谷胱甘肽对渗透胁迫下蓝藻固氮的增强效应

外源谷胱甘肽可在一定程度上缓和渗透脱水剂聚乙二醇对蓝藻固氮活性的胁迫。能源供应受抑（添加光合抑制剂和暗处理）、厌氧环境（Ar或N2中）和分子氧下，谷胱甘肽的此种良好效应减弱，而改善能量（正常光照下）和合成固氮酶蛋白所需物质（提高反应系统中CO2浓度，CO2和N2及H2和O2的加合，添加外源蔗糖）的供应时，谷胱甘肽对蓝藻固氮活性受聚乙二醇胁迫的缓和效应明显增强。     

甘露醇对蓝藻Anabaena7120固氮氧稳定性的增强效应

甘露醇可在一定程度上增加蓝藻固氮对氧的稳定性，高氧分压下，甘露醇的此种效应相对大一些。光合作用或有氧代谢不能进行（暗或Ar中），或光合受抑（添加抑制剂）时，甘露醇的有益作用减弱或消失。加强H2对固氮的支持（同时供给H2和O2），保证还原剂库或氯代谢的碳架供应（提高CO2浓度，同时供应CO2和N2）的条件下，甘露醇的良好效应明显增大。外源蔗糖对甘露醇增强蓝藻固氮氧稳定性没有显著的促进效用。     

CO2对NaCl胁迫下蓝藻固氮的影响

培养系统中CO2浓度增高时,蓝藻的固氮活性成倍增长,NaCl对固氮的胁迫明显减弱。能量供应受限（添加ATP形成抑制剂或暗处理）、厌氧环境（Ar或N2中）和在分子氧下,CO2的有益作用减弱或消失,反之或改善合成固氨酶蛋白所需物质的供应（CO2和N2以及地和O2的加合）时则有促进。在CO2浓度提高的情况下,外源蔗糖对NaCI胁迫蓝藻固氮无明显的缓解效应。     

低温对渗透胁迫下蓝藻固氮的影响

蓝藻经低温（0～4℃）预处理后，其在渗压脱水剂聚乙二醇（PEG）胁迫下的固氮活性下降进一步加剧。能源供应受限（光强减弱、暗处理）、厌氧（Ar或N2中）环境和分子氧下，下降程度更烈，而改善能源和还原剂以及合成固氮酶蛋白所需的物质供应（提高CO2浓度、CO2和N2以及H2和O2的加合、添加外源蔗糖）时即明显有所缓和。     

外源谷胱甘肽对氯化钠胁迫下蓝藻固氮活性的影响

外源谷胱甘肽（GSH）可在一定程度上削弱氯化钠对蓝藻固氮的抑制、能源受限（加抑制剂和暗处理,N2和Ar的厌氧下呼吸代谢受阻）和氧下固氮酶受到伤害时,谷胱甘肽的有益作用变小或消失,而在能源、还原剂、碳架和合成固氮酶蛋白的物质供应（正常光照、提高CO2浓度、添加外源蔗糖,同时供应CO2和N2以及H2和O2）得到改善和保证的条件下,则明显增大。     

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。     

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。     

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．     

Na2CO3胁迫下星星草幼苗叶绿体GST活性变化及其与相关指标的关系

通过对不同浓度Na2CO3胁迫下星星草幼苗培养基质和叶片渗透势、叶片相对电导率、叶绿体谷胱甘肽转移酶（GST）活性和O2^-产生速率的研究,以探讨星星草幼苗叶绿体GST活性在Na2CO3胁迫下的变化规律及其在抗Na2CO3胁迫中的作用。结果表明,在0～0．4％Na2CO3胁迫范围内,随着其浓度的增加星星草幼苗叶绿体GST活性增强,Na2CO3胁迫浓度继续增加则GST活性急剧减弱。星星草幼苗叶绿体GST活性随培养基质渗透势、叶片渗透势和叶片相对电导率以及叶绿体O2产生速率的变化趋势相似。叶绿体GST活性和Na2CO3胁迫浓度以及叶片渗透势之间、叶绿体GST活性和O2^-产生速率以及叶片渗透势之间、叶绿体GST活性和培养基质渗透势以及叶片渗透势之间、叶绿体GST活性和O2^-产生速率以及叶片相对电导率之间相关关系显著。说明叶绿体GST在星星草幼苗抵抗低强度（浓度）Na2CO3胁迫中起着非常重要的作用。     

去除氯化钠胁迫后的蓝藻固氮去铵阻抑

蓝藻在去除NaCl胁迫后,其固氮活性可以恢复,几乎接近生长蓝藻的水平,铵阻抑效应也逐渐消失。光合受抑(弱光下和加抑制剂)或呼吸代谢受阻(厌氧下),以致能源供应受限以及有分子氯或氧的条件下,蓝藻固氮活性恢复和去铵阻抑速率减慢,而改善能源或还原剂供应、外源蔗糖、H_2、CO_2、CO_2+N_2和H_2+O_2等处理则对去铵阻抑有不同程度促进。     

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.     

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．     

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。     

The effects of acetaldehyde on nitrogenase, hydrogenase and photosynthesis in the cyanobacterium Anabaena cylindrica.

Acetaldehyde was shown to be an irreversible inhibitor of nitrogenase, hydrogenase, CO2 fixation and growth in the cyanobacterium Anabaena cylindrica, but had no effect on photosynthetic electron flow as measured by Methyl Viologen-dependent O2 uptake. The concentration-dependence of the inhibition of nitrogenase and hydrogenase activities was determined, and it was shown that acetaldehyde inhibition poses problems for anaerobic experiments in which the activities of these enzymes are measured in the presence of the frequently used glucose/glucose oxidase/catalase/ethanol O2 trap. It is suggested that acetaldehyde may find use as an inhibitor in experiments designed to separate electron flow through the photosystems from consequent fixation of CO2 and N2.     

Regulation of CO on heterocyst differentiation and nitrate uptake in the cyanobacterium Anabaena sp. PCC 7120

AIMS: The aim of the present investigation was to study the effects of different inorganic carbon and nitrogen sources on nitrate uptake and heterocyst differentiation in the culture of cyanobacterium Anabaena sp. PCC 7120. METHODS AND RESULTS: Anabaena was cultivated in media BG11 containing combined nitrogen and supplementary NaHCO3 or CO2. Cell growth, heterocyst differentiation, nitrate reductase (NR, EC 1.7.7.2), glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) and NO uptake were analysed. The cells cultivated in BG11(0) medium with aeration were taken as reference. Experimental results showed that the differentiation frequency of heterocysts when the cells were cultivated with elevated CO2 was higher than that of the cells grown with air or bicarbonate. Heterocysts appeared unexpectedly when CO2 was introduced into the medium containing nitrate. However, no heterocysts emerged when CO2 was added to medium containing NH or urea, or when NaHCO3 was supplied to the medium with nitrate. Both nitrate uptake rate and nitrate reduction enzyme activity were depressed by the supplement of CO2 to the culture. The activity of G6PDH was enhanced with the increase in heterocyst differentiation frequency. CONCLUSION: CO2 might compete with NO for energy and electrons in the uptake process and CO2 appears favoured. This led to a high intracellular C/N ratio and a relative N limitation. So the process of heterocyst differentiation was activated to supplement nitrogen uptake. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provided an attractive possibility to form more heterocysts by rapid growth of Anabaena cells cultivated in the medium containing nitrate in order to increase nitrogen fixation and hydrogen production.     

Effects of long-term treatment with acetylene on nitrogen-fixing microorganisms.

Long periods of experimental incubation with acetylene led to a multifold enhancement of acetylene-reducing activity in Anabaena cylindrica, Anabaenopsis circularis, Rhodospirillum rubrum, and Azotobacter vinelandii. Rates of acetylene reduction showed a gradual increase and reached a peak after 2 to 6 h of continuous incubation under acetylene. Thereafter, enzyme activity rapidly declined. A similar enhancement of ethylene production was observed when pretreatment with acetylene was interrupted periodically by a brief exposure to ambient (or oxygen-free) atmosphere without acetylene although the decline of acetylene-reducing activity was less rapid. Pretreatment with acetylene depressed photosynthetic 14CO2 fixation and 15N2 incorporation in Anabaena cylindrica. It is concluded that assessments based on long-term experimental incubation with acetylene may grossly overestimate the actual quantities of fixed nitrogen in the field.     

Effects of long-term treatment with acetylene on nitrogen-fixing microorganisms.

Long periods of experimental incubation with acetylene led to a multifold enhancement of acetylene-reducing activity in Anabaena cylindrica, Anabaenopsis circularis, Rhodospirillum rubrum, and Azotobacter vinelandii. Rates of acetylene reduction showed a gradual increase and reached a peak after 2 to 6 h of continuous incubation under acetylene. Thereafter, enzyme activity rapidly declined. A similar enhancement of ethylene production was observed when pretreatment with acetylene was interrupted periodically by a brief exposure to ambient (or oxygen-free) atmosphere without acetylene although the decline of acetylene-reducing activity was less rapid. Pretreatment with acetylene depressed photosynthetic 14CO2 fixation and 15N2 incorporation in Anabaena cylindrica. It is concluded that assessments based on long-term experimental incubation with acetylene may grossly overestimate the actual quantities of fixed nitrogen in the field.