University of the Mediterranean

About: University of the Mediterranean is a based out in . It is known for research contribution in the topics: Population & HERA. The organization has 2466 authors who have published 2262 publications receiving 85298 citations. The organization is also known as: Université de la Mediterranée Aix-Marseille II & Aix-Marseille II.

The Finite Group Velocity of Quantum Spin Systems

Abstract: It is shown that if Ф is a finite range interaction of a quantum spin system, τ t Ф the associated group of time translations, τ x the group of space translations, and A, B local observables, then $$ \mathop {{\text{lim}}}\limits_{\mathop {\left| t \right| \to \infty }\limits_{\left| x \right| > v\left| t \right|} } \left\| {\left[ {\tau _t^\varphi \tau \left( A \right),B} \right]} \right\|e^{\mu \left( v \right)t} = 0$$ (1) whenever v is sufficiently large (ν > V Ф ,) where μ(ν) > 0. The physical content of the statement is that information can propagate in the system only with a finite group velocity.

Early steps of lymphocyte activation bypassed by synergy between calcium ionophores and phorbol ester

Abstract: Although it has been proposed that the activation of T lymphocytes is mediated by an early rise in cytosolic calcium concentration, it has not been possible to mimic antigen- or mitogen-induced mouse lymphocyte activation by calcium ionophores that bypass receptor-mediated processes. There is now evidence from other systems that the rise in cytosolic calcium which follows receptor triggering is preceded by the breakdown of phosphatidylinositol bisphosphate into 1,2-diacylglycerol and inositol trisphosphate. The latter is known to cause release of calcium from intracellular stores. The cellular target for the former is now widely accepted to be protein kinase C. Therefore, ligand-induced cellular response follows a rise in cytosolic calcium concentration and protein kinase C activation. Here we confirm that the calcium ionophores A23187 and ionomycin do not activate mouse T lymphocytes. However, either one in combination with the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), which is structurally related to 1,2-diacylglycerol, induces in lymphoid cell populations the expression of receptors for interleukin-2 (IL-2), the secretion of IL-2 and cell proliferation as measured by 3H-thymidine uptake. The growth-promoting effect of IL-2 on an exogenous IL-2-dependent clone could not be substituted for by ionomycin either alone or with TPA. Thus, the combination of calcium ionophores and TPA bypasses the requirement for antigen- or lectin-induced signal at the onset of lymphocyte activation.

State transitions and light adaptation require chloroplast thylakoid protein kinase STN7

Abstract: Photosynthetic organisms are able to adjust to changing light conditions through state transitions, a process that involves the redistribution of light excitation energy between photosystem II (PSII) and photosystem I (PSI). Balancing of the light absorption capacity of these two photosystems is achieved through the reversible association of the major antenna complex (LHCII) between PSII and PSI (ref. 3). Excess stimulation of PSII relative to PSI leads to the reduction of the plastoquinone pool and the activation of a kinase; the phosphorylation of LHCII; and the displacement of LHCII from PSII to PSI (state 2). Oxidation of the plastoquinone pool by excess stimulation of PSI reverses this process (state 1). The Chlamydomonas thylakoid-associated Ser-Thr kinase Stt7, which is required for state transitions, has an orthologue named STN7 in Arabidopsis. Here we show that loss of STN7 blocks state transitions and LHCII phosphorylation. In stn7 mutant plants the plastoquinone pool is more reduced and growth is impaired under changing light conditions, indicating that STN7, and probably state transitions, have an important role in response to environmental changes.