摘要：
The present work investigated the inorganic carbon (C-i) uptake, fluorescence quenching and photo-inhibition of the edible cyanobacterium Ge-Xian-Mi (Nostoc) to obtain an insight into the role of CO2 concentrating mechanism (CCM) operation in alleviating photo-inhibition. Ge-Xian-Mi used HCO3- in addition to CO2 for its photosynthesis and oxygen evolution was greater than the theoretical rates of CO2 production derived from uncatalysed dehydration of HCO3-. Multiple transporters for CO2 and HCO3- operated in air-grown Ge-Xian-Mi. Na+-dependent HCO3- transport was the primary mode of active C-i uptake and contributed 53-62% of net photosynthetic activity at 250 mumol L-1 KHCO3 and pH 8.0. However, the CO2-uptake systems and Na+-independent HCO3- transport played minor roles in Ge-Xian-Mi and supported, respectively, 39 and 8% of net photosynthetic activity. The steady-state fluorescence decreased and the photochemical quenching increased in response to the transport-mediated accumulation of intracellular C-i. Inorganic carbon transport was a major factor in facilitating quenching during the initial stage and the initial rate of fluorescence quenching in the presence of iodoacetamide, an inhibitor of CO2 fixation, was 88% of control. Both the initial rate and extent of fluorescence quenching increased with increasing external dissolved inorganic carbon (DIC) and saturated at higher than 200 mumol L-1 HCO3-. The operation of the CCM in Ge-Xian-Mi served as a means of diminishing photodynamic damage by dissipating excess light energy and higher external DIC in the range of 100-10000 mumol L-1 KHCO3 was associated with more severe photo-inhibition under strong irradiance.
摘要：
Effects of potassium on the photosynthetic recovery of Nostoc flagelliforme (Berk. & Curtis) Bornet & Flahault were investigated to determine its exact role during rehydration. Potassium enhanced recovery of the ability to reduce the primary quinone-type acceptor (Q(A)) and plastoquinone (PQ) pool and the area over the fluorescence rise curve was increased by 127%. The proportions of closed PSII reaction centers at phases J and I and the net rate of closure of PSII reaction centers were decreased by, respectively, 19%, 8%, and 23% with the addition of potassium, due to changes in the ability of PSII for multiple turnovers needed to reduce the PQ pool. Potassium significantly enhanced the probability of electron transfer beyond Q(A) and the recovery of electron transport flux per PSII reaction center. Electron transport from water to methyl viologen for samples rehydrated in K+-free BG(11) medium was 54% of those with the addition of potassium. However, electron flow from water to p-benzoquinone and from reduced 2,6-dichlorophenol-indophenol to methyl viologen showed little change with the addition of potassium. The fast phase and slow phase of millisecond delayed light emission and the ATP content for samples rehydrated in K+-free BG(11) medium were, respectively, 71.6%, 50.7%, and 77.1% of those with the addition of potassium. These suggested that potassium affected electron transfer from PQ to plastocyanin through the cytochrome b(6)f complex and the proton motive force across the thylakoid membranes, probably reflecting its role in charge balance during H+ transport by the cytochrome b(6)f complex.
作者机构：
[Qiu, BS] Cent China Normal Univ, Coll Life Sci, Wuhan 430079, Hubei, Peoples R China.;Nanjing Univ, Coll Life Sci, Nanjing 210093, Peoples R China.;Shantou Univ, Inst Marine Biol, Ctr Sci, Shantou 515063, Guangdong, Peoples R China.
通讯机构：
[Qiu, BS] C;Cent China Normal Univ, Coll Life Sci, Wuhan 430079, Hubei, Peoples R China.
摘要：
The photosynthetic response of Nostoc flagelliforme to desiccation and rehydration was investigated. The initial, variable and maximal chlorophyll fluorescence increased from the beginning of desiccation (fully hydrated), reached maxima at a water loss of about 35% and then decreased with further water loss. The area over the fluorescence induction curve reached a maximum at a water loss of about 70%. Pigment contents of chlorophyll a, phycocyanin and allophycocyanin were constant during the photosynthetic recovery phase following rehydration. A fast initial phase of recovery was completed within half an hour after rehydration, and further changes in 77 K fluorescence emission spectra were mainly related to the fluorescence level at 695 nm. A decrease in fluorescence intensities from phycobiliproteins was not detected from 0.5 to 24 h. The initial fluorescence was high at the beginning of rehydration and decreased sharply during photosynthetic recovery. This decrease appeared to be mainly related to the activation or repair of photosystem II (PS II) rather than changes in the coupling and assembly of phycobilisomes. The change of variable fluorescence and the PS II photochemical efficiency value (Fv/F m) correlated well with the recovery of PS II activity during rehydration. Nostoc flagelliforme required light and de novo protein synthesis to recover its photosynthetic activity fully during rehydration. In darkness, Fv/Fm, recovered 3.4% of activity in dried field samples but 18.9% of activity in samples dry for 2 days. When light was provided in the presence of chloramphenicol, Fv/Fm recovered 10.1% or 39.5% of activity in dried field samples and in samples dry for 2 days, respectively.
作者机构：
[Qiu, BS] Nanjing Univ, Coll Life Sci, Nanjing 210093, Jiangsu, Peoples R China.;Cent China Normal Univ, Coll Life Sci, Wuhan 4730079, Hubei, Peoples R China.
通讯机构：
[Qiu, BS] N;Nanjing Univ, Coll Life Sci, Nanjing 210093, Jiangsu, Peoples R China.
摘要：
The metabolism of reactive oxygen species in Nostoc flagelliforme and effects of exogenous oxidants on its photosynthetic recovery were investigated to obtain insight into oxidative stress in desiccation and its possible damaging impact on photosynthetic apparatus. No ascorbate was detected with ascorbate oxidase in N. flagelliforme. Superoxide dismutase (SOD) remained active even after three years drying storage and its activity was 78% of that in fully recovered samples. The SOD activity decreased during desiccation or in drying storage. Intracellular active oxygen production was studied by incubating samples in BG(11) medium for 2 h and measuring the oxidation of 2',7'-dichlorohydrofluorescein diacetate. The production rate was 38.11 nmol DCF g (d.wt)-1 h-1 in dried field samples and was significantly higher than in fully recovered or air-dried samples. The balance between intracellular active oxygen production and the defense systems might break down in air-dried and dried field samples. Treatment with exogenous oxidants slowed the photosynthetic recovery especially with singlet oxygen. Oxidative stress might play an important role in desiccationinduced damages to the photosynthetic apparatus.
摘要：
Diurnal photosynthesis of Nostoc flagelliforme was investigated at varied levels of CO2 concentrations and desiccation in order to estimate the effects of enriched CO2 and watering on its daily production. Photosynthetic activity was closely correlated with the desiccated status of the algal mats, increased immediately after watering, reached a maximum at moderate water loss, and then declined with further desiccation. Increased CO2 concentration enhanced the diurnal photosynthesis and raised the daily production. Watering twice per day enhanced the daily production due to prolonged period of active photosynthesis. The values of daily net production were 1321280 mumol CO2 g (d. wt)(-1) d(-1), corresponding to about 0.6-6.1% daily increase in dry weight. High-CO2-grown mats required higher levels of photon flux density to saturate the alga's photosynthesis in air. Air-grown mats showed higher photosynthetic affinity for CO2 and higher levels of dark respiration compared with high-CO2-grown samples.
期刊：
Journal of Applied Phycology,2002年14(5):423-429 ISSN：0921-8971
通讯作者：
Liu, ZL
作者机构：
[Liu, ZL] Nanjing Univ, Coll Life Sci, Jiangsu 210093, Peoples R China.;Cent China Normal Univ, Coll Life Sci, Wuhan 430079, Hubei, Peoples R China.
通讯机构：
[Liu, ZL] N;Nanjing Univ, Coll Life Sci, Jiangsu 210093, Peoples R China.
摘要：
Ge-Xian-Mi (an edible species of Nostoc) grows in some mountain paddy fields in China during winter and forms macroscopically visible subspherical colonies. The geology and climate at one of its locations, Hefeng County, were investigated, and the present-day situation of Ge-Xian-Mi was assessed in order to raise awareness that it may be endangered. There were formerly 796 ha of rice fields suited to its growth in Hefeng County and the maximum annual yield ever reached was 25 t. The annual mean temperature is about 12.2degreesC, and the annual rainfall is 1934 mm with mean relative humidity of 78-87%. The distribution of Ge-Xian-Mi was found to be associated with the source of water and the pH values of water suited to its growth were 6.2-6.3. Soils in its habitats were enriched with phosphorus and contained more microbes than those without its distribution. With changing agricultural techniques most of the habitats are endangered or already extinct. The widespread use of herbicides, pesticides and fertilizers containing chlorine had been suggested to be an important factor limiting its distribution. The taxonomic identity of Ge-Xian-Mi is discussed.
摘要：
Microcystis aeruginosa Kutz. 7820 was cultured at 350 and 700 muL.L-1 CO2 to assess the impacts of doubled atmospheric CO2 concentration on this bloom-forming cyanobacterium. Doubling Of CO2 concentration in the airflow enhanced its growth by 52%-77%, with pH values decreased and dissolved inorganic carbon (DIC) increased in the medium. Photosynthetic efficiencies and dark respiratory rates expressed per unit chl a tended to increase with the doubling of CO2. However, saturating irradiances for photosynthesis and light-saturated photosynthetic rates normalized to cell number tended to decrease with the increase of DIC in the medium. Doubling of CO2 concentration in the airflow had less effect on DIC-saturated photosynthetic rates and apparent photosynthetic affinities for DIC. In the exponential phase, CO2 and HCO3- levels in the medium were higher than those required to saturate photosynthesis. Cultures with surface aeration were DIC limited in the stationary phase. The rate of CO2 dissolution into the liquid increased proportionally when CO2 in air was raised from 350 to 700 muL.L-1, thus increasing the availability of DIC in the medium and enhancing the rate of photosynthesis. Doubled CO2 could enhance CO2 dissolution, lower pH values, and influence the ionization fractions of various DIC species even when the photosynthesis was not DIC limited. Consequently, HCO3- concentrations in cultures were significantly higher than in controls, and the photosynthetic energy cost for the operation of CO2 concentrating mechanism might decrease.
摘要：
Photosynthetic responses of rewetted Nostoc flagelliforme to CO2, desiccation, light and temperature were investigated under emersed conditions in order to characterize its ecophysiological behaviour in nature. Net photosynthesis increased to a maximum rate at about 30 % water loss, then decreased, while dark respiration always decreased with the progress of desiccation. Light-saturated photosynthesis and dark respiration were significantly reduced at 8°C, but remained little affected by changes of temperature within the range of 15-35°C. Photosynthetic efficiency (α) was maximal at the beginning of desiccation and then reduced with increased water loss. Saturating irradiance for photosynthesis was about 194-439 μmol quanta m-2 s-1, being maximal at about 30 % water loss. No photoinhibition was observed at irradiances up to 1140 μmol m-2 s-1. Light compensation points were about 41-93 μmol m-2 s-1. Photosynthesis of N. flagelliforme was CO2-limited at the present atmospheric CO2 level. The CO2-saturated photosynthesis increased with increase of irradiance (190-1140 μmol m-2 s-1) and temperature (8-25°C) and decreased significantly with water loss (0-75 %). Photosynthetic affinity for CO2 was sensitive to temperature and irradiance. The CO2 compensation point (Γ) increased significantly with increased temperature and was insensitive to irradiance. Desiccation did not affect F values before water loss exceeded 70 %. Photorespiratory CO2 release did not occur in N. flagelliforme at the current atmospheric CO2 level.
