1,721,173 research outputs found
Phosphorylation-dephosphorylation of membrane proteins controls the microsomal H+-ATPase activity of corn roots
No full textThe Mg2+-dependent H+-ATPase activity of a sealed microsomal vesicle fraction isolated from corn (Zea mays L.) roots appears to be controlled by a phosphorylation-dephosphorylation cycle. Phosphorylation of the microsomal fraction is carried out by a Ca2+/calmodulin (CaM)-stimulated process. The H+-ATPase activity decreases with increasing phosphorylation of the membranes and becomes only slightly uncoupled by ionophores and less inhibited by dicyclohexylcarbodiimide (DCCD), diethylstilbestrol (DES), NO3− and vanadate. The inhibitory effect of phosphorylation is greater on the NO3−-sensitive H+-ATPase activity than on the vanadate-sensitive activity. Restoration of H+-ATPase activity is achieved by allowing the phosphorylated membranes to dephosphorylate either in the absence or presence of exogenous alkaline phosphatase. Moreover, the presence of fluphenazine during the Ca2+/CaM-stimulated treatment inhibits membrane phosphorylation and protects the H+-ATPase activity from inhibition
ATPases and other enzymatic activities in potato tubers during storage at different temperatures
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Effect of Fe deficiency on mitochondrial alternative NAD(P)H dehydrogenases in cucumber roots
No full textIron deficiency affects the function of respiratory chain, mainly at the complex I and complex II levels. Since plant mitochondria posses alternative NAD(P)H dehydrogenases located in the inner-membrane, oxidising NAD(P)H from both cytosol and matrix, we investigated these activities in mitochondria of Fe-deficient roots. External and internal NAD(P)H dehydrogenase activities increased in Fe-deficient mitochondria. Accordingly, NDB1 protein strongly accumulates while NDA1 does not show relevant differences in Fe-deficient roots. The data presented support, for the first time, the hypothesis that Fe deficiency induces the alternative NAD(P)H dehydrogenases bypassing the impaired complex I
Calcium physiology and metabolism in fruit trees
No full textCalcium plays an important role in plant growth and development. Its importance as a mineral nutrient has two main purposes: apoplastic and symplastic. Apoplastic calcium has an important structural and functional role in the plant cell walls and membranes. Cell wall is reach in pectinaceous materials that contribute to cell cohesiveness and is believed to constitute an important site of calcium interaction. Integrity of the membranes is important for maintaining its selectivity. In these cases a millimolar calcium concentration is necessary in order to fulfil its requirements as cementing material and as source of calcium readily accessible to membrane surface and subsequently to internal compartments. The symplastic concentration of calcium has to be maintained at the micromolar level to serve as an intracellular "second messenger". This is maintained through the action of different transport mechanisms localised on the membranes which extrude the ion from the cytosol towards the cell wall or other intracellular organelles. Transient increase in cytosolic calcium is the way to activate metabolic reactions in response to extra- or intracellular signals. Calcium alone or its complex with calmodulin activates protein kinases that through covalent modification of other target enzymes will modulate the physiological responses
Plasma membrane-bound H+-ATPase and reductase activities in Fe-deficient cucumber roots
No full textPhysiological and biochemical modifications induced by Fe-deficiency have been studied in cucumber (Cucumis sativus L. cv. Marketer) roots, a Strategy I plant that initiates a rapid acidification of the medium and an increase in the electric potential difference when grown under Fe-deficiency. Using the aqueous two-phase partitioning method, a membrane fraction which has the plasmalemma characteristics was purified from roots of plants grown in the absence and in the presence of iron. The plasma membrane vesicles prepared from Fe-deficient plants showed an H+-ATPase activity (EC 3.6.1.35) that is twice that of the non-deficient control. Furthermore, membranes from Fe-deficient plants showed a higher capacity to reduce Fe3+-chelates. The difference observed in the reductase activity was small with ferricyanide (only 30%) but was much greater with Fe3-EDTA and Fe3-citrate (210 and 250%, respectively). NADH was the preferred electron donor for the reduction of Fe3+ compounds. Fe3+ reduction in plasma membrane from cucumber roots seems to occur with utilisation of superoxide anion, since addition of superoxide dismutase (SOD; EC 1.15.1.1) “in vitro” decreased Fe3+ reduction by 60%.
The response and the difference induced by iron starvation on these two plasma membrane activities together with a possible involvement of O2 in controlling the Fe3+/Fe2+ ratio in the rhizosphere are discussed
Studio degli effetti della carenza di ferro sull’attività fotorespiratoria
No full textIl Ferro (Fe) è un elemento essenziale per tutti gli organismi viventi come cofattore di vari processi biochimici quali fotosintesi, respirazione, sintesi del DNA. L'effetto più evidente della Fe-carenza nelle piante è una marcata clorosi causata dalla mancata sintesi di clorofilla, che può tradursi in limitazioni della fotosintesi e/o in fotoinibizione, nonché in una riduzione del tasso di assimilazione della CO2.
In queste condizioni, la generazione di specie reattive dell'O2 (ROS) può indurre stress ossidativo e danni al fotosistema II (PSII) e, a volte, al fotosistema I (PSI). La fotorespirazione può essere considerata come un ciclo operante tra cloroplasti, perossisomi, mitocondri e citosol, che contribuisce a proteggere le piante da fotoinibizione e accumulo eccessivo di ROS.
Nella parte iniziale del lavoro, piante di Cucumis sativus L. sono state allevate a diversa biodisponibilità di Fe nel tempo, per studiare l’eventuale relazione tra Fe-carenza e attività fotorespiratoria, mediante un approccio che prevede la caratterizzazione metabolica dei diversi comparti cellulari coinvolti. Analisi preliminari in vivo di parametri fotosintetici e di fluorescenza della clorofilla suggeriscono una reale limitazione della fotosintesi e una induzione delle vie alternative di dissipazione dell’eccesso di energia fotochimica.
Sono stati condotti saggi di attività di enzimi coinvolti nella fotorespirazione. I dati ottenuti mostrano una netta riduzione di attività degli enzimi Fe-dipendenti.
E' stata intrapresa la purificazione della frazione perossisomiale, allo scopo di condurre analisi Western Blot di enzimi del ciclo fotorespiratorio. I dati ottenuti, insieme a dati pregressi, suggeriscono che lo squilibrio nel macchinario fotosintetico indotto da Fe-carenza possa essere compensato da una maggiore attivazione della fotorespirazione. In seguito verrà condotta la purificazione di cloroplasti e di mitocondri e questi verranno caratterizzati in condizioni di Fe-carenza
The interplay between photorespiration and iron deficiency : a preliminary investigation
No full textIron (Fe) is an essential element for living organisms being a cofactor of many metabolic processes. The most noticeable effect of Fe deficiency in leaves is a marked chlorosis caused by a lack in chlorophyll biosynthesis which results in reduction of photosynthesis and induction of oxidative stress. Photorespiration can be considered as a cycle which helps to defend plants from those impairments.
Metabolic characterization of Cucumis sativus L. plants grown at different Fe concentration was performed to investigate the interplay among Fe deficiency and photorespiration. In vivo analysis of photosynthetic and chlorophyll fluorescence parameters suggest limitations in photosynthesis and induction of other energy dissipation processes. The activity of Fe-dependent enzymes involved in photorespiration was lower in Fe-deprived plants.
Purification of the peroxisomal fraction to carry out Western Blot analysis of enzymes belonging to photorespiration was undertaken. Our data suggest that the imbalance induced by Fe deficiency may be balanced by increased rate of photorespiration. Future perspective will be the purification and characterization of Fe-deficient chloroplasts and mitochondria
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