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

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.     

Phosphatidylglycerol effect on oxygen-evolving activity in Ca2+-depleted photosystem Ⅱ

The effect of anionic phosphatidylglycerol (PG) on oxygen evolution in a photosystem Ⅱ (PSⅡ) particle depleted of Ca2+ (designated dCaPSⅡ) has been investigated. The major finding is the observation of a new role of PG in the PSⅡ function. That is, PG restores nearly the lost oxygen evolution in dCaPSⅡ particle owing to Ca2+ depletion to the levels in intact PSⅡ. Furthermore, there is a stimulation of oxygen-evolving activity in the dCaPSⅡ complexed with PG in the presence of exogenous CaCl2, which PG enhances increasingly oxygen evolution with increasing CaCl2 concentration. It is suggested that PG-induced oxygen evolution recovery of dCa PSⅡ particle results from resumption of normal structure in protein by PG effect, whereas the enhancement of oxygen evolution in complex subject to CaCl2 is ascribed to the optimization of such a structure due to coordination complex formation of Ca2+ ions with PG.     

Relationship among Photosys-tem Ⅱ carbonic anhydrase,extrinsic polypeptides and manganese cluster

Effects of Photosystem Ⅱ (PS Ⅱ) extrinsic polypeptides of oxygen-evolving complex and manganese clusters on PSⅡ carbonic anhydrase (CA) were studied with spinach PSⅡ membranes. The result supported that membrane-bound CA is located in the donor side of PSⅡ. The extrinsic polypeptides played an important role of maintaining CA activity. After removing manganese clusters, oxygen evolution activity was inhibited, but PSⅡ-CA activity was unchanged. It was concluded that CA activity is independent of the presence of manganese clusters, and was not directly correlated with oxygen evolution activity.     

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.     

Comparison of the Photosynthetic Characteristics of Two Developmental Stages in Nostoc sphaeroides Kutzing （Cyanophyta）

The photosynthetic activities between two main developmental stages, colony and hormogonium, of the edible cyanobacterium Nostoc sphaeroides Kutzing, were compared. Hormogonia have a higher content of chlorophyll than that of colonies. It showed that the ratios of phycocyain （PC）, allophycocyain （APC） and phycoerythrocyanin （PEC） in hormogonia and colonies were different. The room temperature chlorophyll fluorescence, 77 K chlorophyll fluorescence, measurements of PSⅠand PS Ⅱ activities all showed that colony has higher photosynthetic competence than hormogonia. Hormogonia had a higher respiration rate than colony, while their maximum photosynthetic oxygen evolution rates were very close. The responses of hormogonia and colonies to high light illuminations also were different. Both of their oxygen evolution rates decreased quickly with the prolonged high light illumination, but hormogonia can keep relatively higher PSⅡ activity （Fv/Fm） than that of colonies. The results suggested that colony was photosynthetically more competent than hormogonia, while the ability of hormogonia to tolerate high light illumination was higher than that of colony.     

Increase in electron transfer activity in photosystem Ⅱ of spinach thylakoids caused by conversion of phosphatidyl- glycerol to phosphatidic acid molecules

The techniques of oxygen electrode polarography, sodium dodecyl sulfate-polyacryamide gel electrophoresis (SDS-PAGE) and thin layer chromatography (TLC) were employed to investigate the effect of phospholipase D treatment on physiological function of spinach thylakoids. It was shown that the phospholipase D treatment on thylakoid resuited in the degradation of phosphatidylglycerol (PG) and occurrence of phosphatidic acid (PA). The changes of PG to PA molecules caused an increase in oxygen evolution in photosystem Ⅱ (PS Ⅱ), which was accompanied by an uncoupling effect on thylakoid membrane. It was revealed that the head-groups of PG molecules play an important role in themaintenance of the appropriate physiological activity of thylakoid membrane.     

Depletion of phosphatidylglycerol head-group induces changes in oxygen evolution and protein secondary structures of photosystemⅡ

The techniques of oxygen electrode polarography 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 photosystemⅡ(PSⅡ) through enzymatic approach. It was shown that the depletion of PG by treatment of phospholipase C (PLC) on PSⅡ particles caused the inhibition of oxygen evolving activity in PSⅡ. This effect also gave rise to changes in the protein secondary structures of PSⅡ, that is, an increase in α-helical conformation which is compensated by the loss of β-strand structures. It revealed that the head-group of PG molecules plays an important structural role in the maintenance of normal structure of PSⅡ proteins, which is required to maintain the appropriate physiological activity of the PSⅡ complex such as the oxygen evolving activity. It is suggested that there most probably exist hydrogen-bonding interactions between PG molecules and PSⅡ proteins.     

Co-oxidation of arsenic(Ⅲ) and iron(Ⅱ) ions by pressurized oxygen in acidic solutions

The co-oxidation of As(Ⅲ) and Fe(Ⅱ) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and2.0 MPa at a temperature of 150℃. It was confirmed that without Fe(Ⅱ) ions, As(Ⅲ) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200℃ and an oxygen pressure up to 2.0 MPa. Fe(Ⅱ) ions in the solutions did have a catalysis effect on the oxidation of As(Ⅲ), possibly attributable to the production of such strong oxidants as hydroxyl free radicals(OH·) and Fe(IV) in the oxidation process of Fe(Ⅱ). The effects of such factors as the initial molar ratio of Fe(Ⅱ)/As(Ⅲ), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(Ⅲ) and Fe(Ⅱ) were studied. It was found that the oxidation of As(Ⅲ) was limited in the co-oxidation process due to the accumulation of the As(Ⅲ) oxidation product, As(V), in the solutions.     

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.     

Responses of ephemeral plant germination and growth to water and heat conditions in the southern part of Gurbantunggut Desert

Ephemeral plants in the southern part of Gurbantunggut Desert were systematically monitored from 2002 to 2004 and the meteorological data and soil moisture during the same period were analyzed. The results show that the ephemeral plants germination and growth are sensitive to the changes of water and heat condition. The time for daily temperature over 0℃ in early spring in 2003 was delayed nearly 10 d compared with that in 2002, while the soil water changed little in the same period. Observation showed that there were 28 ephemeral species germinated in 2002, their life period was about 70 d in spring, and the maximum cover of ephemeral synusia reached 46.4%. However, only 17 ephemeral species germinated in 2003, their life period was about 50 d in spring, and their maximum cover was only 20.8%. The height of ephemeral plants was significantly higher in 2002 than that in 2003. It can be seen that ephemeral plant germination and growth in spring are strongly dependent on temperature. The changes of water conditions can affect ephemerals germination and growth as well. Because no heavy precipitation occurred during summer in 2002, only a few ephemerophytes were observed in autumn after ephemerals completed their life circle in early spring. However, about 60 mm precipitation was recorded from July to August both in 2003 and in 2004. Some ephemerals such as Erodium oxyrrhynchum and Carex physodes, etc. covered the dune surface rapidly with a cover 〉10%. Therefore, the ephemerals not only germinate in autumn after the early spring, some species may germinate in summer if adequate rainfall occurs. The study on responses of ephemerals growth to water and heat conditions not only has a certain ecological significance but also contributes a better understanding to the effect of climate changes on the desert surface stability.     

Protection of phosphatidyl-choline 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 dichro-ism (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.     

Phosphatidylglycerol effect on oxygen-evolving activity in Ca2+-depleted photosystem II

The effect of anionic phosphatidylglycerol (PG) on oxygen evolution in a photosystem II (PS II ) particle depleted of Ca²⁺ (designated d_CaPSII ) has been investigated. The major finding is the observation of a new role of PG in the PSII function. That is, PG restores nearly the lost oxygen evolution in d_caPS II particle owing to Ca²⁺ depletion to the levels in intact PS II. Furthermore, there is a stimulation of oxygen-evolving activity in the d_CaPSII complexed with PG in the presence of exogenous CaCl₂, which PG enhances increasingly oxygen evolution with increasing CaCl₂ concentration. It is suggested that PG-induced oxygen evolution recovery of d_Ca PS II particle results from resumption of normal structure in protein by PG effect, whereas the enhancement of oxygen evolution in complex subject to CaCl₂ is ascribed to the optimization of such a structure due to coordination complex formation of Ca²⁺ ions with PG.     

Geothermal field and thermotectonic evolution in Southern South Yellow Sea Basin

Based on the available borehole temperature data and measurements of thermal conductivities on 10 core samples in the Southern South Yellow Sea Basin, 8 heat flow values are obtained. The results show that the mean values of temperature gradient and heat flow are 28.6“C/km and 69 mW/m^2, respectivdy. The thermal history reconstruction from the inversion of vitrinite reflectance data, using the temperature-gradient method, indicates that the highest paleo-heat flow occurred at the end of the Mesozoic, and then the barn began to cool to present day. Tectonic subsidence analysis shows that the basin experienced at least four episodes of quick subsidence since the late Paleozoic and that the tectonic evolution was quite strong and complex.     

柴油机纯氧燃烧过程及缸内喷水影响的模拟研究

针对高压共轨柴油机搭建流体动力学仿真模型,研究不同进气氧体积分数对柴油机纯氧燃烧过程的影响,并验证缸内喷水对热效率的优化能力。结果表明,氧含量的提高增加了缸内比热比,使压缩行程缸内压力及温度提高,并促进缸内燃烧反应,进一步提升缸内湍流强度,燃烧相位提前;在5℃A ATDC(上止点后)向缸内喷入160℃的高温高压水,可实现对缸内燃烧过程的控制,并通过吸收燃烧放热、汽化膨胀,推动活塞做功,可提高热效率约3.75%。     

复盐分解法制备纳米二氧化钛及其光催化降解偶氮染料性能研究

采用复盐热分解法制备了纳米二氧化钛,对其形貌和晶相进行了分析。600~700℃热分解产物为单一的锐钛矿相,晶粒尺寸约为25 nm。以双胺绿B等大分子量的偶氮染料分子作为光催化降解模型,评价了其在通氧条件下的光催化活性。结果表明,600℃热分解得到的光催化剂活性最好,对初始浓度100 mg/L双胺绿B溶液,通氧条件下90min的降解率为100%,与Degussa P25相当。     

Novel sintering behavior of polystyrene nano-latex particles in filming process

Filming process of polystyrene nano-latex (NPS) particles was studied by a combination of various methods. For a constant annealing time of 1 h, the AFM images showed that the deformation and sintering temperatures for NPS particles were ca. 90℃ and 100℃ respectively. In spin-lattice relaxation measurements of solid state NMR, it is found that T_1L, T_1S and I_1L/I₀ increased significantly after annealing at 90℃ and above. DSC results showed that there was an exothermic peak near T_g after annealing for 1 h at the selected temperatures below 95℃; otherwise, the exothermic peak disappeared after annealing at 100℃ or above. The apparent density of NPS increased suddenly in the temperature range. The results implied that the macromolecules in NPS particles are in a confined state with higher conformational energy and less cohensional interactions which are the drive force for the sintering at a lower temperature compared with the multichain PS particles and the bulk polymer.     

Sea surface temperature record from the north of the East China Sea since late Holocene

Using the alkenone paleotemperature index U37^k, a high-resolution sea surface temperature （SST） record since 3600 a BP was reconstructed from the mud area in the north of the East China Sea. Combining with the grain size distribution curve of sensitive grain size group, which may reflect the East Asia Winter Monsoon activity, the palaeoenvironmental evolution cycle throughout the late Holocene in the area was obtained. The marine environment evolution during the last 3600 years displays a five-stage trend. （1） Temperature descending period from 0.85 cal. ka BP to present. The maximum temperature decrease amplitude is 2℃. The winter monsoon intensified and ＇Little Ice Age＇ were recorded in this period. （2） Warming period from 1.90 to 0.85 cal. ka BP. The mean temperature increase amplitude is 0.8℃. The Sui-Tang warming period was recorded at about 0.85--1.35 cal. ka BP and a prominent cooling event was recorded at 1.4 cal. ka BP in this period. （3） Temperature descending period from 2.55 to 1.90 cal. ka BP. Temperature cooling amplitude is 0.9℃. This period is coincident with an integrated temperature circle recorded in the Antarctic ice core, with the temperature changes from a slow cooling stage to a rapid warming stage. （4） Temperature comparatively stable with a little ascending period from 3.2 to 2.55 cal. ka BP. Temperature warming amplitude is 0.3℃. This period is coincident with the temperature fluctuant ascending period recorded in Antarctic ice core. （5） Temperature comparatively stable with little descending period from 3.6 to 3.2 cal. ka BP. This period corresponds with the temperature fluctuant cooling period recorded in Antarctic ice core. Basically, those five periods were coincident with the Antarctic ice core record. During the global cooling stage, the SST change in the continental shelf sea can be adjusted simultaneously.