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41.
42.
The optimal temperature for the nitrogenase activity in the terrestrial cyanobacterium N. flagelliforme was 21–28℃; the optimal water content in thallus was 1000--1500%; the light saturation was between 150–200 J·m-2·s-1. The thallus of N. flagelliforme is extremely sensitive to higher temperature in wet. Long-term exposure of wetted thallus to high temperature at 45℃ causes rapid declination of its nitr0genase activity to zero. Under dry condition, N. flagelliforme is extremely resistant to extensive desiccation and heat exposure. Dry thalli exposed to 55℃, 5 hours daily for 21 days, show no marked change in its nitrogenase activity. The thalli preincubated in wet condition for 4–5 days, are highly sensitive against desication. However, repeated drying/wetting cycles induce a slow and gradual increase of its nitrogenase activity and improve the resistance of its nitrogenase activity against desiccation. High concentrated NaC1 salt solution (0.17–0.43 mol/L) depletes nitrogenase activity of the thalli quickly. Above result shows that N. flagelliforme is not able to resist against salt. The physiological characteristics of nitrogen fixation of cyanobacterium N. flagelliforme may be eonsidered as a result of drought adaptation of the terrestrial ecological condition aad the drying westting cycle is perhaps a necessary factor to maintain its growth. 相似文献
43.
The ultrastructure of the vegetative cells of Nostoc fiagelliforme Born. et Flah. was investigated with high pressure freezing and freeze substitution technique and compared with the results obtained by using conventional preparation methods. During the processes of chemical fixation, dehydration and embedding, the cell structures might be more artificially modified than that obtained from high pressure freezing and freeze substitution. With the present method, the sheath of N. fiageUiforme could be well-penetrated and no extra big space could exist between the cell and the sheath. The cell protoplasm rarely shrinked. Some fine structures of cell inclusions and unit membranes became visualized. Many bacteria were harbored in the sheath. In addition, the presence of big vacuoles in the cell of N. fiageUiforme as well as the presence of bacteria in the sheath shown in the present preparation for cyanobacteria has not been described so far in the literature. 相似文献
44.
采用DEAE阴离子交换层析和Sephadex G100凝胶层析对液体悬浮培养发状念珠藻胞外多糖进行纯化, 得到两个组分NFPS1和NFPS2。对组分NFPS2进行理化性质分析, 并与野生发状念珠藻多糖NFPS0的性质进行对比。结果表明二者具有相似的单糖组成, 均为葡萄糖、木糖、半乳糖、甘露糖; 表观分子量分别为2.79×105、2.26×105; 均不含核酸、蛋白质等物质, 是非硫酸化多糖; 有较高的热稳定性, 其降解温度在245oC左右。但在微观结构上, 两者存在一定差别。 相似文献
45.
A desiccation-tolerant cyanobacterium, Nostoc commune, showsunique responses to dehydration. These responses are: (i) lossof PSII activity in parallel with the loss of photosynthesis;(ii) loss of PSI activity; and (iii) dissipation of light energyabsorbed by pigment–protein complexes. In this study,the deactivation of PSII is shown to be important in avoidingphotoinhibition when the Calvin–Benson cycle is repressedby dehydration. Furthermore, our evidence suggests that dissipationof light energy absorbed by PSII blocks photoinhibition understrong light in dehydrated states. 相似文献
46.
Growth characteristics of the cyanobacterium Nostoc flagelliforme in photoautotrophic, mixotrophic and heterotrophic cultivation 总被引:1,自引:0,他引:1
Nostoc flagelliforme is a terrestrial cyanobacterium with high economic value. Dissociated cells separated from a natural colony of N. flagelliforme were cultivated for 7 days under either phototrophic, mixotrophic or heterotrophic culture conditions. The highest biomass,
1.67 g L−1 cell concentration, was obtained under mixotrophic culture, representing 4.98 and 2.28 times the biomass obtained in phototrophic
and heterotrophic cultures, respectively. The biomass in mixotrophic culture was not the sum as that in photoautotrophic and
heterotrophic cultures. During the first 4 days of culture, the cell concentration in mixotrophic culture was lower than the
sum of those in photoautotrophic and heterotrophic cultures. However, from the 5th day, the cell concentration in mixotrophic
culture surpassed the sum of those obtained from the other two trophic modes. Although the inhibitor of photosynthetic electron
transport DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] efficiently inhibited autotrophic growth of N. flagelliforme cells, under mixotrophic culture they could grow by using glucose. The addition of glucose changed the response of N.flagelliforme cells to light. The maximal photosynthetic rate, dark respiration rate and light compensation point in mixotrophic culture
were higher than those in photoautotrophic cultures. These results suggest that photoautotrophic (photosynthesis) and heterotrophic
(oxidative metabolism of glucose) growth interact in mixotrophic growth of N. flagelliforme cells. 相似文献
47.
Cytochemical changes in the developmental process of Nostoc sphaeroides (cyanobacterium) 总被引:1,自引:0,他引:1
There are several apparent developmental stages in the life cycle of Nostoc sphaeroides Kützing, an edible cyanobacterium found mainly in paddy fields in central China. The cytochemical changes in developmental
stages such as hormogonia, aseriate stage, filamentous stage and colony in N. sphaeroides were examined using fluorescent staining and colorimetric methods. The staining of acidic and sulfated polysaccharides increased
with development when hormogonia were used as the starting point. Acidic polysaccharides (AP) were most abundant at the aseriate
stage and then decreased, while the sulfated polysaccharides (SP) were highest at the colony stage. Quantitatively, along
the developmental process from hormogonia to colony, total carbohydrates first increased, then became stable, and then reached
their highest level at the colony stage, while reducing sugars were highest at the hormogonia stage and then decreased sharply
once development began. SP were not detectable in the hot water soluble polysaccharides (HWSP), and hormogonia had the lowest
content of AP, while old colonies had the highest. The AP content of the aseriate stage, filamentous stage and young colony
stage were very similar. The evolutionary relationships reflected in the developmental stages of N. sphaeroides are discussed. 相似文献
48.
We have studied the naturally split α subunit of the DNA polymerase III (DnaE) intein from Nostoc punctiforme PCC73102 (Npu) using purified proteins and determined an apparent first-order rate constant of (1.1±0.2)×10-2 s−1 at 37 °C. This represents the highest rate reported for the protein trans-splicing reaction so far (t1/2 of ∼ 60 s). Furthermore, the reaction was very robust and high-yielding with respect to different extein sequences, temperatures from 6 to 37 °C, and the presence of up to 6 M urea. Given these outstanding properties, the Npu DnaE intein appears to be the intein of choice for many applications in protein and cellular chemistry. 相似文献
49.
3种念珠藻多糖对自由基的清除作用 总被引:11,自引:1,他引:10
研究了地木耳(Nostoc commune)、葛仙米(N.sphaerohies)和发菜(N.flagelliforme)3种念珠藻多糖对自由基的清除作用。结果表明,3种念珠藻多糖对超氧阴离子自由基和羟自由基具有很强的清除作用,且呈量效关系,地木耳清除超氧自由基作用最强,最高清除率达72.3%,葛仙米和发菜分别为46.7%、35.5%;发菜清除羟自由基效果最强,最高清除率达74.3%,葛仙米和地木耳清除率分别为49.0%、46.7%;3种念珠藻多糖对DPPH自由基的清除作用不显著。 相似文献
50.
Effects of ammonium on the photosynthetic recovery of Nostoc flagelliforme Berk. et M. A. Curtis were assayed when being rehydrated in low‐K+ or high‐K+ medium. Its photosynthetic recovery was K+ limited after 3 years of dry storage. The potassium absorption of N. flagelliforme reached the maximum after 3 h rehydration in low‐K+ medium but at 5 min in high‐K+ medium. The K+ content of N. flagelliforme rehydrated in high‐K+ medium was much higher than that in low‐K+ medium. The maximal PSII quantum yield (Fv/Fm) value of N. flagelliforme decreased significantly when samples were rehydrated in low‐K+ medium treated with 5 mM NH4Cl. However, the treatment of 20 mM NH4Cl had little effect on its Fv/Fm value in high‐K+ medium. The relative Fv/Fm 24 h EC50 (concentration at which 50% inhibition occurred) value of NH4+ in high‐K+ medium (64.35 mM) was much higher than that in low‐K+ medium (22.17 mM). This finding indicated that high K+ could alleviate the inhibitory action of NH4+ upon the photosynthetic recovery of N. flagelliforme during rehydration. In the presence of 10 mM tetraethylammonium chloride (TEACl), the relative Fv/Fm 24 h EC50 value of NH4+ was increased to 46.34 and 70.78 mM, respectively, in low‐K+ and high‐K+ media. This observation suggested that NH4+ entered into N. flagelliforme cells via the K+ channel. Furthermore, NH4+ could decrease K+ absorption in high‐K+ medium. 相似文献