Structural Aspects of Photosystem I from Dunaliella salina

A native PSI complex and a PSI core complex have been isolated from the halophilic green alga, Dunaliella salina. The composition and properties of these complexes are similar to previously described PSI complexes from spinach membranes. By growth on ¹⁴C-NaHCO₃, it has been possible to isolate uniformly labeled ¹⁴C-PSI complexes in order to determine PSI subunit stoichiometry. This analysis has shown a ratio of one copy of three low molecular weight subunits (22,000; 15,000; 8,000) per two copies of high molecular weight subunits (84,000). Using a ¹⁴C-labeled cytochrome b₆-f complex as an internal protein standard, it has been possible to estimate the molecular weight of a PSI core complex as about 330,000. This complex contains one P700, two 84,000 subunits, and one subunit of 22,000, 15,000, and 8,000.     

Salt-Induced Metabolic Changes in Dunaliella salina

An increase of medium NaCl concentration induces Dunaliella cells to evolve O₂ photosynthetically even in the absence of CO₂. This NaCl-induced O₂ evolution may reflect the induced conversion of reserve carbohydrate to glycerol. The quantum yield for the NaCl-induced O₂ evolution, in the absence of CO₂, is 1.5-fold higher than that obtained for CO₂ fixation. Since the synthesis of glycerol from reserve carbohydrate in the absence of CO₂ requires only 0.5 ATP/NADPH, whereas photosynthesis requires at least 1.3 ATP/NADPH, it is concluded that the ATP/2e⁻ ratio coupled to NADP reduction in Dunaliella is lower than required for CO₂ fixation.     

Changes in Photosystem Stoichiometry in Response to Environmental Conditions for Cell Growth Observed with the Cyanophyte Synechocystis PCC 6714

Changes in photosystem stoichiometry in response to shift ofenvironments for cell growth other than light regime were studiedwith the cyanophyte Synechocystis PCC 6714 in relation to thechange induced by light-quality shift. Following two environment-shiftswere examined: the shift of molecular form of inorganic carbonsource for photosynthesis from CO₂ to HCO₃^– (CO₂ stress)and the increase in salinity of the medium with NaCl (0.5 M)(Na⁺ stress). Both CO₂ and Na⁺ stresses induced the increasein PSI abundance resulting in a higher PSI/PSII stoichiometry.CO₂ stress was found to elevate simultaneously Cyt c oxidaseactivity (V_max). The feature was the same as that caused bylight-quality shift from preferential excitation of PSI to PSII(light stress) though the enhancement by either stress was smallerthan that by light stress. Under our experimental conditions,PSI/PSII stoichiometry appeared to increase at a fairly constantrate to the basal level even when the basal level had been differentlydetermined by the light-quality. Enhancing rates for PSI/PSIIstoichiometry and for Cyt c oxidase activity were also similarto each other. Since the two stresses affect the thylakoid electrontransport similarly to the shift of light-quality, we interpretedour results as follows: three environmental stresses, CO₂, Na⁺,and light stresses, cause changes in electron turnover capacityof PSI and Cyt c oxidase under a similar, probably a common,mechanism for monitoring redox state of thylakoid electron transportsystem. ¹On leave from Department of Biology, College of Natural Science,Kyngpook National University, Taegu 702-701, Korea. ₂Present address: Department of Marine Bioscience, Fukui Pre-fecturalUniversity, Obama, Fukui, 917 Japan.     

Dynamics of Photosystem II and Its Light Harvesting System in Response to Light Changes in the Halotolerant Alga Dunaliella salina

A photosystem two (PSII) core complex consisting of five major polypeptides (47, 40, 32, 30, and 10 kilodaltons) and a light harvesting chlorophyll a/b complex (LHC-2) have been isolated from the halotolerant alga Dunaliella salina. The chlorophyll and polypeptide composition of both complexes were compared in illuminated and dark-adapted cultures. Dark adaptation is accompanied by a decrease in the chlorophyll a to chlorophyll b (Chl a/Chl b) ratio of intact thylakoids without any change in total chlorophyll. These changes occur with a half-time of 3 hours and are reversed upon reillumination. Analyses of PSII enriched membrane fragments suggest that the decrease in the Chl a/Chl b is due partly to an increase in the Chl b content of LHC-2 and partly to changes in the relative levels of the two complexes. Apparently during dark adaptation there is: (a) a net synthesis of chlorophyll b, (b) removal of PSII core complexes resulting in a 2-fold drop in the PSII cores to LHC-2 chlorophyll ratio. These changes should dramatically increase the light harvesting capacity of the remaining PSII reaction centers. Presumably this adjustment of antenna size and composition is a physiological mechanism necessary for responding to shade conditions. Also detected, using ³²P, are light-induced phosphorylation of the LHC-2 (consistent with the ability to undergo State transitions) and of the 40 and 30 kilodalton subunits of the PSII core complex. These observations indicate that additional mechanisms may also exist to help optimize the interception of quanta during rapid changes in illumination conditions.     

Cr3+对盐藻(Dunaliella salina)生长及营养品质的影响

以盐藻Dunaliella salina为材料,设定0ìg·L^-1、3ìg·L^-1、12ìg·L^-1、50ìg·L^-1、200ìg·L^-1和800ìg·L^-16个添加Cr³⁺浓度处理,分析测定了不同铬浓度下盐藻的生物量(细胞密度).蛋白质、â胡萝卜素和可溶性糖含量.研究结果表明,中低量添加Cr³⁺对盐藻的生长有一定的促进作用,在50ìg·L^-1和200ìg·L^-1Cr³⁺条件下,盐藻的生物量高于对照,中低量添加Cr³⁺对盐藻的生长有一定的促进作用,盐藻蛋白质含量比对照分别提高3.06%和6.55%,Cr³⁺浓度在200ìg·L^-1时,盐藻的â胡萝卜素和可溶性糖含量比对照分别提高3.93%和2.38%,适当添加Cr³⁺可提高盐藻蛋白质、â胡萝卜素和可溶性糖含量,有效改善盐藻的营养品质.     

锌对盐藻生长与物质积累的调控作用

实验研究了不同浓度的锌对盐藻细胞生长与物质积累的调控作用。结果表明,培养液中供给锌过多或过少都不利于盐藻细胞的生长与物质积累。以培养基中6 mg/L的锌浓度对盐藻细胞生长、蛋白质合成与β-胡萝卜素积累的促进作用最大。这一锌浓度可用于盐藻的生产性培养。当培养液中锌浓度较高(8 mg/L)或较低(2 mg/L)时,单个盐藻细胞中的蛋白质与β-胡萝卜素含量较高。但此时,因培养液中细胞密度较低,盐藻细胞积累的物质总量仍然较少。在锌浓度较高或较低的逆境条件下,盐藻可能通过适应性反应形成了逆境蛋白质与胡萝卜素等。     

Changes in Lipid Metabolism during Adaptation of the Dunaliella salina Photosynthetic Apparatus to High CO2 Concentration

The effects of CO₂ on the content and composition of lipid fatty acids (FA) and on the photosynthetic characteristics of unicellular halophilic green alga Dunaliella salina (known to be susceptible to CO₂ stress) were investigated. It was shown that even one-day-long increase in the CO₂ concentration (from 2 to 10%) provoked an increase in the total amount of FA on the dry weight basis by 30%. After 7-day-long growth at 10% CO₂, this value was 2.7-fold higher than that at 2% CO₂. The difference in the FA content and composition indicated the activation of FA synthesis de novo and inhibition of their elongation and desaturation, as well as the increase in the relative content of saturated FA at 10% CO₂. It was demonstrated that, after one-day-long CO₂ stress, the MGDG/DGDG ratio increased fourfold without change in the sum of their FA, which indicates the increase in the proportion of lipids predisposed to micellar (hexagonal phase) but not lamellar structure formation. Under short-term CO₂ stress, the ratio of 3/6 FA increased and the content of E-16:113 FA in phosphatidylglycerols increased sharply. The drop in protein content especially in the photosystem I (PSI) preparations, as well as diminishing the ratio of F ₇₀₀-to-F ₆₈₆ nm fluorescence (F ₇₀₀/F ₆₈₆) under short-term CO₂ stress argued for the significant damage to PSI. The reversibility of these changes at more prolonged treatment (7 and 10 days) demonstrated that D. salina cells could restore the functional activity of PSI. The lower level of F ₇₀₀/F ₆₈₆, chlorophyll a (Chla)/Chlb, and 3/6 FA ratio in line with the higher level of E-16:113 in the cells growing for a long time at the high CO₂ concentration is characteristic for the new structural and functional state of the photosynthetic apparatus providing for the effective photosynthesis of D. salina under these conditions.     

Characterization of a 160 kD Photosystem II reaction center complex isolated from photoinhibited Dunaliella salina thylakoids

Photoinhibition in the green alga Dunaliella salina is accompanied by the formation of inactive Photosystem II reaction centers. In SDS-PAGE analysis, the latter appear as 160 kD complexes. These complexes are structurally stable, enough to withstand re-electrophoresis of excised gel slices from the 160 kD region. Western blot analyses with specific polyclonal antibodies raised against the D1 or D2 reaction center proteins provided evidence for the presence of both of these polypeptides in the re-electrophoresed 160 kD complex. Incubation of excised gel slices from the 160 kD region, under aerobic conditions at 4°C for a prolonged period of time, caused a break-up of the 160 kD complex into a 52 kD D1-containing and 80 and 26 kD D2-containing pieces. Western blot analysis with polyclonal antibodies raised against the apoproteins of CPI (reaction center proteins of PS I) did not show cross-reaction either with the 160 kD complex or with the 52, 80 and 26 kD pieces. The results show the presence of both D1 and D2 in the 160 kD complex and strengthen the notion of a higher molecular weight D1- and D2-containing complex that forms upon disassembly of photodamaged PS II units.Abbreviations Chl chlorophyll - PS II Photosystem II - D1 the 32 kD reaction center protein of PS II, encoded by the chloroplast psbA gene - D2 the 34 kD reaction center protein of PS II, encoded by the chloroplast psbD gene - CPI the 82 and 83 kD reaction center proteins of PS I, encoded by the chloroplast psaA and psaB genes - HL high light - LL low light This publication is dedicated to the memory of the late Professor Daniel Arnon, whom the first author will fondly remember for his many accounts of past scientific discovery and debate.     

杜氏盐藻渗透调节过程中的甘油代谢途径

杜氏盐藻在适应外界盐浓度变化的过程中,甘油是其主要的渗透调节物质。低渗处理提高藻细胞的呼吸速率６０％以上;高渗处理对呼吸无明显影响,但大大刺激光合放氧速率。呼吸链的细胞色素电子传递链抑制剂ＫＣＮ和交替氧化酶抑制剂ＳＨＡＭ对杜氏藻渗透调节过程中的呼吸．胞内甘油、ＡＴＰ、淀粉会量的变化有不同的抑制效果。低渗情况下,胞内甘油转化为淀粉,所需能量由正常呼吸链和交替氧化酶途径同时提供;高渗情况下．淀粉则降解为甘油,光下甘油合成的能量主要由光合电子链提供,暗中则由正常呼吸链提供。     

Localization of glycollate dehydrogenase in Dunaliella salina

Glycollate dehydrogenase of the halotolerant green alga Dunaliella salina, isolated from a brine pond, was found associated with the membrane fraction which exhibited complete photosynthetic activity. Highest enzyme activity was found in cells grown in the presence of 5% NaCl. Any increase in NaCl concentration led to a decrease in specific enzyme activity.Abbreviations PSI(II) photosystem I(II)     

Changes in the Character of the Cell Wall in Growth ofBacillus megaterium Cultures

1. (1)
   Исследовалась кинетика образования протопяастов и освобождения C¹⁴ из клеток Bacillus megaterium, предварительно меченых C¹⁴ диаминопимеловой кислотой, под действием лмзоцима в фосфатной среде.     
   
   

静态荧光光谱法研究杜氏盐藻的生长规律

测量了杜氏盐藻不同生长期的静态荧光光谱,得出了杜氏盐藻生长规律曲线。通过与传统的分光光度计法和血球计数板法研究盐藻生长规律的比较发现,该方法反映的是活盐藻细胞浓度的变化情况,更能反映盐藻实际生长规律;不仅操作简便,灵敏度高,而且可以实现远距离非接触测量。     

Physiological responses of Dunaliella salina and Dunaliella tertiolecta to copper toxicity

Species differences in heavy metal tolerance were investigated by comparing the responses of Dunaliella tertiolecta and Dunaliella salina to elevated concentrations of CuCl2. Although both species showed reduced cell number ml(-1) of algal culture, D. salina was more affected by increase in CuCl2. This reflects higher sensitivity of D. salina to CuCl2 compared to D. tertiolecta. Total chlorophyll in terms of microg ml(-1) was higher in D. tertiolecta at all tested CuCl2 levels, but in terms of microg cell(-1) no significant difference was observed between the two species. Total carotenoids in microg cell(-1) increased with increase in CuCl2 in both species and it was about five times higher in D. salina at all CuCl2 concentrations. While both species showed significant increase in lipid peroxidation at elevated CuCl2, the malondialdehyde content of D. salina cells was about three times higher at most CuCl2 concentrations. Although ascorbate peroxidase (APX) activity increased with increase in CuCl2 levels in both species, higher activity was observed in D. tertiolecta at all tested CuCl2 concentrations. Cu content of D. salina cells was higher than D. tertiolecta which may be due to larger volume of D. salina cells. In conclusion, since hydroxyl radical (HO*) produced from H2O2 by Cu2+ (Haber-Weiss cycle) is involved in lipid peroxidation, higher ascorbate peroxidase activity in D. tertiolecta may partly account for lower sensitivity of this species to CuCl2 compared to D. salina.     

甘油对杜氏盐藻电击转化的影响

通过在HEPES电击缓冲液中添加不同浓度的甘油,讨论了甘油对电转前细胞存活率的影响;通过在盐藻培养基中添加不同浓度的甘油,讨论了甘油对盐藻细胞生长的影响;使用含有不同浓度甘油的HEPES缓冲液介导质粒载体转入盐藻细胞,比较了甘油对于转化率的影响。实验结果表明,在电击缓冲液中添加0.5mol/L甘油能有效提高细胞存活率,促进转化细胞恢复生长,从而获得最佳转化效果。因此,0.5mol/L甘油可作为杜氏盐藻电击转化过程中一种良好的稳渗剂。     

The Selectivity of Milking of Dunaliella salina

The process of the simultaneous production and extraction of carotenoids, milking, of Dunaliella salina was studied. We would like to know the selectivity of this process. Could all the carotenoids produced be extracted? And would it be possible to vary the profile of the produced carotenoids and, consequently, influence the type of carotenoids extracted? By using three different D. salina strains and three different stress conditions, we varied the profiles of the carotenoids produced. Between Dunaliella bardawil and D. salina 19/18, no remarkable differences were seen in the extraction profiles, although D. salina 19/18 seemed to be better extractable. D. salina 19/25 was not “milkable” at all. The milking process could only be called selective for secondary carotenoids in case gentle mixing was used. In aerated flat-panel photobioreactors, extraction was much better, but selectiveness decreased and also chlorophyll and primary carotenoids were extracted. This was possibly related to cell damage due to shear stress.     

Continuous production of carotenoids from Dunaliella salina

During the in situ extraction of β-carotene from Dunaliella salina, the causal relationship between carotenoid extraction and cell death indicated that cell growth and cell death should be at equilibrium for a continuous in situ extraction process. In a flat-panel photobioreactor that was operated as a turbidostat cell numbers of stressed cells were kept constant while attaining a continuous well-defined light-stress. In this way it was possible to study the balance between cell growth and cell death and determine whether both could be increased to reach higher volumetric productivities of carotenoids. In the two-phase system a volumetric productivity of 8.3 mg β-carotene L(RV)(-1)d(-1) was obtained. In situ extraction contributed only partly to this productivity. The major part came from net production of carotenoid-rich biomass, due to a high growth rate of the cells and subsequent dilution of the reactor. To reach equilibrium between cell growth and cell death, sparging rates of dodecane could have been increased. However, already at the applied sparging rate of 286 L(dod)L(RV)(-1)min(-1) emulsion formation of the dodecane in the aqueous phase appeared. In a turbidostat without in situ extraction a volumetric productivity of 13.5 mg β-caroteneL(RV)(-1)d(-1) was reached, solely based on the continuous production of carotenoid-rich biomass.     

盐藻蛋白质组的研究进展

盐藻是一种公认的能耐受高盐度的海藻,是研究植物高盐适应的模式生物.高通量的蛋白质组学为人们深入探讨盐藻的耐盐机制提供了强有力的工具.就蛋白质组及其主要技术、盐藻蛋白质组的研究概况和研究展望作一简要综述.     

Uptake and efflux of inorganic carbon in Dunaliella salina

The apparent photosynthetic K_m (CO₂) of air-grown Dunaliella salina is 2 M as measured both by the filtering centrifugation technique and by O₂ electrode. These cells are capable of accumulating inorganic carbon (C_inorg) up to 20 times its concentration in the medium. It is suggested that air-grown Dunaliella cells are able to concentrate CO₂ within the cell. Analysis of the efflux of C_inorg from cells previously loaded with H¹⁴CO ₃ ^- demonstrated the existence of an internal pool which has an half-time of depletion of 2.5–7 min depending on the conditions of the experiment. This finding indicates that the internal C_inorg pool is not readily exchangeable with the external medium. Furthermore, the influence of the presence or absence of unlabelled C_inorg in the medium during the efflux experiment on the half-time observed indicate that efflux of C_inorg is not a simple diffusion process but is rather carrier-mediated.Abbreviation C_inorg inorganic carbon     

Biochemical Changes in Cultures of Nectria galligena during the Autolytic Phase of Growth

Some biochemical changes occurring in cultures of Nectria galligenaduring its autolytic phase of growth have been investigated.In nitrate-grown and autolysed cultures of this fungus the degreeof autolysis amounted to 57 per cent. The amount of myceliallipids decreased continuously with the age of the culture. Totalmycelial nitrogen did not substantially change within the first50 days of autolysis. The constancy in the amount of bound aminoacids released from mycelium of Nectria galligena strongly suggeststhat mycelial protein are not affected by autolysis.