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191.
Magnesium transport and function in plants: the tip of the iceberg 总被引:19,自引:0,他引:19
Orit Shaul 《Biometals》2002,15(3):307-321
The maintenance of Mg2+ homeostasis in the plant is essential for viability. This review describes Mg2+ functions and balancing in plants, with special focus on the existing knowledge of the involved transport mechanisms. Mg2+ is essential for the function of many cellular enzymes and for the aggregation of ribosomes. Mg2+ concentrations also modulate ionic currents across the chloroplast and the vacuolar membranes, and might thus regulate ion balance in the cell and stomatal opening. The significance of Mg2+ homeostasis has been particularly established with regard to Mg2+'s role in photosynthesis. Mg2+ is the central atom of the chlorophyll molecule, and fluctuations in its levels in the chloroplast regulate the activity of key photosynthetic enzymes. Relatively little is known of the proteins mediating Mg2+ uptake and transport in plants. The plant vacuole seem to play a key role in Mg2+ homeostasis in plant cells. Physiological and molecular evidence indicate that Mg2+ entry to the vacuole is mediated by Mg2+/H+ exchangers. The Arabidopsis vacuolar Mg2+/H+ exchanger, AtMHX, is highly transcribed at the vascular tissue, apparently most abundantly at the xylem parenchyma. Inclusion of Mg2+ ions into the vacuoles of this tissue may determine their partitioning between the various plant organs. Impacts of Mg2+ imbalance are described with respect for both plant physiology and for its nutritional value to animal and human. 相似文献
192.
Tragedy of the commons as a result of root competition 总被引:23,自引:2,他引:21
193.
De Dreu CK Greer LL Handgraaf MJ Shalvi S Van Kleef GA 《Proceedings. Biological sciences / The Royal Society》2012,279(1731):1150-1154
In intergroup competition and conflict, humans benefit from coalitions with strong partners who help them to protect their in-group and prevail over competing out-groups. Here, we link oxytocin, a neuropeptide produced in the hypothalamus, to ally selection in intergroup competition. In a double-blind placebo-controlled experiment, males self-administered oxytocin or placebo, and made selection decisions about six high-threat and six low-threat targets as potential allies in intergroup competition. Males given oxytocin rather than placebo viewed high-threat targets as more useful allies and more frequently selected them into their team than low-threat targets. 相似文献
194.
Adam Izdebski Lee Mordechai Sam White 《Human ecology: an interdisciplinary journal》2018,46(3):291-303
We examine the social burden associated with resilience to environmental shocks in pre-modern societies. We argue that analyses of state-level interventions to mitigate the consequences of catastrophic events tend to isolate these measures from their larger social contexts and thereby overlook the uneven distribution of their burden across different groups. We use three cases of pre-modern societies in the northeastern Mediterranean - the sixth century Roman Empire, the tenth century Byzantine Empire, and the sixteenth century Ottoman Empire. We demonstrate how the adaptive processes that reinforced resilience at the state level incurred different burdens for those at lower levels of the social hierarchy. We found that some groups sustained losses while others gained unexpected benefits in the context of temporary systemic instability. We also found that although elites enjoyed enhanced buffers against the adverse effects in comparison with non-elites, this did not consistently guarantee them a better outcome. We conclude that the differentiated burden of resilience could in some cases entrench existing political or economic configurations, and in other cases, overturn them. Our case studies indirectly address the pressing issue of environmental justice. 相似文献
195.
196.
Hagai Karchi Orit Shaul Gad Galili 《The Plant journal : for cell and molecular biology》1993,3(5):721-727
In order to study the regulation of threonine and methionine synthesis in plant seeds, tobacco plants were transformed with a chimeric gene containing the coding DNA sequence of a mutant lysC gene from Escherichia coli fused to a promoter from a phaseolin seed storage protein gene. The bacterial mutant lysC gene codes for aspartate kinase (AK) which is desensitized to feedback inhibition by lysine and threonine. Increased AK activity, compared with control non-transformed plants, was detected in seeds but not in leaves, roots and flowers of the transgenic plants. This expression was accompanied by a significant increase in the levels of free threonine and methionine in the seed. The level of these amino acids also correlated positively with the levels of the bacterial enzyme. No alteration in plant phenotype and 'average seed weight' was observed in any of the transgenic plants, indicating that plant growth and seed development were normal. This study demonstrates, for the first time, that the threonine and methionine biosynthetic pathways are active in plant seeds. Thus, targeting of the production of favorable biosynthetic enzymes to plant seeds may represent a desirable molecular approach for production of crop plants with a more balanced nutritional quality. 相似文献
197.
Ilan G. Ron Moshe J. Inbar Mordechai Gutman Ofer Merimsky Samario Chaitchik 《Cancer immunology, immunotherapy : CII》1993,37(1):61-66
Thirty-four evaluable patients with metastatic malignant melanoma were entered into a phase-II study designed to assess the response rate and analyze the long-term therapeutic efficacy of recombinant interferon (rIFN) -2a and dacarbazine. Patients received 14 days of daily subcutaneous r-IFN-2a (3×106 IU/day), followed by 9×106 IU on alternate days, as long as objective response lasted, in combination with i.v. dacarbazine started on day 7 (400 mg/m2) and repeated every 21 days (dacarbazine doses were escalated to 800 mg/m2). In 11 patients, 6 complete (17.6%) and 5 partial (14.7%) responses were seen, with an overall response rate of 32.3% (95% confidence interval: 16%–48%). The median survival time of the responding patients was significantly better than that of patients with progressive disease (P=0.01) and the median response time of the patients showing complete response was longer than that of the partially responding patients (14 and 7 months respectively,P=0.06). 相似文献
198.
Preciado-Patt Liana Cahalon Liora Hershkovitz Rami Lider Ofer Pras Mordechai Fridkin Mati 《International journal of peptide research and therapeutics》1998,5(5-6):349-355
Summary Serum amyloid A (SAA), an acute-phase reactant, exists naturally as a minor protein in the sera of healthy individuals. However,
its levels in sera are increased markedly during various transient and chronic inflammatory diseases, often concomitantly
with accumulation at inflicted sites. SAA is synthesized mainly in the liver following the synergistic action of cytokines,
mainly tumor necrosis factor-α (TNF-α) and interleukin-1 and-6 (IL-1 and IL-6). It was already shown by us that upon interaction
with SAA or amyloid A (AA), the extracellular matrix (ECM) and laminin induced the adhesion of resting human CD4+ T-cells in an apparently β1-integrin-mediated manner. Herein we have shown that the SAA-ECM complex modulates the regulation of cytokine synthesis by
human T-lymphocytes. The SAA-ECM complex dramatically enhanced the release of TNF-α by human T-cells in a dose-dependent manner,
reaching its maximal effect in the presence of 100 μM recombinant SAA. The SAA domain, responsible for the enhanced release
of TNF-α by human T-lymphocytes, is apparently the amyloid A protein (AA, i.e. SAA2-82). Specifically, TNF-α enhanced secretion
is mediated through intimate interactions of SAA/AA, with laminin. Thus, the ECM serving as a temporary anchorage site for
SAA and AA seems to be involved in regulating TNF-α secretion and the recruitment and accumulation of immunocytes in extravascular,
inflammatory compartments. 相似文献
199.
Nuclear accumulation of fibroblast growth factor receptors is regulated by multiple signals in adrenal medullary cells. 总被引:10,自引:3,他引:7 下载免费PDF全文
M K Stachowiak P A Maher A Joy E Mordechai E K Stachowiak 《Molecular biology of the cell》1996,7(8):1299-1317
In an effort to determine the localization of fibroblast growth factor (FGF) receptors (FGFR) that could mediate the intracellular action of FGF-2, we discovered the presence of high-affinity. FGF-2 binding sites in the nuclei of bovine adrenal medullary cells (BAMC). Western blot analysis demonstrated the presence of 103-, 118-, and 145-kDa forms of FGFR1 in nuclei isolated from BAMC. 125I-FGF-2 cross-linking to nuclear extracts followed by FGFR1 immunoprecipitation showed that FGFR1 can account for the nuclear FGF-2 binding sites. Nuclear FGFR1 has kinase activity and undergoes autophosphorylation. Immunocytochemistry with the use of confocal and electron microscopes demonstrated the presence of FGFR1 within the nuclear interior. Nuclear subfractionation followed by Western blot or immunoelectron microscopic analysis showed that the nuclear FGFR1 is contained in the nuclear matrix and the nucleoplasm. Agents that induce translocation of endogenous FGF-2 to the nucleus (forskolin, carbachol, or angiotensin II) increased the intranuclear accumulation of FGFR1. This accumulation was accompanied by an overall increase in FGF-2-inducible tyrosine kinase activity. Our findings suggest a novel mode for growth factor action whereby growth factor receptors translocate to the nucleus in parallel with their ligand and act as direct mediators of nuclear responses to cell stimulation. 相似文献
200.
Mazal Shimon Yakov Egozi Yoel Kloog Mordechai Sokolovsky Sasson Cohen 《Journal of neurochemistry》1989,53(2):561-565
The two parameters of the active [methyl-3H]choline uptake into isolated rat forebrain microvessels, Km and Vmax, were determined for 1-, 3-, 10-, and 24-month-old Charles River male rats and compared with the activities of the enzymes choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) in these microvessels over the same time course. The value of Km remained constant over the entire period, but that of Vmax increased from 8.5 +/- 1.0 to 80.6 +/- 16.4 nmol g-1 (mean +/- SEM) over the first 3 months of life. Over the same period, the increase in ChAT activity, from an initial value of 7.1 +/- 1.6 to 10.2 +/- 0.3 nmol g-1 min-1, was not proportional to that of choline uptake. Levels of BuChE activity (0.9-1.3 mumol g-1 min-1) were almost unchanged throughout the entire 24-month period, but those of AChE showed a steady and significant increase from 1 to 24 months, remaining relatively high at senescence (4.7 mumol g-1 min-1), when choline uptake had decreased to one-third of its optimal value. Selective inhibition of AChE with 1,5-bis(4-allyldimethylammonium-phenyl)pentan-3-one dibromide (0.5 microM) in unruptured capillaries from 3-month-old rats resulted in a decrease in Vmax of choline uptake from approximately 81 to 59 nmol g-1 min-1 or with 9-amino-1,2,3,4-tetrahydroacridine (10 microM) in capillaries from 2-month-old rats from approximately 30 to 15 nmol g-1 min-1. Selective inhibition of BuChE with tetraisopropyl pyrophosphoramide (100 microM) resulted in an increase in Vmax from approximately 81 to 96 nmol g-1 min-1. It is possible that the two vascular enzyme systems are coupled to a hypothetical endothelial choline transporter, but with an action opposite to each other. 相似文献