Effect of Ca on CO2 corrosion properties of X65 pipeline steel

The effect of Ca²⁺ on CO₂ corrosion to X65 pipeline steel was investigated in the simulated stratum water of an oil field containing different concentrations of Ca²⁺. It is found that Ca²⁺ can enhance the corrosion rate, especially in the Ca²⁺ concentration from 256 to 512 mg/L, which can be attributed to the growing grain size and loosing structure of corrosion scales with increasing Ca²⁺ concentration. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) investigations reveal that a complex carbonate (Fe, Ca)CO₃ forms at high Ca²⁺ concentration due to the gradual replacement of Fe²⁺ in FeCO₃ by Ca²⁺.     

Effects of La3+ and Gd3+ on Ca2+ influx in rat hepatoma H-35 cells

Effects of La³⁺ and Gd³⁺ on Ca²⁺ influx were investigated in rat hepatoma H-35 cells by measuring the initial rate of⁴⁵Ca²⁺ uptake. It was found that the maximum initial rate of Ca²⁺ uptake was increased six-to ten-fold at low concentrations of La³⁺ and Gd³⁺. Kinetic analyses by measuring the initial rate of Ca²⁺ influx at different external Ca²⁺ concentrations indicated the existence of two intracellular exchangeable components in the basal Ca²⁺ system, with low and high affinities for Ca²⁺, and only one class of Ca²⁺ binding sites was observed in the La³⁺-or Gd³⁺-treated cells. For high affinity, La³⁺ and Gd³⁺ increased both kinetic parametersK _m andV _max of basai Ca²⁺ influx. La³⁺ and Gd³⁺ compete directly with Ca²⁺ for Ca²⁺ binding site for low affinity. The kinetics is competitive.     

Mg2+-induced LHC II aggregation in thylakoid membrane

Mg²⁺-induced changes in 77K fluorescence spectra of wheat thylakoid membranes were analyzed by a Gaussian deconvolution program. All spectra were fitted well with 7 Gaussian sub-bands. The sub-band areas for the LHC H macroaggregate (F₆₉₉) and PS II (F₆₈₅ and F₆₉₅) were increased and those for the LHC II trimer (F₆₈₁) and PS I (F₇₂₉ and F₇₄₀) were decreased by Mg²⁺. Moreover, it was found that the sub-band area ratio for F₆₉₉ over F₆₈₁ was dramatically enhanced by Mg²⁺ by 1.72 times. It was concluded that the LHC II trimer in thylakoid membranes could be aggregated and transformed into its macroaggregate by Mg²⁺ on a large scale. The possible implication of the Mg²⁺-induced LHC II aggregation was also discussed.     

Heat and hyposmotic stimulation increase in [Ca^2＋]i by Ca^2＋ influx in rat synoviocytes

Rheumatoid arthritis （RA）, which is marked by inflammatory synovitis, is a common, chronic autoimmune-disease, whose pathogenesis is complex and still unclear. In order to explore the effects of heat and hyposmotic stimuli on synoviocytes in rheumatoid arthritis, the changes of [Ca^2＋]i induced by heat, hyposmotic and 4α-PDD stimuli were observed in synoviocytes. [Ca^2＋]i elevation induced by heat 28℃, hyposmotic and 4α-PDD stimuli is found to be positively relative to increasing temperature, decreasing osmolality and rising concentration of 4α-PDD. Results show that there is reciprocity among these stimuli and desensitization, and that [Ca^2＋]i elevation depends on Ca^2＋ influx, but not necessarily links to Ca^2＋ release from intracellular stores and voltage-dependent Ca^2＋ channel in synoviocytes. The above characteristics of Ca^2＋ influx are similar to those of TRPV4. A probable mechanism has been suggested that heat and hyposmotic stimulation might increase the level of [Ca^2＋]i by activating the TRPV4-like channel and Ca^2＋ influx in the synoviocytes.     

Ca2+ signals induced from calcium stores in pancreatic islet β cells

In single rat pancreatic β cells, using fura-2 microfluorometry to measure [Ca²⁺]i response upon different stimuli, the ways of calcium regulation have been studied. When the extracellular calcium concentration was 2.5 mmol/L, either 60 mmol/L KCl, 20 mmol/L D-glucose or 0.1 mmol/L tolbutamide induced increase in [Ca²⁺]i. Such increase in [Ca²⁺]i was absent when the same stimuli were applied under zero extracellular calcium. These results indicate that the increase of [Ca²⁺]i is induced by the activation of voltage-dependent calcium channels in β cells. The manifold forms of [Ca²⁺]i change induced by glucose imply that the effects of glucose are complex. 5 mmol/L caffeine or 5 mmol/L MCh increase the [Ca²⁺]i, which is independent of the external calcium, suggesting that [Ca²⁺]i can be regulated by Ca²⁺ release from not only the IP₃-sensitive but also the ryanodine sensitive calcium stores in β cells. The latency of Ca responses for IP₃ pathway (5 s) is faster than that for ryanodine pathway (30 s). It is concluded that there are multiple calcium stores in rat pancreatic β cells.     

Effect of calcium ions on the secondary structures of photosystem II and its relations with photoinhibition

Calcium ions play an important role in the oxygen-evolving process of photosystem II as demonstrated in many experiments. The changes of the secondary structures of PS II induced by the depletion of Ca²⁺ were reported. The results indicated that the removal of Ca²⁺ led to the transition of ahelix to turns and sheet structures. While Ca²⁺ was re-added to the media, only the structures changed to turns could be recovered. The protein conformational changes of PS II during the donor side photoinhibition induced by the depletion of ca²⁺ were also studied. This showed that the protein conformational changes differed between the control and Ca²⁺-depleted samples in a short period of illumination (within 10 min). However, the changes became similar when the illumination time was increased.     

The new sideway of CNTF signal transduction pathway

The action of ciliary neurotrophic factor (CNTF) on intercellular free Ca²⁺ concentrations [Ca²⁺]_i induced by glutamate (Glu) in primary cultured hippocampal neurons were detected with Fura2/AM, a Ca²⁺-sensitive fluorophore, and the morphological influence of G-protein on it was objected. Glu could induce rapid increase of [Ca²⁺]_i in hippocampal neurons. CNTF had no significant action on [Ca²⁺]_i in resting hippocampal neurons. However, after incubation of CNTF for 5 min, the increase of [Ca²⁺]_i in hippocampal neurons rapidly induced by Glu was inhibited. Pretussis toxin (PTX)-sensitive G protein could block the action. These results indicate that a new non-genomic rapid sideway might exist in the upper stream of CNTF signal transduction pathway, which was related to Ca²⁺ signal transduction. Keywords:     

Mechanisms of peroxynitrite-induced [Ca2+]i increase in single neuronal cell

The mechanism of peroxynitrite (ONOO⁻)-induced [ca²⁺]_i increase in single MN9D cell (Dopaminergic neuroblastoma cell line) was studied by using Fura-2 microfluorometric technique. The results show that ONOO⁻ caused a rapid increase of [Ca²⁺]_i when ONOO₋ was puffed to the cell. Removing Ca²⁺ from the bath or using calcium channel antagonist (CdCl₂, Nifedipine) greatly inhibited the [Ca²⁺]_i increase induced by ONOO⁻¹, suggesting that the opening of L-Ca²⁺ channel makes a great contribution to the [Ca²⁺]_i increase. The effect of sulfhydryl reductive agent (DTT) on ONOO⁻-induced [Ca²⁺]_i increase suggests that ONOO⁻-activating L-Ca²⁺ channel is partly related to its oxidative speciality.     

Nitric oxide suppresses stomatal opening by inhibiting inward-rectifying K<Stack><Subscript>in</Subscript><Superscript>+</Superscript></Stack> channels in <Emphasis Type="Italic">Arabidopsis</Emphasis> guard cells

We explore nitric oxide （NO） effect on K^＋in, channels in Arabidopsis guard cells. We observed NO inhibited K^＋in, currents when Ca^2＋ chelator EGTA （Ethylene glycol-bis（2-aminoethylether）-N,N,N′,N;tetraacetic acid） was not added in the pipette solution; K^＋in currents were not sensitive to NO when cytosolic Ca^2＋ was chelated by EGTA. NO inhibited the Arabidopsis stomatal opening, but when EGTA was added in the bath solution, inhibition effect of NO on stomatal opening vanished. Thus, it implies that NO elevates cytosolic Ca^2＋ by activating plasma membrane Ca^2＋ channels firstly, then inactivates K^＋in, chartnels, resulting in stomatal opening suppressed subsequently.     

Role of Ubisch bodies secreted by tapetum in Ca2+ transprot

The distribution of Ca²⁺ in the anthers of wheat was observed using cytochemical method of potassium antimonite. At the later tetrad stage, Ubisch bodies carrying Ca²⁺ were observed on the inner surface of tapetum, in anther locule and on pollen surface. The Ubisch bodies contacted with pollen, and Ca²⁺ began to accumulate on pollen surface. At the uninucleate pollen stage, abundant Ubisch bodies were distributed in anther locule, and the amount of Ca²⁺ on pollen surface increased. At the mature pollen stage a large amount of Ca²⁺ ions were localized on the inner surface of tapetum, the surface of pollen and Ubisch bodies. In the pollen wall, Ca²⁺ precipitates arranged in radial lines. These results demonstrated that Ubisch bodies were involved in Ca²⁺ transport from anther wall to pollen surface at some developmental stages of anther.     

Rearrangements of microtubule cytoskeleton in stomatal closure of <Emphasis Type="Italic">Arabidopsis</Emphasis> induced by nitric oxide

NO （nitric oxide）, known as a key signal molecule in plant, plays important roles in regulation of stomatal movement. In this study, microtubule dynamics and its possible mechanism in the NO signal pathway were investigated. The results were as follows： （i） In vivo stomatsl aperture assays revealed that both vinblastine （microtubule-disrupUng drug） and SNP （exogenous NO donor） prevented stomatsl opening in the light, and vinblastine even could enhance the inhibitory effect of SNP, whereas tsxol （a microtubule-stsbilizing agent） was able to reduce this effect; （ii） microtubules in the opening Arabi-dopsis guard cells expressing GFP：a-tubulin-6 （AtGFP：a-tubulin-6） were organized in parallel, straight and dense bundles, radiating from the ventral side to the dorsal side, and most of them were localized perpendicularly to the ventral wall; （iii） under the same environmental conditions, treated with SNP for 30 min, the radial arrays of microtubules in guard cells began to break down, twisted partially and be- came oblique or exhibited a random pattern; （iv） furthermore, the involvement of cytosolic Ca^2＋ in this event was tested. Stomatal aperture assays revealed that BAPTA-AM （a chelator of Ca^2＋） greatly suppressed the effect of NO on stomatal closure; however, it did not show the same function on stomatal closure induced by vinblastine. When BAPTA-AM was added to the SNP-pretreated solution, the SNP-induced disordered microtubulue cytoskeleton in guard cells underwent rearrangement in a time-dependent manner. After 30 min of treatment with BAPTA-AM, the cortical microtubules resumed the original radial distribution, almost the same as the control. All this indicates that NO may promote rearrangement of microtubule cytoskeleton via elevation of [Ca^2＋]cyt （free Ca^2＋ concentration in the cytoplasm）, finally leading to stomatsl closure.     

Research at channel level on the effect of LaCl3 on Radish (Raphanus satirus L.) vacuolar membrane

We recorded slow vacuolar (SV-type) channel currents of Radish vacuoles successfully for the first time by using the whole-vacuolar patch-clamp recording mode. SV- type currents would increase and threshold potentials of activation would shift towards more negative values with the increase of concentrations of cytosolic Ca²⁺. When 2.5 mmol/ L LaCl₃ and 4 mmol/L EGTA were added to bath solutions, SV-type currents were suppressed remarkably. Then adding LaCl₃ with different concentrations to pipette solutions, we found that LaCl₃ with higher concentrations (＞4 ´ 10^-7 mol/L) had a strong inhibitory effect on SV-type currents, while LaCl₃ with lower concentrations (≤4 ´ 10^-7 mol/L) promoted channel currents. This promoting effect provides an important basis at channel level for researching further the effects of rare earth on physiological activities of plants and the production-increase effects of rare earth fertilizers on crops.     

Thermal stability of oxygen evolution in photosystem Ⅱ core complex in the presence of digalactosyl diacylglyceroli

The influence of digalactosyldiacylglycerol (DGDG), one of the photosynthetic membrane lipids, on heat inactivation of the process of oxygen evolution has been studied in vitro in photosystem Ⅱ (PSⅡ) core complex. It was found that the temperature of semi-inactivation of oxygen evolution in the complex increased from 40.0 to about 43.0℃ in the presence of DGDG with 5-min heat treatment in the dark. Furthermore, when PSⅡ core complex was incubated for 5 min at 45.0℃, the oxygen evolution in the complex was completely lost, whilst the DGDG-complexed PSⅡ core complex still retained a 16% of activity (100% for 25.0℃). In addition, a 1-h incubation at 38.0℃ inactivated absolutely the oxygen evolution for the PSⅡ core complex. By contrast, there remained about 20% of activity (zero time for 100%) for the complex in the presence of DGDG under the same condition. These results indicate a new role of DGDG in the protection of PSⅡ core complex against the deleterious effects of temperature. It was most likely that DGDG-mediated stability toward thermal denaturation of oxygen evolution in PSⅡ core complex is due to the protective effect of DGDG on the release of the 33 kD protein from PSⅡ core complex.     

Depletion of phosphatidyl-glycerol head-group induces changes in oxygen evolution and protein secondary struc-tures of photosystem Ⅱ

The techniques of oxygen electrode polarogra-phy and Fourier transform infrared (FT-IR) spectroscopy were employed to explore the roles of polar head-group of phosphatidylglycerol (PG) molecules in the functional and structural aspects of photosystem Ⅱ (PS Ⅱ) through enzymatic approach. It was shown that the depletion of PG by treatment of phospholipase C (PLC) on PS Ⅱ particles caused the inhibition of oxygen evolving activity in PS Ⅱ. This effect also gave rise to changes in the protein secondary structures of PS Ⅱ, that is, an increase in a-helical conformation which is compensated by the loss of p-strand structures. It revealed that the head-group of PG molecules plays an important structural role in the maintenance of normal structure of PS Ⅱ proteins, which is required to maintain the appropriate physiological activity of the PS Ⅱ complex such as the oxygen evolving activity. It is suggested that there most probably exist hydrogen-bonding interactions between PG molecules and PS Ⅱ proteins.     

Callus formation in relation to changes of the membrane Ca2+ in the graft unions ofGinkgo biloba L.

The relationship between the callus formation and intracellular Ca²⁺ at the early stage of development of graft unions inGinkgo biloba L. was investigated. On the second day after grafting, part of the undamaged living cells at the graft interface of the stock and scion in the regions of the cortex and pith began to dedifferentiate or divide. 8 d after grafting, a great number of callus cells were produced from the cortex and phloem, while callus bridges linking the stock with scion formed between the callus cells of the graft partners from the cortex. A membrane Ca²⁺ probe, chlortetracycline (CTC), was used to locate the intracellular Ca²⁺ distribution and it was found that the cortical and pith parenchyma cells were the first to show remarkably increased CTC-Ca²⁺ fluorescence, suggesting that the cortical and other parenchyma cells play a leading role at the early stage of development of graft unions by earlier dedifferentiation and more rapid production of callus cells.     

Effect of Mn cluster on the formation of superoxide radicals in photoinhibition of photosystem Ⅱ

To further realize the action of superoxide radicals (O₂^{− .}) in photoinhibition of photosystem Ⅱ (PSⅡ), we employed 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a spin trap, associated with EPR spectroscopy, to study the effect of illumination time on O₂^{− .} formation during high light photoinhibition in PSⅡ membranes and Mn-depleted PSⅡ membranes. Results indicated that the removal of Mn cluster from PS
membranes has a strong influence on the dynamics of superoxide formation. The relative mechanism was also discussed. These novel findings may further promote the studies of the structure and function of PSⅡ and the mechanism of photoinhibition.     

H-ATPase in the plasma membrane of Arabidopsis pollen cells is involved in extracellular calmodulin-promoted pollen germination

In this paper, the role of the plasma membrane (PM) H⁺-ATPase in extracellular calmodulin (CaM)-promoted pollen germination and in tube growth of Arabidopsis thaliana was investigated. Pollen germination, pollen tube growth rate, free cytosolic Ca²⁺ concentration ([Ca²⁺]_cyt) and Ca²⁺ channel activity in the PM of pollen cells were measured. In response to fusicoccin or CaM treatment, in vitro pollen germination and pollen tube growth rate, [Ca²⁺]_cyt and activity of a hyperpolarization-activated Ca²⁺-permeable channel increased. Sodium vanadate inhibited the promotion of these parameters by extracellular CaM. The results suggest that H⁺-ATPase may be involved in extracellular CaM-regulated pollen germination and in tube growth by modulation of the hyperpolarization-activated Ca²⁺ channel in the PM of A. thaliana pollen cells.     

Protection of phosphatidylcholine to photosystem Ⅱ membrane during heat treatment

Photosystem Ⅱ membrane was reconstituted with phosphatidylcholine (PC) with different kinds of fatty acyl chains and the protection of PC to photosystem Ⅱ (PS Ⅱ)membrane during heat treatment was investigated using oxygen electrode, variable fluorescence and circular dichroism (CD) spectroscopy. Heat treatment decreased the oxygen evolution rate and the F′v/Fm′ ratio of PS Ⅱ membrane and influenced CD spectra of PS Ⅱ membrane, but PC inhibited the effect of heat treatment on the oxygen evolution rate, the F′v/F′m ratio and CD spectra of PS Ⅱ membrane. The results indicate that PC can protect PS Ⅱ membrane against heat treatment and the alterations in the unsaturated fatty acid extent in PC can cause the changes of the protection ability.