Studies on the Microstructure and Ultrastructure of Photosynthetic Apparatuses in Azolla

The structures of photosynthetic apparatuses such as leaves, chloroplasts and symbiotic cyanobacterum (blue-green algae) in Azolla-Anabaena azollae associations (Azolla imbricata (Roxb) Nakai) which occur in paddy fields of China were examined using light, scanning and transmission electrn microscopy. Some comparisons were made with A. filiculoides, A. japonica, A. caroliniana, A. pinnata and A. mexicana. Cross sections of A. imbricata were observed by light microscopy and the symbiotic association between the eukaryotic water fern and its prokaryotic blue-green algal symbiont, an Anabaena, was studied. The symbiotic cyanobacterum cells occur not only in a mature leaf cavity, but also in early stages of leaf development, around leaf primordia, and even in macrospores. Under scanning electron microscopy (SEM) it is possible to see stomata and nipples on the surface of dorsal lobes of the fern. The species in the subgenus Euazolla (i.e.A. filiculoides, A. japonica, A. caroliniana and A. mexicana) have rounded nipples, but those in the subgenus Rizosperma (i.e.A. imbricata and A. pinnta) prolate ones. This morphological character is first reported to be related to the taxonomic system. The result of the observation with transmission electron microscopy (TEM) shows that A. filiculoides contains more thylakoides in chloroplasts than A. imbricata does, and the grana lamellae have more stacks in the former than in the latter. The differences are in agreement with the differentiation of the two species in photosynthetic capacity. This may be one of the differences between the two subgenera. The ultrastructures of the symbiotic cyanobacterum are similar to those of free-living Anabaena. The vegetative cells show a typical bilayered cell wall and the heterocysts have a thikened wall. The thylakoid membranes in both heterocysts and vegetative cells are oftenseen forming whirls. During the division of vegetative cells, their contents aggregate and then redistribute.     

聚球藻7942高效泌氨突变种的获得及其泌氨、谷氨酰胺合成酶活性、光合和生长

将含有Ａｎａｂａｅｎａｓｐ．ＰＣＣ７１２０反义ｇｌｎＡ基因片段的穿梭表达质粒ｐＤＣ－ＡＴＧＳ转化单细胞蓝藻聚球藻Ｓｙｎｅ－ｃｈｏｃｏｃｃｕｓ　ｓｐ．ＰＣＣ７９４２,通过同源重组,外源ＤＮＡ定位整合到染色体上。经过抗菌素筛选,获得一种高效泌氨的Ｓｙｎｅｃhｏｃｏｃｃｕｓ　ｓｐ．７９４２突变种。将此突变种固定化在聚氨脂泡沫中后,定量测定其谷氨酰胺合成酶（ＧＳ）活性。结果表明,固定化后的突变藻培养９ｄ后泌氨活性比自由生活的野生藻高１５６倍,ＧＳ活性降低７３．６％;其生长速度与同条件下野生藻相近,７７Ｋ荧光光谱表明突变种固定化后光系统Ⅱ活性提高４４％。     

仙鹤藓属(Atrichum)藓类植物组织培养再生体系的建立

报道了仙鹤藓(Atrichum undulatum(Hedw.)P.Beauv.)和仙鹤藓小形变种(Atrichum undulatum var.minus(Hedw.)Par.)的组织培养再生体系的建立.为研究仙鹤藓属(Atrichum)藓类愈伤组织的诱导和再分化,将仙鹤鲜和仙鹤藓小形变种原丝体接种在含有4%葡萄糖和0.2～2.0 mg/L 6-BA的MS培养基上,培养一个月后,成功地诱导出疏松、易碎的绿色愈伤组织.愈伤组织诱导和常规继代培养较适合的培养基为含4%葡萄糖和1～2 mg/L6-BA的MS培养基.当将继代培养5次的脱分化藓类愈伤组织转移到含4%葡萄糖但无任何激素的MS培养基上时,能再分化形成原丝体,而在无任何碳源的Benecke培养基上培养时,能再分化形成经原丝体阶段发育来的直立配子体.     

Effects of Cucumber Mosaic Virus Infection on Photosynthetic Activities of Tobacco Leaves and Chloroplasts

Changes in photosynthetic activities were studied with tobacco (Nicotiana tabacum L.) leaves and chloroplasts infected by cucumber mosaic virus (CMV) at the top, middle and bottom located leaves. Net photosynthetic rate was reduced at all three positioned leaves, with the maximum reduction occurring at the top leaves (31.9% of control). The infected chloroplasts showed a reduction in electron transport rates of the whole chain electron transport, photosystem Ⅱ (PSⅡ) and photosystem Ⅰ (PSⅠ). Since the decline in the whole chain electron transport (15.6% of control, H2O→MV) closely paralleled the decline in PSⅡ activity (20.9% of control, H2O→PBQ), the inhibition of the latter was probably responsible for the overall decrease. Chlorophyll a fluorescence measurements showed a variable reduced fluorescence yield (Fv/Fo) which indicated that PSⅡ was impaired and the CO2 assimilation was disturbed by CMV infection. Fluorescence emission spectra at 77 K indicated that energy distribution between PSⅡ and PSⅠ was affected. F686/F734 of infected leaves and chloroplasts increased and the greatest increase (331.1% of control ) was found in the top leaves. These data may conclude that the infection inhibited mainly the PSⅡ activity.     

蓝藻与植物叶绿体光合系统基因的生物信息学研究

用BLAST法比较了蓝藻和叶绿体中编码光合系统蛋白的基因碱基序列的同源性,其中蓝藻来自集胞藻6803和念珠藻7120,叶绿体来自地钱、烟草、水稻、裸藻、黑松、玉米、紫菜、拟南芥等。以集胞藻6803的碱基序列为基准(100％),与其他物种进行同源性比较。在光系统Ⅰ基因中,psaC同源性最高(90．14％),最低的是psaJ,(52．24％)。光系统Ⅱ基因中,同源性最高的是psbD基因(83．7l％),最低的是psbN(49．70%)。ATP合成酶基因中,同源性最高的是atpB基因(79．58％,),最低的是atpF(26．69％)。细胞色素b6／f复合物基因中,同源性最高的是petB(81．66％),最低的是petA(55．27％)。这些数据可为叶绿体的起源和进化提供一些证据。     

Homologous comparisons of photosynthetic system I genes among cyanobacteria and chloroplasts

It has now believed that chloroplasts arose from cyanobacteria, however, during endosymbiosis, the photosynthetic genes in chloroplasts have been reduced. How these changes occurred during plant evolution was the focus of the present study. Beginning with photosystem I (PSI) genes, a homologous comparison of amino acid sequences of 18 subunits of PSI from 10 species of cyanobacteria, chloroplasts in 12 species of eucaryotic algae, and 28 species of plants (including bryophytes, pteridophytes, gymnospermae, dicotyledon and monocotyledon) was undertaken. The data showed that 18 genes of PSI can be divided into two groups: Part I including seven genes ( psaA , psaB , psaC , psaI , psaJ , ycf3 and ycf4 ) shared both by cyanobacteria and plant chloroplasts; Part II containing another 11 genes ( psaD , psaE , psaF , psaK , psaL , psaM , btpA , ycf3 7, psaG , psaH and psaN ) appeared to have diversified in different plant groups. Among Part I genes, psaC , psaA and psaB had higher homology in all species of cyanobacteria and chloroplasts. Among Part II genes, only psaG , psaH and psaN emerged in seed plants.     

通过同源重组在聚球藻7002中表达小鼠金属硫蛋白-Ⅰ的初步研究

用PCR方法从海洋单细胞蓝藻聚球藻7002（Synechococcus sp. PCC 7002）基因组DNA中扩增得到藻蓝蛋白β亚基基因（cpcβ）的上游序列（Pcpcβ）,及编码谷氨酰胺合成酶的glnA基因片段．以Pcpcβ作为启动子、以glnA基因片段作为整合平台,构建含有小鼠金属硫蛋白-Ⅰ（mMT-Ⅰ）cDNA的同源整合表达载体pKGC-MT.通过自然转化法将整合表达载体导入聚球藻7002中,经氨苄青霉素筛选,得到遗传性状稳定的转基因藻.PCR检测证明mMT-Ⅰ基因已整合到蓝藻基因组DNA上;蛋白质印迹表明mMT-Ⅰ已在蓝藻中表达;ELISA结果显示mMT-Ⅰ在蓝藻中的表达量约为800 μg/g.     

TheAzolla-Anabaena association: Historical perspective,symbiosis and energy metabolism

The heterosporous water-fern genusAzolla is one of the few symbioses with a cyanobacterium in the genusAnabaena. TheAzolla-Anabaena association includes six extant speciesof Azolla, which are widely distributed in relatively placid tropical and/or temperate freshwater environments. The earliest mention of the plant seems to be in an ancient Chinese dictionary that appeared about 2000 years ago.Azolla was used in about the 11th century in Vietnam. By 1980 renewed interest in this symbiotic association was shown by the demand for a less fossil energy-dependent agricultural technology. The importation of a variety ofA. filiculoides may have been a most significant breakthrough for the improvementof Azolla cultivation in China. The history of research may be divided into three periods and a new biotechnological stageof Azolla research has recently begun. Each mature dorsal leaf lobe has an ellipsoid cavity which containsAnabaena azollae throughout its development. HeterocystousA. azollae from sixAzolla species share identical and highly specific antigens.Azolla and its endophyte exhibit a coordinated pattern of differentiation and development. Epidermal hair cells of the host are probably interactive with the symbiont. The interior surface of a mature leaf cavity is lined with an envelope and covered by a mucilaginous layer.A. azollae shares the cavity with small populations of the bacteriaPseudomonas andAzotobacter. Endophyte-freeAzolla may rarely occur in nature and can be generated by aseptic techniques.Anabaena azollae can be isolated fromAzolla fronds by gentle pressure and by enzymatic digestion. The free living cultures derived from theAnabaena so obtained differ in some respects, however, from the freshly extracted symbiont, and might better be called the presumptive isolate. BothAzolla andAnabaena contain specific photosynthetic pigments. The optimum conditions for photosynthesis have been measured.Azolla is a C₃ plant and has high net photosynthesis. PSII activity in the symbiont is low. Nitrogenase is localized in the heterocysts of the symbiont and has some advantages compared with free-living cyanobacteria. SymbioticA. azollae has a high frequency of heterocysts. Unidirectional hydrogenase occurs in the symbiont and recycles electrons and ATP. Simultaneous measurements of N₂ fixation and photosynthesis show the dependence of nitrogenase on photosynthetically captured radiation for energy by an indirect dependence on CO₂ fixation. The host contains most of the total GS and GDH activities, and the symbiont excretes a substantial portion of its newly fixed nitrogen as ammonium. The two partners in the association exhibit a comparable developmental gradient and a mechanism of cooperative integration for their energy metabolism, thus improving the efficiency of solar energy conversion and presenting a unique model for biotechnology.     

Construction and application of easy-to-detect cyanobacteria with vp28 gene

Journal of Applied Phycology - White Spot Syndrome Virus (WSSV) is the most harmful and pathogenic infectious agent in shrimp aquaculture. Vp28, a protein used to protect hosts against this virus,...