The effect of ions, ion channel blockers, and ionophores on uptake of vitellogenin into cockroach follicles

Since calcium plays an important role in vitellogenin binding and uptake in Nauphoeta cinerea and because calcium channels have been described in follicles of this species, we investigated the effect of various ions, ionophores, and ion channel blockers on vitellogenin uptake in vitro. Calcium significantly stimulated vitellogenin uptake; this effect could be substituted best by barium and less well by strontium and magnesium. The stimulatory effect of calcium, and to a certain extent also that of barium, was dependent on the vitellogenin concentration, whereas the effect of strontium and magnesium was not. In the presence of calcium, vitellogenin uptake was inhibited by barium, strontium, and magnesium as well as by the transition elements nickel, cobalt, and zinc, but not by manganese which had a stimulatory effect. Valinomycin, verapamil, tetraethylammonium, and atropine reduced vitellogenin uptake, while amiloride and ouabain were ineffective. Our results indicate that calcium inward (and possibly potassium outward) fluxes play an important role in vitellogenin uptake.     

Inhibition of active strontium transport from erythrocyte ghosts by internal calcium: Evidence for a specificity controlling site

Summary The inhibition of strontium transport from erythrocyte ghosts by internal calcium was investigated. When active strontium transport was measured in the presence of increasing levels of internal calcium it was found that the inhibition of strontium transport started at an internal calcium level of 0.3mm and was virtually complete when this concentration reached 1.0mm. It was also noted that calcium transport was virtually constant between concentrations of 0.3 and 1.0mm. This experiment indicated that calcium did not inhibit strontium transport by competing for the active site of the transport system. This inhibition was partially reversed by increasing the internal magnesium concentration from 1 to 4mm. A higher level of magnesium at the time of lysis and during incubation enhanced strontium transport. However, the inhibition remained noncompetitive with respect to calcium. Manganese was also found to support calcium and strontium transport. However, it could not reverse the inhibition of strontium transport by internal calcium at any concentration tested. In fact, manganese restored the inhibition of strontium transport by calcium in ghosts that were prepared and incubated in solutions that had high magnesium levels.     

Ionic Regulation of the Binding of dl-[3H]2-Amino-4-Phosphonobutyrate to l-Glutamate-Sensitive Sites on Rat Brain Membranes

Abstract: The effects of ions on the binding of the excitatory amino acid analogue dl -[³H]2-amino-4-phosphon-obutyrate to l -glutamate-sensitive sites on rat brain synaptic membranes was investigated. The divalent cations manganese, magnesium, strontium, and particularly calcium, produced a marked enhancement in specific binding. However, this effect was manifest only in the presence of added chloride, or to a lesser extent, with bromide ions. Application of saturation analysis revealed that both chloride and calcium acted to increase the binding site density in a concentration-dependent manner, without affecting the dissociation constant. The only other ionic species found to have a significant effect on 2-amino-4-phosphonobutyrate binding was sodium, which produced an apparent reduction in site affinity, without modifying the binding site density. Although the significance of these striking ionic effects is as yet unknown, it seems feasible that chloride (and possibly also calcium) ions may serve a role in regulating the interaction of excitatory amino acids with their physiological receptors.     

Presynaptic strontium dynamics and synaptic transmission

Strontium can replace calcium in triggering neurotransmitter release, although peak release is reduced and the duration of release is prolonged. Strontium has therefore become useful in probing release, but its mechanism of action is not well understood. Here we study the action of strontium at the granule cell to Purkinje cell synapse in mouse cerebellar slices. Presynaptic residual strontium levels were monitored with fluorescent indicators, which all responded to strontium (fura-2, calcium orange, fura-2FF, magnesium green, and mag-fura-5). When calcium was replaced by equimolar concentrations of strontium in the external bath, strontium and calcium both entered presynaptic terminals. Contaminating calcium was eliminated by including EGTA in the extracellular bath, or by loading parallel fibers with EGTA, enabling the actions of strontium to be studied in isolation. After a single stimulus, strontium reached higher peak free levels than did calcium (approximately 1.7 times greater), and decayed more slowly (half-decay time 189 ms for strontium and 32 ms for calcium). These differences in calcium and strontium dynamics are likely a consequence of greater strontium permeability through calcium channels, lower affinity of the endogenous buffer for strontium, and less efficient extrusion of strontium. Measurements of presynaptic divalent levels help to explain properties of release evoked by strontium. Parallel fiber synaptic currents triggered by strontium are smaller in amplitude and longer in duration than those triggered by calcium. In both calcium and strontium, release consists of two components, one more steeply dependent on divalent levels than the other. Strontium drives both components less effectively than does calcium, suggesting that the affinities of the sensors involved in both phases of release are lower for strontium than for calcium. Thus, the larger and slower strontium transients account for the prominent slow component of release triggered by strontium.     

Immune T lymphocyte to tumor cell adhesion. Magnesium sufficient, calcium insufficient

The prelytic adhesion of immune cytolytic thymus-derived lymphocytes to specific antigen-bearing ascites tumor target cells has been studied. A new assay was used in which adhesions are permitted to form for 2.5 min; the cells are then dispersed to prevent further adhesion, and the predispersion adhesions are quantitated by subsequent 51Cr release from the tumor cells as a result of cytolytic activity of the adhering lymphocytes. There were the following new findings: (a) magnesium is sufficient to support optimal adhesion formation even when EGTA is added to remove contaminating traces of calcium; (b) calcium supports no adhesion formation when traces of contaminating magnesium are removed by pretreating the medium with a chelating ion exchange resin; (c) calcium synergizes with suboptimal magnesium, increasing the apparent adhesion-supporting potency of magnesium 20-fold in the presence of 50 microM calcium; (d) in the presence of optimal magnesium (2--4 mM), calcium has not effect on the properties of the adhesion by any of six criteria; and (e) manganese supports adhesion better than magnesium, and strontium is ineffective. A survey of previous literature indicates that these results are remarkably similar to the predominant pattern for nonimmunologic cell adhesion (e.g., fibroblasts) involving cells from a variety of tissues in late embryonic and adult avians and mammals. This suggests that a "magnesium sufficient, calcium insufficient" mechanism may be found among the latter types of cell adhesions when appropriately examined. Moreover, it seems that the present lymphocyte-tumor cell adhesion, although evoked by specific receptor-antigen recognition, relies predominantly on mechanisms common to nonimmunologic intercellular adhesion processes.     

CALCIUM-BINDING PHOSPHOPROTEIN OF PIG BRAIN: EFFECTS OF CATIONS ON THE CALCIUM BINDING

—The effects of various cations on the calcium-binding properties of a brain phosphoprotein have been investigated employing an ultrafiltration binding assay. Sodium, magnesium, barium, strontium and manganese ions were competitive inhibitors of the calcium binding, and their affinity for the calcium-binding site increased in the order given. Potassium was a non-competitive inhibitor. Lanthanum, lead, mercuric and cadmium ions precipitated the phosphoprotein from solution. These findings are discussed in relation to a postulated role for the protein as a calcium-receptor molecule involved in release of neurotransmitters.     

The action of strontium on basophil leukocytes and its use to probe the relationship between immunologic stimulus and secretory response.

Strontium will substitute for calcium in the activation of histamine secretion from human basophil leukocytes stimulated by an immunologic reaction or by the ionophore A23187. Strontium is required in 10-fold higher concentration (1 to 10 mM) to activate histamine release compared with calcium (0.1 to 1.0 mM). In terms of maximum release obtainable for a particular immunologic stimulus, strontium is more effective than calcium. Results are presented to show that calcium and strontium act at the same site but strontium is a more sensitive probe for that site. Strontium can be used to demonstrate that immunologic stimuli activate calcium-binding sites in basophils even when no secretion is observed in the presence of calcium. It is suggested that the degree of secretion observed from basophils depends on the number of occupied Fc receptors for IgE and the coupling of these Fc receptors to calcium transport sites.     

Factors in the inactivation of postjunctional membrane receptors of frog skeletal muscle

Several factors which influence the rate of inactivation of muscle postjunctional membrane (PJM) receptors during the sustained application of carbamylcholine (CARB) have been studied by two methods. The rate of inactivation was increased by elevating the tonicity of the bathing medium, by increasing the CARB concentration, by raising the calcium ion concentration, and by substituting SO₄ ⁼ for Cl^- ions in the extracellular fluid. The relative effectiveness of calcium and other divalent cations in receptor inactivation was compared. In the absence of calcium, other divalent cations such as magnesium, strontium, or manganese were not efficient substitutes for calcium. In the presence of calcium, the addition of strontium or manganese ions accelerated the rate of receptor inactivation, but the addition of magnesium (up to 12 mM) inhibited this process. The inactivation of the membrane receptors in denervated muscle fibers was found to be similar to that in innervated muscle fibers. Various factors in PJM receptor inactivation are discussed. It is suggested that PJM receptor inactivation is influenced by the binding of calcium ions to sites on the internal surface of the PJM.     

An increase of late sodium current induces delayed afterdepolarizations and sustained triggered activity in atrial myocytes

This study determined the role of a slowly inactivating component of sodium current (I(Na)), late I(Na), to induce delayed afterdepolarizations (DADs) and triggered activity. We hypothesized that an increase of late I(Na) may induce not only early afterdepolarizations (EADs), but also intracellular calcium overload and DADs. Guinea pig atrial myocytes were studied using the whole cell patch-clamp technique. Anemone toxin II (ATX-II) (5-10 nmol/l) was used to enhance late I(Na). Ranolazine (10 micromol/l) and TTX (2 micromol/l) were applied to block ATX-II-induced late I(Na). ATX-II prolonged action potential duration and induced EADs. In the continuous presence of ATX-II, following the appearance of EADs, both DADs and sustained triggered activity occurred. Triggered activity was abolished and DADs were reduced by either ranolazine or TTX. Consistent with induction of DADs, ATX-II induced the transient inward current (I(TI)). The amplitude of I(TI) was significantly reduced by ranolazine. ATX-II induced only EADs, but no DADs, in the presence of the sodium-calcium exchange inhibitor KB-R7943 or the sarcoplasmic reticulum calcium release channel inhibitor ryanodine, or when the calcium chelator EGTA or BAPTA was included in the pipette solution. In conclusion, an increase of late I(Na), in addition to inducing EADs, can cause cellular calcium overload and induce DADs and sustained triggered activity in atrial myocytes. The data reveal that an increase of late I(Na) is a novel mechanism for initiation of atrial arrhythmic activity.     

Recycling of Synaptic Vesicles at the Frog Neuromuscular Junction in the Presence of Strontium

Abstract: In these experiments, we followed the exocytosis and endocytosis of synaptic vesicles with the vital dye FM1-43 and asked whether calcium is important for membrane retrieval at the frog neuromuscular junction. We replaced calcium with equimolar amounts of strontium and monitored the staining of recycling vesicles by inducing exocytosis with electrical stimulation. Trains of 2,400 (2 or 20 Hz) or 4,200 (20 Hz) pulses failed to induce FM1-43 internalization in the presence of strontium, but they did in the presence of calcium. This effect of strontium was not due to a decrease in exocytosis, because FM1-43 release was similar in the presence of calcium or strontium. The impairment in endocytosis, observed as inhibition of FM1-43 internalization, could be overcome by longer periods of stimulation (6,000 pulses at 2 or 20 Hz) in the presence of strontium (1.8 m M ) or by increasing the extracellular concentration of strontium to 10 m M (2,400 action potentials at 20 Hz). It is suggested that endocytosis is dependent on calcium influx and that strontium is much less effective in replacing calcium for endocytosis than it is for exocytosis.     

Eimeria tenella: Incomplete Excystation in the Presence of EDTA in a Taurodeoxycholate-Based Medium

ABSTRACT. Normally, sporozoites of Eimeria tenella are efficiently excysted in vitro with trypsin and bile salts. However, a one hour treatment at °40C with a chelator-supplemented excystation medium (purified trypsin and chymotrypsin, taurodeoxycholate and ethylenediaminetetraacetic acid in buffered saline) produced incomplete excystation. The treatment removed the sporocyst plug and left an opened sporocyst containing motile sporozoites, but the release of sporozoites was greatly reduced (<12% release). Some of the sporozoites extended a portion of their anterior end through the sporocyst opening then retracted it into the sporocyst. Sporozoites were released when magnesium was added to the chelator-supplemented medium. Manganese was less effective and calcium was ineffective in producing release. Also, sporozoites were released when the incompletely excysted sporocysts were transferred to buffered saline with albumin and this became the basis for a new assay. The assay demonstrated that ethylenediaminetetraacetic acid reduced release in the presence of taurodeoxycholate but not in its absence. Hydrophobic and hydrophilic chelators were tested in the assay. Ethylene-dioxy diethylene-dinitrilotetraacetic acid and 8-hydroxyquinoline were inactive. The chelator 1,10-phenanthroline did not require bile salt to reduce release. The inhibitory effects by phenanthroline were eliminated in the presence of magnesium or manganese, while calcium had no effect. Thus, although certain chelators can inhibit release, a consistent correlation between chelation and inhibition of release has not been established. The application of ethylenediaminetetraacetic acid with taurodeoxycholate as a reversible inhibitor of release is discussed.     

ON THE RELATIONSHIP BETWEEN [3H]CHOLINE UPTAKE ACTIVATION AND [3H]ACETYLCHOLINE RELEASE

The depolarization-induced, calcium-dependent release of [³H]ACh from hippocampal synaptosomes was studied in a superfusion system. Release increased, with increasing depolarization. Barium and strontium effectively substituted for calcium during the depolarization, but magnesium inhibited the release. Releasable [³H]ACh is derived from the sodium-dependent component of the [³H]choline uptake which points out the physiologic importance of sodium-dependent choline transport. It is concluded that [³H]ACh release in this system has the same properties as neurotransmitter release in many other systems. Previous studies have shown that treatments which alter the activity of cholinergic neurons in vivo result in parallel changes in sodium-dependent choline uptake in vitro. When synaptosomes were utilized from animals treated to reduce cholinergic activity, there was a reduced release following the reduced uptake. Conversely, when synaptosomes were taken from animals treated to increase sodium-dependent choline uptake, there was an increase in the release. It is concluded that the changes in sodium-dependent choline uptake in vitro consequent to changes in neuronal activity in vivo result in parallel changes in releasable ACh. A comparison was made between the effect of a number of ions and agents on release and their effect on the in vitro, depolarization-induced activation of sodium-dependent choline uptake. Barium and strontium, ions which substitute for calcium in the release process, support the in vitro activation of uptake. Vinblastine and Bay a 1040, compounds which block release, prevented the in vitro activation of sodium-dependent choline uptake. However, magnesium blocked release in a dose-dependent manner, but did not block the activation of uptake in vitro. Rather, magnesium substituted for calcium and supported the activation of uptake in a dose-dependent fashion. It is concluded that acetylcholine release is not necessary for the activation of choline uptake.     

Effect of divalent cations of the amphetamine-induced stimulation of [3H]catechol synthesis in the striatum.

Abstract— The effects of divalent cations on the stimulation of [³H]catechol formation in striatal slices induced by d-amphetamine was studied in order to determine the role of calcium in this action of amphetamine. In the absence of any divalent cations in the medium, amphetamine did not significantly stimulate [³H]catechol synthesis in striatal slices, but it produced a marked stimulation of synthesis when calcium (1.25 mm ) was added to the medium. In the presence of calcium (1.25 mm ), high concentrations of magnesium (15mm ), other divalent cations (2.5 mm ) such as barium, strontium, manganese and cobalt, as well as verapamil, inhibited the amphetamine-induced stimulation. When the slices were incubated in medium containing no divalent cations, the addition to the medium of either strontium, cobalt, zinc, or magnesium (2.5 mm ) could not support the amphetamine-induced stimulation of [³H]catechol synthesis, while the addition of barium resulted in a significant stimulation of synthesis. In contrast, the stimulation produced by amphetamine in the presence of manganese was comparable to that observed when calcium had been added to the medium. Since amphetamine did not alter the specific activity of [³H]tyrosine in the tissue in the presence of any of the divalent cations tested, the amphetamine-induced stimulation of [³H]catechol synthesis was probably due to an increase in tyrosine hydroxylase activity. Calcium and manganese were also able to support the stimulation of [³H]catechol synthesis in striatal slices induced by high potassium concentration. However, compared to the effects with amphetamine, manganese was much less effective than calcium in supporting the stimulation induced by high potassium concentration. These results show that specific divalent cations can support the stimulation of catechol synthesis induced by amphetamine in striatal slices, and suggest that the entry of these specific ions into cells, presumably dopamine neurons, is involved in this action.     

Eimeria tenella: incomplete excystation in the presence of EDTA in a taurodeoxycholate-based medium

Normally, sporozoites of Eimeria tenella are efficiently excysted in vitro with trypsin and bile salts. However, a one hour treatment at 40 degrees C with a chelator-supplemented excystation medium (purified trypsin and chymotrypsin, taurodeoxycholate and ethylenediaminetetraacetic acid in buffered saline) produced incomplete excystation. The treatment removed the sporocyst plug and left an opened sporocyst containing motile sporozoites, but the release of sporozoites was greatly reduced (less than 12% release). Some of the sporozoites extended a portion of their anterior end through the sporocyst opening then retracted it into the sporocyst. Sporozoites were released when magnesium was added to the chelator-supplemented medium. Manganese was less effective and calcium was ineffective in producing release. Also, sporozoites were released when the incompletely excysted sporocysts were transferred to buffered saline with albumin and this became the basis for a new assay. The assay demonstrated that ethylenediaminetetraacetic acid reduced release in the presence of taurodeoxycholate but not in its absence. Hydrophobic and hydrophilic chelators were tested in the assay. Ethylene-dioxy diethylene-dinitrilotetraacetic acid and 8-hydroxyquinoline were inactive. The chelator 1,10-phenanthroline did not require bile salt to reduce release. The inhibitory effects by phenanthroline were eliminated in the presence of magnesium or manganese, while calcium had no effect. Thus, although certain chelators can inhibit release, a consistent correlation between chelation and inhibition of release has not been established. The application of ethylenediaminetetraacetic acid with taurodeoxycholate as a reversible inhibitor of release is discussed.     

Multinuclear NMR studies of the divalent metal binding site of NADP-dependent isocitrate dehydrogenase from pig heart

The metal activator site of NADP-dependent isocitrate dehydrogenase from pig heart has been probed by using 113Cd and 25Mg NMR as well as manganese paramagnetic relaxation of nuclei in the fast-exchanging ligands alpha-ketoglutarate and adenosine 2'-monophosphate. Cadmium NMR shows that cadmium, bound to the enzyme in the presence of isocitrate, has a resonance at 9 ppm relative to cadmium perchlorate, while the free Cd-isocitrate complex has a resonance at -23 ppm. Comparison with model compounds and previously studied proteins indicates that cadmium is coordinated with six oxygen ligands. Measurements as a function of cadmium concentration give a dissociation constant of 66 microM and a dissociation rate constant of 1.5 X 10(4) s-1 at pH 7.0. 25Mg NMR demonstrates that the line width of the magnesium resonance is increased upon binding to isocitrate dehydrogenase. A further increase in line width is observed upon addition of isocitrate. Measurement of line widths as a function of temperature reveals that in the binary complex between magnesium and enzyme, exchange is the major contributor to broadening while in the ternary complex containing isocitrate, the intrinsic relaxation in the bound state is also important, suggesting an increase in the dissociation rate constant for magnesium from the ternary complex. Paramagnetic relaxation studies of nuclei of alpha-ketoglutarate, bicarbonate, and adenosine 2'-monophosphate locate the divalent metal within the active site. The results with adenosine 2'-monophosphate show that atoms in the adenosine moiety of the coenzyme are at least 8 A from the metal site.(ABSTRACT TRUNCATED AT 250 WORDS)     

Design of a redox-linked active metal site: manganese bound to bacterial reaction centers at a site resembling that of photosystem II

Metals bound to proteins perform a number of crucial biological reactions, including the oxidation of water by a manganese cluster in photosystem II. Although evolutionarily related to photosystem II, bacterial reaction centers lack both a strong oxidant and a manganese cluster for mediating the multielectron and proton transfer needed for water oxidation. In this study, carboxylate residues were introduced by mutagenesis into highly oxidizing reaction centers at a site homologous to the manganese-binding site of photosystem II. In the presence of manganese, light-minus-dark difference optical spectra of reaction centers from the mutants showed a lack of the oxidized bacteriochlorophyll dimer, while the reduced primary quinone was still present, demonstrating that manganese was serving as a secondary electron donor. On the basis of these steady-state optical measurements, the mutant with the highest-affinity site had a dissociation constant of approximately 1 microM. For the highest-affinity mutant, a first-order rate with a lifetime of 12 ms was observed for the reduction of the oxidized bacteriochlorophyll dimer by the bound manganese upon exposure to light. The dependence of the amplitude of this component on manganese concentration yielded a dissociation constant of approximately 1 muM, similar to that observed in the steady-state measurements. The three-dimensional structure determined by X-ray diffraction of the mutant with the high-affinity site showed that the binding site contains a single bound manganese ion, three carboxylate groups (including two groups introduced by mutagenesis), a histidine residue, and a bound water molecule. These reaction centers illustrate the successful design of a redox active metal center in a protein complex.     

Batrachotoxin-activated Na+ channels in planar lipid bilayers. Competition of tetrodotoxin block by Na+

Single Na+ channels from rat skeletal muscle plasma membrane vesicles were inserted into planar lipid bilayers formed from neutral phospholipids and were observed in the presence of batrachotoxin. The batrachotoxin-modified channel activates in the voltage range -120 to - 80 mV and remains open almost all the time at voltages positive to -60 mV. Low levels of tetrodotoxin (TTX) induce slow fluctuations of channel current, which represent the binding and dissociation of single TTX molecules to single channels. The rates of association and dissociation of TTX are both voltage dependent, and the association rate is competitively inhibited by Na+. This inhibition is observed only when Na+ is increased on the TTX binding side of the channel. The results suggest that the TTX receptor site is located at the channel's outer mouth, and that the Na+ competition site is not located deeply within the channel's conduction pathway.     

The relationship among intracellular sodium activity, calcium, and strophanthidin inotropy in canine cardiac Purkinje fibers

The role of sodium and calcium ions in strophanthidin inotropy was studied by measuring simultaneously the electrical, mechanical, and intracellular sodium ion activities in electrically driven cardiac Purkinje fibers under conditions that change the intracellular sodium or calcium level (tetrodotoxin, strophanthidin, high calcium, and norepinephrine). Tetrodotoxin (TTX; 1-5 X 10(-6)M) shifted the action potential plateau to more negative values, shortened the action potential duration, and decreased the contractile tension and the intracellular sodium ion activity (aiNa). The changes in tension and in aiNa caused by TTX appear to be related since they had similar time courses. Strophanthidin (2-5 X 10(-7)M) increased tension and aiNa less in the presence of TTX, and, for any given value of aiNa, tension was less than in the absence of TTX. Increasing extracellular calcium (from 1.8 to 3.3-3.6 mM) or adding norepinephrine (0.5-1 X 10(-6)M) increased tension and decreased aiNa less in the presence than in the absence of TTX. When two of the above procedures were combined, the results were different. Thus, during the increase in aiNa and tension caused by strophanthidin in the presence of TTX, increasing calcium or adding norepinephrine increased tension markedly but did not increase aiNa further. In a TTX-high calcium or TTX-norepinephrine solution, adding strophanthidin increased both tension and aiNa, and the increase in tension was far greater than in the presence of TTX alone. The results indicate that: (a) the contractile force in Purkinje fibers is affected by a change in aiNa; (b) a decrease in aiNa by TTX markedly reduces the inotropic effect of strophanthidin, possibly as a consequence of depletion of intracellular calcium; (c) increasing calcium influx with norepinephrine or high calcium in the TTX-strophanthidin solution produces a potentiation of tension development, even if aiNa does not increase further; and (d) when the calcium influx is already increased by high calcium or norepinephrine, strophanthidin has its usual inotropic effect even in the presence of TTX. In conclusion, the positive inotropic effect of strophanthidin requires that an increase in aiNa be associated with suitable calcium availability.     

盐离子作用下组蛋白变体H2A.Z增强核小体结构的稳定性

真核生物染色质的基本结构组成单元是核小体,基因组DNA被压缩在染色质中,核小体的存在通常会抑制转录、复制、修复和重组等发生在DNA模板上的生物学过程。组蛋白变体H2A.Z可以调控染色质结构进而影响基因的转录过程,但其详细的调控机制仍未研究清楚。为了比较含有组蛋白变体H2A.Z的核小体和常规核小体在盐离子作用下的稳定性差异,本文采用Förster共振能量转移的方法检测氯化钠、氯化钾、氯化锰、氯化钙、氯化镁等离子对核小体的解聚影响。实验对Widom 601 DNA序列进行双荧光Cy3和Cy5标记,通过荧光信号值的变化来反映核小体的解聚变化。Förster共振能量转移检测结果显示:在氯化钠、氯化钾、氯化锰、氯化钙和氯化镁作用下,含有组蛋白变体H2A.Z的核小体解聚速度相比于常规核小体要慢,且氯化钙、氯化锰和氯化镁的影响更明显。电泳分析结果表明,在75℃条件下含有组蛋白变体H2A.Z的核小体的解聚速率明显低于常规核小体。采用荧光热漂移检测(fluorescence thermal shift analysis , FTS)进一步分析含有组蛋白变体H2A.Z核小体的稳定性,发现两类核小体的荧光信号均呈现2个明显的增长期,含有组蛋白变体H2A.Z核小体的第1个荧光信号增速期所对应的温度明显高于常规核小体,表明核小体中H2A.Z/H2B二聚体的解聚变性温度要高于常规的H2A/H2B二聚体,含有组蛋白变体H2A.Z核小体的热稳定性高。研究结果均表明,含有组蛋白变体H2A.Z的核小体的结构比常规核小体的结构稳定。     

Genetic effect on uptake of selected nutrients in some rice (O. sativa L.) varieties in phosphorus deficient soils

The influence of genes on the uptake by rice plants of certain macro- and micronutrients (calcium, magnesium, iron, manganese and zinc) was studied, by diallel (7 × 7) analysis, in P deficient upland soil. Both additive and dominant gene effects, with a preponderance of the former, were found to be responsible for the uptake of all the elements studied. Local varieties were found to be not only good yielders but also much more efficient in element uptake. Heterotic effects were observed in various crosses with respect to the uptake of all the aforementioned nutrients. Statistical analysis indicated that while the uptake of iron and zinc were negatively correlated, the uptake of manganese and calcium, manganese and zinc, calcium and magnesium and calcium and zinc were positively correlated.