钙对蓝藻固氮受氯化钠胁迫的缓解效应及其与生理条件的关系

氯化钠胁迫导致蓝藻固氮活性的下降,可因加人适当浓度的氯化钠而有一定程度的缓解．在光合作用受抑（暗处理或添加光合抑制剂）、厌氧（Ａｒ或Ｎ２中）和有分子氧的情况下,此种缓解作用减弱．光合作用、需氧代谢（通气）和羟化反应（同时供给氢和氧）正常进行以及碳架（添加外源蔗糖或提高ＣＯ２浓度）供应良好时,钙对氯化钠胁迫的缓解效应增大．改善合成固氮酶的物质基础供应（同时供应ＣＯ２和Ｎ２）对此也有一定的正效应．     

分子氢在鱼腥蓝藻Anabaena 7120固氮活性受氧损伤中的保护作用

分子氢在一定程度上可以消除氧对蓝藻固氮活性的损伤而起一种保护作用。氧对蓝藻固氮活性的损伤主要在固氮反应初期,且是不可逆的。分子氢的保护作用也在反应初期,分子氢过迟加入,其保护作用就会受到削弱或消失,其最大保护作用是在与氧同时加入之时。分子氢的保护作用和生理条件有一定联系。年老的蓝藻中,分子氢支持的固氮活性对氧敏感小些。温度、CO_2、氮气和一系列抑制剂都只影响固氮活性的高低,并不改变分子氢的有益行为。蓝藻经乙炔预处理导致氢酶受抑时,分子氢对固氮活性受氧损伤时的保护作用即受到削弱或消失。     

短期高温伤害蓝藻Anabaena7120的固氮活性恢复与生理条件的关系

蓝藻经短期高温处理后,其固氮活性显著下降,但在合宜条件下,这种受伤害的固氮活性可以有一定程度的恢复。光下不仅比暗中恢复快,而且活性也高得多。光合抑制剂和外源碳水化合物分别减缓和促进受高温伤害的蓝藻固氮活性恢复。在光、暗和供给外源碳水化合物的条件下,厌氧(氩和氮中)对受高温伤害的蓝藻固氮活性恢复不利。与正常蓝藻有异的是,H_2,CO_2及H_2与O_2,CO_2与N_2的加合都阻碍受高温伤害的蓝藻固氮活性的恢复。     

蓝藻Anabaena7120断裂丝状体的固氮作用

蓝藻Anabaena 7120经甲苯处理后,其固氮活性不仅下降,而且对氧也很敏感。处理前24小时(?)时供给CO_2和N_2,其固氮活性受到促进,促进程度比单供给CO_2的大。氢对其支持和氢对其受氧损伤时的保护作用、光合抑制剂和暗处理对其抑制程度均比未经甲苯处理的蓝藻大。外源碳水化合物对其固氮活性也有促进,但同时加抑制剂时,碳水化合物的良好效应消失。     

甘露醇对氯化钠胁迫下蓝藻Anabaena 7120固氮活性的增强效应

营养液中添加外源的甘露醇后,蓝藻Ａｎａｂａｅｎａ ７１２０固氮受ＮａＣｌ胁迫的程度减弱。在光合作用不能进行或受到削弱,能量供应受阻、厌氧环境中和分子氧条件下,甘露醇的良好作用减小或消失。改善能涛和碳架供应,增强氢的利用或满足合成固氮酶蛋白所需物质需求时,甘露醇缓解ＮａＣｌ胁迫蓝藻固氮的程度明显增大。     

蓝藻Anabaena 7120光漂白细胞固氮的研究

蓝藻Anabaena 7120经光漂白后固氮活性明显下降,转入正常光照下又恢复活性。此种经光漂白的蓝藻细胞,其固氮活性对氧敏感度小,受分子氢的促进大些,而忍受CO_2和N_2抑制的浓度相对高些。其固氮活性为弱光和光合抑制剂减弱,而加入外源的碳水化合物则能提高它的固氮活性。当碳水化合物和光合抑制剂一起加入反应系统时,蓝藻光漂白细胞的固氮活性并不能受到促进。     

蓝藻Anabaena7120的固氮活力及其和光合作用的关系

蓝藻Anabaena 7120经用Ar+CO_2、空气和Ar处理后,固氮活性有明显不同。Ar+CO_2处理的活性比空气处理的高出数倍,而Ar处理的则比空气中的低很多。以上三种处理的Anabaena 7120固氮对不同生理条件反应不一样,固氮活性高者对CO和O_2的敏感程度小些、受到CO_2和N_2的抑制程度也轻。但是分子氢对三者固氮作用的支持效用相同,并且也是和氢酶活动有联系。弱光下固氮活力低的蓝藻固氮活性下降得更大些。光合抑制剂和结合态氮对固氮活力高的蓝藻固氮活性的抑制显著比固氮活力低者小。三者的放氢和放氧能力也不同,固氮活力高者放氧高而放氢量小些,低固氮活力的蓝藻正好相反。     

蓝藻Anabaena 7120的固氮放氢和同化力之间的关系

分子氮和二氧化碳对蓝藻Anabaena 7120固氮的抑制作用可因反应系统中pH值的提高以及对蓝藻进行预照光处理而削弱或消除。分子氢对经预照光处理的蓝藻固氮活性不但不支持,且有削弱。预暗处理的效应恰好相反。蓝藻经低温(4℃)预处理后,分子氢对其固氮活性支持减弱,甚至抑制。蓝藻放氢对分子氢和同化力水平的反应规律在趋势上与固氮基本相同。     

硝酸钾缓解氯化钠胁迫蓝藻Anabaena 7120固氮的生理基础

营养液中添加适量ＫＮＯ３可在一定程度上缓解ＮａＣｌ对鱼腥藻固氮活性的抑制作用。暗处理或加光合抑制剂时,ＫＮＯ３对ＮａＣｌ胁迫的缓解作用便消失。供给外源蔗糖、提高ＣＯ２浓度、同时供给ＣＯ２和Ｎ２时,ＫＮＯ３对缓解ＮａＣｌ胁迫的作用则增高．同时供给Ｏ２和Ｈ２对ＫＮＯ３的缓解作用增高影响较小,而在厌氧（Ａｒ或Ｎ２中）或单加氧下,ＫＮＯ３的缓解效应则明显减弱或消失．     

渗透胁迫下蓝藻固氮的氧稳定性研究

在聚乙二醇（PEG）的影响下．蓝藻固氮活性下降,对氧的不稳定性增大。PEG浓度愈高,固氮活性及其对氧的稳定性愈小。暗处理、光合抑制剂、N2和厌氧环境加剧氧对受渗透胁迫蓝藻固氮酶活的抑制,而CO2、蔗糖、分子氢以及N2和CO2的加合则使之减轻。     

The Oxygen-Scavenging System Protecting Nitrogenase from Oxygen in Cells of Blue-Green Algae

There is a heat stable oxygen-scavenging system (OSS) associated with membrane which reduces oxygen endogenously in cells of blue-green algae. Addition of the OSS to cell suspension of heterocystous oxygen sensitive Anabaena mutant and non-heterocystous Pleetonema boryanum led to an increase in their nitrogenase activity by 10–100-fold higher than those under microaerobic condition and also could restore effectively their acetylene reduction activity at higher oxygen concentration since the oxygen presented was reduced effectively. The results suggest that the OSS possesses a function protecting nitrogenase from oxygen in cells. Furthermore, it was found that the efficiency of reducing oxygen of OSS from the Anabaena mutant and Plectonema was lower than those from Anabaena wild and Gloeocapsa in atm. oxygen level. This may be ralated with the susceptibility of nitrogen fixation to oxygen in the cells of Anabaena mutant and Plectonema. The present study firstly indicades the relationship between the heat stable OSS associated with membrane and the mechanism of protecting nitrogenase from oxygen in cells of blue-green algae. Activities of catalase, peroxidase and superoxide dismutase do not show obvious difference in cellfree extract of Anabaena wild and mutant. Methyl viologen can induce nitrogenase activity of Anabaena mutant by subverting a portion of electon flow to accelerate oxygen reduction.     

低温对氯化钠胁迫下蓝藻固氮活性的影响

低温加剧氯化钠对蓝藻固氮的抑制,营养液中氯化钠浓度增高时,抑制程度更甚.能源受限(暗处理和加抑制剂时的光合受抑,N_2和Ar的厌氧下呼吸代谢受阻)和氧下固氮酶受到伤害时,低温处理使氯化钠对蓝藻固氮的抑制进一步加剧.在能源和还原剂供应,合成固氨酶蛋白的物质基础(如CO_2和N_2的加合).光合作用正常进行的条件得到改善和保证,以及供应CO_2、外源蔗糖和氮氧加合时,低温加剧氯化钠对蓝藻固氮的抑制程度明显变小.     

Oxygen Sensitive Nitrogen-Fixing Mutants of Anabaena

Two Anabaena mutants having heterocysts but incapable of fixing molecular nitrogen in air have been isolated by using ultraviolet radiation or NTG mutagenesis. Their vegetative cells differentiated into heterocysts at a higher frequency than that of the wild type. The phenotype of the mutants is stable and a low frequence of spontaneous reversion was observed. Under microaerobic condition the mutants cells can express the genetic information which encodes nitrogenase synthesis and were capable of utilizing nitrogen for growth with a low acetylene reductiop activity. The level of nitrogenase activity was correlated reciprocally with the content of cell phycocyanin and the light intensity. Both synthesis and activity of the mutant nitrogenase were very sensitive than wild type to the oxygen in vive. Introduction of 1% O2 (v/v) into the gas phase inhibited evidently acetylene reduction. Exposure of the mutant suspension to 20% O2 (v/v) resulted in total and irreversible denaturation of nitrogenase. Withdrawing of O2 in gas phase, the nitrogenase was synthesized de nero; The synthesis process was repressed by chloramphenical or ammonia. The nitrogenase activity of mutant cells increased significantly either by nitrogen- starvating to decrease the phycocyanin content or by lowering the light intensity. Specifically, during the anaerobic induction by treating the mutants filaments with diehloromethylurea which prevents photosynthetic oxygen production, the specific activity of mutant nitrogcnase was equivalent nearly to that of wild type. The ability to reduce 2, 3, 5-triphenyltetrazolium was lower in heterocysts and vegetative cells of mutants than in that of wild type. The results suggest that the oxygen sensitivity of nitrogen fixation by heterocystous bluegreen algal mutants may be duc to the defect of some enzymic systems which might play a role in scavenging oxygen toxity, so that the process of nitrogen fixation is inhibited by the active oxygen produced by vegetative cells. The mechanism of protecting nitrogenase from oxygen damage in blue-green algae is discussed.     

几种固氮蓝藻的固氮酶活性及其某些特性

对三种固氮蓝藻:固氮鱼腥藻(水生686)、柱孢鱼腥藻和鱼腥藻7120的整细胞及无细胞抽提液的固氮酶活性,进行了比较研究。水生686的整细胞酶活虽然不低(51.9毫米乙烯峰高/光密度/30分),仅次于柱孢鱼腥藻,但其无细胞抽提液的酶活却最低。这可能与它含有大量藻胶有关。研究了Mn++、Fe++对蓝藻固氮酶的作用,以及测定其在不同酶浓度下的反应动力学表明:柱孢鱼腥藻中不存在象深红螺菌中所看到的那种激活因子。用甲苯-乙醇溶液处理藻细胞,对固氮酶作原位测定,探索了它的氧损伤及氧保护机理。       

Alteration of the Fe protein of nitrogenase by oxygen in the cyanobacterium Anabaena sp. strain CA.

Changes in protein composition were noted when heterocysts of Anabaena sp. strain CA were isolated from filaments grown in 1% CO2-99% N2 and subsequently exposed to oxygen. Immunospecific Western blot analysis showed that the Fe protein of nitrogenase is altered. In cells grown under microaerobic conditions, the Fe protein was found in a form with an apparent molecular weight of 30,000. Exposure to oxygen caused a shift in the migration of this polypeptide to a position corresponding to an apparent molecular weight of 31,500. This modification was reversible upon removal of oxygen from the culture. Chloramphenicol did not inhibit the alteration in either direction. Suppression by ammonium nitrate of the recovery of nitrogenase activity from the effects of oxygen did not prevent the alteration of the protein. Other inhibitors of nitrogenase activity, (metronidazole, carbonyl cyanide m-chlorophenylhydrazone, and phenazine methosulfate) were tested for their effect on Fe protein modification. Alteration of the Fe protein may relate to the protection of nitrogenase from the deleterious effects of oxygen.     

Nitrogen fixation by Anabaena cylindrica

Summary Blending Anabaena cylindrica cultures results in a loss of nitrogenase activity which is correlated with the breakage of the filaments at the junctions between heterocysts and vegetative cells. Oxygen inhibition of nitrogen fixation was significant only above atmospheric concentrations. Nitrogen-fixation activities in the dark were up to 50% of those observed in the light and were dependent on oxygen (10 to 20% was optimal). Nitrogenase activity was lost in about 3 h when cells were incubated aerobically in the dark. Re-exposure to light resulted in recovery of nitrogenase activity within 2 h. Blending, oxygen, or dark pre-incubation had similar effects upon cultures grown under air or nitrogen and did not inhibit light-dependent CO₂ fixation. We conclude that heterocysts are the sites of nitrogenase activity and propose a model for nitrogen fixation by Anabaena cylindrica.     

Nitrogen Fixation by Thermophilic Blue-Green Algae (Cyanobacteria): Temperature Characteristics and Potential Use in Biophotolysis

Thermophilic, nitrogen-fixing, blue-green algae (cyanobacteria) were investigated for use in biophotolysis. Three strains of Mastigocladus laminosus were tested and were found to be equally effective in biophotolysis as judged by nitrogenase activity. The alga, M. laminosus NZ-86-m, which was chosen for further study, grew well in the temperature range from 35 to 50°C, with optimum growth at 45°C, at which temperature acetylene reduction activity was also greatest. The maximum tolerable temperature was 55°C. Acetylene reduction activity was saturated at a light intensity of 1 × 10⁴ ergs cm⁻² s⁻¹. Atmospheric oxygen tension was found to be slightly inhibitory to acetylene reduction of both slowly growing and exponentially growing cultures. Nonsterile continuous cultures, which were conducted to test problems of culture maintenance, could be operated for 2 months without any significant decrease in nitrogenase activity or contamination by other algae. Nitrogen-starved cultures of M. laminosus NZ-86-m produced hydrogen at comparable rates to Anabaena cylindrica. The conversion efficiency of light to hydrogen energy at maximum rates of hydrogen production was 2.7%.     

Oxygen inactivation and recovery of nitrogenase activity in cyanobacteria.

Exposure of nitrogen-fixing cultures of Anabaena spp. to 100% oxygen resulted in the rapid decline of nitrogenase activity. When oxygen-treated cells were transferred to 100% argon, nitrogenase activity was quickly restored in a process that required protein synthesis. Anaerobiosis was not essential for the recovery process; in fact, cells of Anabaena sp. strains CA and 1F will recover nitrogenase activity after prolonged incubation in 100% oxygen. Oxygen treatment acted directly on the intracellular nitrogenase and did not affect other metabolic processes. Examination of crude extracts of oxygen-treated Anabaena sp. strain CA indicated that both components of nitrogenase are inactivated. However, several lines of evidence suggest that oxygen treatment does not result in irreversible denaturation of nitrogenase, but rather results in a reversible inactivation which may serve as a protection mechanism. Nitrogenase present in crude extracts from cells of Anabaena sp. strain 1F which had been incubated for a prolonged period in 100% oxygen was less sensitive to oxygen in vitro than was nitrogenase of a crude extract of untreated cells.