mRNA to -N. Consistent with this pattern, there was no increase in acid phosphatase activity in pho2-1/pho2-1 plants deprived of P or N. However, when deprived of P, pho2-1/pho2-1 plants accumulated much higher levels of nitrate. T-DNA disruption of AtNsr1 resulted in altered expression of at least one nitrate transporter (AtNRT2.5). Further evidence of cross-talk between N and P responses was altered expression of N-responsive genes in pho2-1/pho2-1.
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PMID:Transcripts of MYB-like genes respond to phosphorous and nitrogen deprivation in Arabidopsis. 1559 50

Seeds of pea (Pisum sativum L.) were germinated for four days over two sheets of filter paper moistened with H2O (control) and 5 mM Cd(NO3)2 or CuSO4 (treated). The relationship between heavy-metal stress and breakdown of storage compounds was studied. Germination rate and growth of radicle decreased, while the water content in stressed seeds remained around the control values. Cotyledons changed their biochemical constituents: disorders in the contents of micronutrients (Fe, Mn, Zn), free amino acids and soluble sugars were found. Decline of alpha-amylase activity as well as acid phosphatase were also observed, whereas beta-amylase and alkaline phosphatase ones were not modified by heavy-metal treatments. These results suggest that the inhibition of seed germinations after exposure to cadmium or copper is not the consequence of starvation in water uptake by seed tissues, but may be due to a failure in the reserve mobilization process from cotyledons.
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PMID:[Biochemical changes associated with cadmium and copper stress in germinating pea seeds (Pisum sativum L.)]. 1571 78

A Gram-negative, motile, rod-shaped bacterium, designated strain P1(T), was isolated from activated sludge of a municipal wastewater treatment plant. Phylogenetic analysis of its 16S rRNA gene sequence placed the novel isolate among representatives of the family Comamonadaceae. The closest relatives in reconstructed phylogenetic trees were Pseudomonas spinosa, Macromonas bipunctata and Hydrogenophaga species. Strain P1(T) was not able to grow anaerobically or autotrophically, reduced nitrate to nitrite and required vitamins for growth. Ubiquinone 8 (Q8) and 3-hydroxy-substituted fatty acids were present, but 2-hydroxy fatty acids were absent. The G+C content of the DNA was 67 mol%. Phenotypic characteristics allowed a clear differentiation of strain P1(T) from representatives of the genera Hydrogenophaga and Macromonas, whereas DNA-DNA hybridization experiments revealed that strain P1(T) did not belong to the species P. spinosa. As a peculiarity, cells of strain P1(T) and P. spinosa ATCC 14606(T) were able to accumulate large amounts of polyhydroxyalkanoates and polyphosphate in the form of large intracellular granules. Apparently in both strains nitrogen limitation stimulates the production of polyhydroxyalkanoates, whereas carbon starvation induces the formation of polyphosphates. Based upon phylogenetic and phenotypic evidence, it is proposed to establish the novel taxon Malikia granosa gen. nov., sp. nov., represented by the type strain P1(T) (=DSM 15619(T)=JCM 12706(T)=CIP 108194(T)). The most closely related species of strain P1(T) was P. spinosa. This species has been misclassified, and it is proposed to transfer it to the new genus Malikia as Malikia spinosa gen. nov., comb. nov. The type strain is ATCC 14606(T) (=DSM 15801(T)).
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PMID:Malikia granosa gen. nov., sp. nov., a novel polyhydroxyalkanoate- and polyphosphate-accumulating bacterium isolated from activated sludge, and reclassification of Pseudomonas spinosa as Malikia spinosa comb. nov. 1577 34


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