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

The mechanism by which cells recognize starvation to allow subsequent cellular development was analyzed using Dictyostelium discoideum, with special emphasis on Ca2+ as a crucial signal transducer in intra- and intercellular communications. As was expected, the cytosolic Ca2+ concentration ([Ca2+]i) in aequorin-expressing cells (RHI76 derived from D. discoideum Ax-3) was temporarily increased, when 3-5 microM thapsigargin (Tg), a specific inhibitor of the Ca(2+)-ATPase, was added into the cells incubated in semistarvation medium (SS-medium: 1 vol of growth medium plus 7 vol either of 20 mM Na2/K-phosphate buffer (pH 6.2) or of Bonner's salt solution (BSS)). Essentially the same result was obtained by the application of 5 microM nigericin (Ng), an acid ionophore to cells under the semistarved condition. Here it is of interest to note that in the SS-medium Tg and Ng are capable of enhancing cell differentiation as exemplified well by the earlier acquisition of chemotactic response to cAMP, possibly inducing the starvation response through the [Ca2+]i increase. From Western blot analysis of phosphotyrosine (pTyr)-containing proteins using anti-pTyr antibody, it was found that the pTyr-phosphorylation levels of 97-, 80-, and 45-kDa proteins increase specifically in response to starvation. Interestingly, Tg and Ng induced such a change of the 80-kDa protein in the cells incubated in the SS-medium. Taken together these results strongly suggest that the temporal increase of [Ca2+]i may be a matter of importance for signal transduction coupled with starvation response.
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PMID:The signals for starvation response are transduced through elevated [Ca2+]i in Dictyostelium cells. 959 7

Dictyostelium mutants expressing aequorin were used to study and compare the roles of heterotrimeric G-proteins and the second messengers IP3 and cGMP in regulating folate- and cAMP receptor-activated [Ca2+]i signals. The calcium responses of vegetative cells to folate were dramatically impaired in Gbeta and Galpha4 null mutants but were restored with altered kinetics and temperature-sensitivity in Gbeta null mutants overexpressing wild type and temperature-sensitive Gbeta isoforms. Folic acid receptors thus mediate changes in [Ca2+]i via a Galpha4betagamma-dependent pathway. Neither folate nor cAMP-induced [Ca2+]i signals were significantly altered in PLC null transformants, but [Ca2+]i changes elicited by both attractants were significantly prolonged in two stmF mutants lacking cGMP-specific phosphodiesterase activity. This confirms an important role of cGMP in regulating receptor-activated Ca2+ uptake and/or extrusion systems. This cGMP-dependent part of the Ca2+ response to cAMP stimuli was developmentally down-regulated and all but disappeared by the time the cells reached full aggregation competence after 8 h of starvation. The results suggest that folate and cAMP receptor-activated [Ca2+]i signals are regulated in a complex manner via multiple signalling pathways, one that is G-protein- and cGMP-dependent (present at the vegetative and early poststarvation stage) and another that is G-protein-independent (dominant in fully aggregation-competent cells at approximately 8 h poststarvation).
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PMID:Multiple signalling pathways connect chemoattractant receptors and calcium channels in Dictyostelium. 1295 83

The impact of calcium signals in virtually all cells has led to the study of their role in prokaryotic organisms as stress response modulators. Cell differentiation in adverse conditions is a common Ca(2+)-requiring response. Nitrogen starvation induces the differentiation of N(2)-fixing heterocysts in the filamentous cyanobacterium Anabaena sp. PCC7120. This paper reports the use of a recombinant strain of this organism expressing the photoprotein aequorin to monitor the intracellular free-calcium concentration during the course of heterocyst differentiation. A specific calcium signature that is triggered exclusively when cells are deprived of combined nitrogen and generated by intracellular calcium stores was identified. The intracellular calcium signal was manipulated by treatment with specific calcium drugs, and the effect of such manipulation on the process of heterocyst differentiation was subsequently assessed. Suppression, magnification or poor regulation of this signal prevented the process of heterocyst differentiation, thereby suggesting that a calcium signal with a defined set of kinetic parameters may be required for differentiation. A hetR mutant of Anabaena sp. PCC7120 that cannot differentiate into heterocysts retains, however, the capacity to generate the calcium transient in response to nitrogen deprivation, strongly suggesting that Ca(2+) may be involved in a very early step of the differentiation process.
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PMID:A calcium signal is involved in heterocyst differentiation in the cyanobacterium Anabaena sp. PCC7120. 1552 59

Using Ca2+-dependent photoprotein aequorin-transformed tobacco BY-2 cell suspensions, the sugar-induced increase in cytosolic free Ca2+ concentration ([Ca2+]cyt) was investigated by measuring the luminescence intensity. When 0.5 M sucrose or some other sugars were fed to the cells, strong and transient luminescence was observed. Salts or sugar analogues didn't show this effect. In addition, the intensity of sucrose-induced aequorin luminescence was gradually enhanced when cells were exposed to sugar-starvation. This was observed with the concurrent expression of the sucrose/H+ co-transporter, NtSUT1A. The [Ca2+]cyt increase may initiate Ca2+-signaling leading to the expression of genes related to biosynthesis of storage carbohydrates in a sink organ. The sugar-signaling may play an important role in the conversion on nutritional stage of plant tissue, source organ to sink organ.
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PMID:H+-Coupled sugar transporter, an initiator of sugar-induced Ca2+-signaling in plant cells. 1632 Jun 20

Phosphate (Pi) deficiency strongly limits plant growth, and plant roots foraging the soil for nutrients need to adapt to optimize Pi uptake. Ca2+ is known to signal in root development and adaptation but has to be tightly controlled, as it is highly toxic to Pi metabolism. Under Pi starvation and the resulting decreased cellular Pi pool, the use of cytosolic free Ca2+ ([Ca2+]cyt) as a signal transducer may therefore have to be altered. Employing aequorin-expressing Arabidopsis (Arabidopsis thaliana), we show that Pi starvation, but not nitrogen starvation, strongly dampens the [Ca2+]cyt increases evoked by mechanical, salt, osmotic, and oxidative stress as well as by extracellular nucleotides. The altered root [Ca2+]cyt response to extracellular ATP manifests during seedling development under chronic Pi deprivation but can be reversed by Pi resupply. Employing ratiometric imaging, we delineate that Pi-starved roots have a normal response to extracellular ATP at the apex but show a strongly dampened [Ca2+]cyt response in distal parts of the root tip, correlating with high reactive oxygen species levels induced by Pi starvation. Excluding iron, as well as Pi, rescues this altered [Ca2+]cyt response and restores reactive oxygen species levels to those seen under nutrient-replete conditions. These results indicate that, while Pi availability does not seem to be signaled through [Ca2+]cyt, Pi starvation strongly affects stress-induced [Ca2+]cyt signatures. These data reveal how plants can integrate nutritional and environmental cues, adding another layer of complexity to the use of Ca2+ as a signal transducer.
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PMID:Phosphate Starvation Alters Abiotic-Stress-Induced Cytosolic Free Calcium Increases in Roots. 3069 50

The root tip responds to mechanical stimulation with a transient increase in cytosolic free calcium as a possible second messenger. Although the root tip will grow through a heterogeneous soil nutrient supply, little is known of the consequence of nutrient deprivation for such signalling. Here, the effect of inorganic phosphate deprivation on the root's mechano-stimulated cytosolic free calcium increase is investigated. Arabidopsisthaliana (cytosolically expressing aequorin as a bioluminescent free calcium reporter) is grown in zero or full phosphate conditions, then roots or root tips are mechanically stimulated. Plants also are grown vertically on a solid medium so their root skewing angle (deviation from vertical) can be determined as an output of mechanical stimulation. Phosphate starvation results in significantly impaired cytosolic free calcium elevation in both root tips and whole excised roots. Phosphate-starved roots sustain a significantly lower root skewing angle than phosphate-replete roots. These results suggest that phosphate starvation causes a dampening of the root mechano-signalling system that could have consequences for growth in hardened, compacted soils.
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PMID:Phosphate Deprivation Can Impair Mechano-Stimulated Cytosolic Free Calcium Elevation in Arabidopsis Roots. 3294 34