硝酸盐供应水平对平邑甜茶幼苗生长、光合特性与15N吸收、利用的影响

以霍格兰营养液为培养基质,采用¹⁵N同位素示踪技术,研究不同浓度¹⁵NO₃^--N (0、2.5、5、10和20 mmol·L^-1,分别以N₀、N₁、N₂、N₃和N₄表示)对平邑甜茶幼苗生长、光合作用、¹⁵N吸收、利用及分配的影响.结果表明:与其他处理相比,N₂处理幼苗叶绿素含量、叶面积及各器官干质量最大.叶片净光合速率(P_n)随¹⁵NO₃^--N浓度的增加显著增大,但¹⁵NO₃^--N浓度超过N₂处理后P_n略有下降.处理20 d时,N₂处理幼苗根系活力最大,根系长度、根系总表面积和根尖数也显著高于其他处理.各处理间¹⁵N分配率差异显著,N₂处理幼苗各器官间¹⁵N分配率最均衡,¹⁵N利用率也较高;随¹⁵NO₃^--N浓度增加,各处理幼苗全氮量和¹⁵N吸收量呈先升高后降低的趋势,且在N₂处理时最大,分别为103.77和21.57 mg.处理12 d后,叶片硝酸还原酶(NR)活性以N₂处理最高,N₄处理最低,至第16天时,N₄处理较N₂处理降低了84.9%.因此,¹⁵NO₃^--N供应过低抑制幼苗光合作用及氮素吸收,¹⁵NO₃^--N供应过高则抑制幼苗体内硝态氮同化及根系生长,均不利于苹果幼苗生长及氮素营养吸收利用,适量供氮有利于苹果幼苗的生长、光合作用的提高,以及氮素的吸收、利用和分配.     

硝酸盐供应水平对平邑甜茶幼苗生长、光合特性与15N吸收、利用的影响

以霍格兰营养液为培养基质,采用¹⁵N同位素示踪技术,研究不同浓度¹⁵NO₃^--N (0、2.5、5、10和20 mmol·L^-1,分别以N₀、N₁、N₂、N₃和N₄表示)对平邑甜茶幼苗生长、光合作用、¹⁵N吸收、利用及分配的影响.结果表明:与其他处理相比,N₂处理幼苗叶绿素含量、叶面积及各器官干质量最大.叶片净光合速率(P_n)随¹⁵NO₃^--N浓度的增加显著增大,但¹⁵NO₃^--N浓度超过N₂处理后P_n略有下降.处理20 d时,N₂处理幼苗根系活力最大,根系长度、根系总表面积和根尖数也显著高于其他处理.各处理间¹⁵N分配率差异显著,N₂处理幼苗各器官间¹⁵N分配率最均衡,¹⁵N利用率也较高;随¹⁵NO₃^--N浓度增加,各处理幼苗全氮量和¹⁵N吸收量呈先升高后降低的趋势,且在N₂处理时最大,分别为103.77和21.57 mg.处理12 d后,叶片硝酸还原酶(NR)活性以N₂处理最高,N₄处理最低,至第16天时,N₄处理较N₂处理降低了84.9%.因此,¹⁵NO₃^--N供应过低抑制幼苗光合作用及氮素吸收,¹⁵NO₃^--N供应过高则抑制幼苗体内硝态氮同化及根系生长,均不利于苹果幼苗生长及氮素营养吸收利用,适量供氮有利于苹果幼苗的生长、光合作用的提高,以及氮素的吸收、利用和分配.     

利用15N示踪技术研究木荷与马尾松幼苗叶片对NO2的吸收与分配

大气氮氧化物(NO_x=NO+NO₂)随着干沉降进入森林生态系统时,会首先接触森林冠层。森林乔木能通过叶片吸收多少NO₂以及对吸收的NO₂是如何分配的,目前尚不清楚。该研究利用¹⁵N稳定同位素示踪技术,对中国南方常见乔木树种木荷(Schima superba)和马尾松(Pinus massoniana)幼苗在黑暗和光照两种条件下进行了¹⁵NO₂静态箱熏蒸实验,检测并分析了两种植物的¹⁵N回收率以及吸收的NO₂在植物各组织中的分配结果。结果显示:植物主要通过气孔吸收NO₂,木荷和马尾松在黑暗条件下整体分别能回收10.3%±5.9%和20.4%±7.0%¹⁵NO₂,在光照条件下整体分别能回收35.9%±5.4%和68.2%±7.6%¹⁵NO₂。两种植物各组织中的平均干质量¹⁵     

不同黄腐酸用量对‘红将军’苹果产量、品质和15N-尿素去向的影响

以15年生红将军/八棱海棠为试材,运用¹⁵N同位素示踪技术,设置单施尿素(CK)及尿素配施不同用量黄腐酸处理(黄腐酸用量分别为75、150、300和450 kg·hm^-2,分别以NF₁、NF₂、NF₃和NF₄表示),研究不同黄腐酸用量对苹果植株¹⁵N-尿素吸收、利用、残留、损失及果实产量和品质的影响.结果表明: 至果实成熟期,苹果根系、一年生枝和叶片的Ndff值(植株器官从肥料中吸收分配到的¹⁵N量对该器官全氮量的贡献率)均为NF₃>NF₄>NF₂>NF₁>CK,且各处理间差异显著.植株全氮量和¹⁵N吸收量均以NF₃处理最大,其次为NF₄处理,CK处理最低.与CK处理相比,NF₁、NF₂、NF₃和NF₄处理¹⁵N利用率分别提高了14.2%、33.5%、64.2%和50.0%,而¹⁵N损失率分别降低了9.1%、18.5%、37.1%和28.7%.不同处理土壤¹⁵N残留量不同.配施黄腐酸处理0～60 cm土层¹⁵N残留量显著高于CK处理,其中以NF₃处理最多,而在60～100 cm土层显著低于CK处理.NF₃处理单株产量和纯收益较CK处理增幅最大,分别为15.8%和20.2%,其次为NF₄处理,同时,NF₃处理果实硬度、可溶性固形物含量和糖酸比均达到最高水平.通过对果实产量和氮素利用率与黄腐酸施用量进行拟合分析,得出本试验条件下适宜的黄腐酸用量为326.41～350.61 kg·hm^-2.     

施肥深度对矮化苹果15N尿素吸收、利用及损失的影响

以5年生烟富3/M26/平邑甜茶为试材,采用¹⁵N同位素示踪技术,研究表层(0 cm)、上层(20 cm)和中层(40 cm)3个施肥深度对矮化苹果¹⁵N 尿素吸收、分配及利用特性的影响.结果表明： 20 cm施肥处理的叶面积、叶绿素含量和叶片全氮含量显著高于0和40 cm施肥处理.不同施肥处理各器官从肥料中吸收分配到的¹⁵N量对该器官全氮量的贡献率(Ndff)存在显著差异,盛花期均以根的Ndff最高,多年生枝次之;新梢旺长期和花芽分化期根部吸收的¹⁵N优先向新生营养器官转运;果实膨大期各器官Ndff均达到较高水平;果实成熟期均以果实中的Ndff最高.果实成熟期不同施肥处理的¹⁵N分配率存在显著差异,20 cm施肥处理生殖器官和营养器官的¹⁵N分配率显著高于0和40 cm施肥处理,而贮藏器官的¹⁵N分配率显著低于0和40 cm施肥处理.在果实成熟期,20 cm施肥处理¹⁵N肥料利用率为24.0%,显著高于0 cm(14.1%)和40 cm施肥处理(7.6%),而¹⁵N损失率为54.0%,显著低于0 cm(67.8%)和40 cm施肥处理(63.5%).不同施肥深度土壤¹⁵N残留量随施肥深度的增加而显著增加.     

等量分次施氮对冬枣15N和13C利用与分配特性的影响

以4年生盆栽冬枣为试材,采用¹³C、¹⁵N双标记示踪技术,在果实发育期研究了等氮量分次追施氮肥对冬枣植株¹⁵N和¹³C吸收、利用、积累和分配的影响.结果表明: 至果实采收期,冬枣各器官Ndff值(植株器官从肥料中吸收分配到的¹⁵N量对该器官全氮量的贡献率)随追氮次数的增多而显著增大.生殖器官(果实)和营养器官(叶片、枣吊、新生枣头枝和细根)的¹⁵N分配率以4次追氮处理最高,1次追氮处理最低,贮藏器官(主干、多年生枝和粗根)¹⁵N分配率的趋势相反;4次追氮处理¹⁵N利用率分别比1次和2次追氮处理高27.4%和15.5%.追氮次数越多,植株总氮量和¹⁵N吸收量越大;随时间的推移,1次追氮处理土壤¹⁵N丰度和总氮含量持续降低,2次追氮处理呈先升高后降低的趋势,4次追氮处理变化相对最为平稳,至处理后期显著高于其他处理;果实白熟至采收期,叶片叶绿素、氮含量和净光合速率均表现为4次追氮>2次追氮>1次追氮.不同处理¹³C同化物积累与分配不同.4次追氮处理¹³C固定总量分别是1次和2次追氮处理的1.1和1.2倍.增加追氮次数,促进了¹³C同化物向果实和贮藏器官的转移,而减少了向当年生营养器官的分配.综上,果实发育期4次追氮通过保证根层稳定、充足的氮素供应,提高了对氮素的吸收和利用,进而维持了较高的净光合速率,促进并优化了光合同化物的积累和分配,最有利于冬枣树体的生长及产量和品质的提高.     

控释氮肥和袋控肥对‘王林’苹果15N-尿素利用及其在土壤累积的影响

以6年生‘王林’/SH6/八棱海棠为试验材料,采用¹⁵N同位素示踪技术,研究了普通尿素(CU)、袋控缓释肥(BCRF)和控释氮肥(CRNF)对¹⁵N-尿素吸收、利用、损失和0～80 cm土层氮素累积动态的影响.结果表明: CRNF和BCRF处理较CU处理均明显提高了苹果生长后期土壤无机氮含量、果实成熟期叶片的SPAD值、氮含量、净光合速率和植株各器官对氮的吸收能力(Ndff值),但CRNF影响更显著.在0～40 cm土层不同物候期¹⁵N残留量呈降低趋势,均以CRNR最高,BCRF次之,CU最低,且CRNF降幅平缓,¹⁵N残留量主要集中在0～40 cm土层;在40～80 cm 土层不同物候期¹⁵N残留量呈增加趋势,均以CU最高,BCRF次之,CRNF最低,且CRNF增幅平缓.在果实成熟期,CRNF的¹⁵N肥料利用率为32.6%,分别是BCRF和CU 的1.11、1.56倍,而¹⁵N损失率为21.6%,显著低于BCRF(35.6%)和CU(59.6%).CRNF显著提高了果实产量,改善了果实品质,增加了经济效益.     

供氮水平对矮化苹果15N-尿素吸收、利用、损失及产量和品质的影响

以7年生烟富3/M26/平邑甜茶为试材,采用¹⁵N同位素示踪技术,研究不同供氮水平[低氮(100 kg N·hm^-2,N₁₀₀)、中氮(200 kg N·hm^-2,N₂₀₀)和高氮(300 kg N·hm^-2,N₃₀₀)]对烟富3/M26/平邑甜茶¹⁵N-尿素吸收、利用、损失及产量和品质的影响.结果表明: 不同供氮水平植株的生长状况及氮素吸收、利用和损失特性差异显著.N₂₀₀处理植株叶绿素含量(SPAD)、光合速率(P_n)、叶片全氮含量和生物量显著高于N₁₀₀和N₃₀₀处理,植株根冠比也显著增加.不同供氮水平下植株各器官对氮的吸收能力(Ndff值)存在显著差异,各测定时期果实(花)、叶片、一年生枝、多年生枝和中心干的Ndff值均为N₁₀₀>N₂₀₀＞N₃₀₀;而根的Ndff值在盛花期和春梢缓长期为N₁₀₀ >N₂₀₀＞N₃₀₀,在秋梢生长期、果实膨大期和果实成熟期为N₂₀₀ >N₁₀₀＞N₃₀₀.在果实成熟期,N₂₀₀处理¹⁵N肥料利用率为23.6%,显著高于N₁₀₀(16.3%)和N₃₀₀处理(14.4%),而¹⁵N损失率为56.4%,显著低于N₁₀₀(60.6%)和N₃₀₀处理(66.1%).不同供氮水平植株的平均单果质量、单株产量、可溶性固形物、硬度、可溶性糖、可滴定酸、糖酸比均存在显著差异,且均以N₂₀₀处理最高,其次是N₃₀₀处理,N₁₀₀处理最低.     

库尔勒香梨春季施用15N-尿素的吸收、分配和利用特性

以6年生库尔勒香梨为试材,在春季香梨萌芽前施用¹⁵N尿素,研究香梨施用¹⁵N尿素的吸收、分配和利用特性.结果表明:不同生育期香梨吸收的¹⁵N在各器官的分配率存在显著差异,盛花期¹⁵N优先分配在根中,其Ndff(从肥料中吸收的¹⁵N量对该器官全氮量的贡献率)最高,新稍次之;新梢旺长期和果实膨大期根部吸收的¹⁵N优先向新生器官(叶和新稍)运转,根部¹⁵N的分配率不断下降;果实成熟期果实成为新的分配中心,其Ndff最高,果实累积的¹⁵N量占香梨树体总的¹⁵N吸收量的19.8%.香梨树体对土施¹⁵N-尿素肥料的当季利用率随生育期的推进而不断提高,到果实成熟期达到最大值(18.5%).     

氮水平对苹果叶片13C光合产物和15N向果实转移分配的影响

以6年生‘烟富3’/M26/平邑甜茶苹果为试材,采用C、N双标记技术,研究在果实膨大后期用不同尿素浓度水溶液(N 0%、0.6%、1.2%、1.8%、2.4%,分别用CK、N₁、N₂、N₃、N₄表示)涂抹果实周围20 cm范围内叶片对叶片¹³C同化能力及¹³C光合产物、¹⁵N向果实转移分配的影响.结果表明: 随着尿素浓度的增加,叶片的叶绿素含量、氮含量、光合速率、山梨醇和蔗糖含量、6-磷酸山梨醇脱氢酶(S6PDH)和蔗糖磷酸合酶(SPS)活性及¹³C同化能力均先升高后降低,均以1.8%尿素涂抹处理最高,清水对照最低.¹³C自留量(自身叶片+自身新梢)以清水对照最高,为81.6%,1.8%尿素涂抹处理最低,为63.5%.向外输出的¹³C光合产物主要分布在标记果实,其次是未标记多年生枝,未标记叶片最低.果实¹³C吸收量随着尿素浓度增加呈先升高后降低趋势,以1.8%尿素涂抹处理最高(1.21 mg·g^-1),清水对照最低(0.51 mg·g^-1);果实¹⁵N吸收量随着尿素浓度增加呈持续升高趋势.表明尿素水溶液叶施可不同程度地提高叶片光合产物和氮素向果实转移分配的能力,以1.8%尿素涂抹处理叶片光合产物向果实转移分配能力最强,同时避免了过多的氮素向果实的输入.     

应用15N示踪研究欧美杨对PM2.5无机成分NH4+和NO3-的吸收与分配

通过气溶胶发生系统模拟PM2.5颗粒的发生,运用15N示踪技术研究了欧美杨107(Populus euramericana Neva.)对PM2.5中水溶性无机成分NH+4和NO-3的吸收与分配规律。结果表明,欧美杨能够有效吸收PM2.5中的NH+4和NO-3。轻度和重度污染下,欧美杨叶片对NH+4和NO-3的吸收速率均于处理后第1天达到峰值,之后,轻度污染下对NH+4和NO-3的吸收速率迅速降低以后趋于稳定,而重度污染下对NH+4和NO-3的吸收速率缓慢下降至趋于稳定。轻度污染下的欧美杨叶片的15N含量在处理后第1天达到峰值,15N(NH+4)的含量为0.11 mg/g,干重,15N(NO-3)的为0.14 mg/g,干重,之后15N含量迅速下降至趋于稳定。重度污染下的叶片15N含量在处理第1天迅速增长,之后缓慢增长至处理后第7天达到最高值,15N(NH+4)的含量为0.11 mg/g,干重,15N(NO-3)的为0.13 mg/g,干重。处理7 d后,欧美杨不同组织器官吸收或通过再分配获取的15N含量存在差异。轻度污染下,细根对NH+4和NO-3的吸收量最高,树皮、叶柄、叶片次之,髓最低。而重度污染下,叶片对NH+4和NO-3的吸收量最高,细根、叶柄、树皮次之,髓最低。欧美杨各组织器官中NH+4和NO-3的含量均表现为重度污染大于轻度污染,且两种污染程度下的欧美杨各组织器官对NO-3的吸收均大于对NH+4的吸收。重度污染下,欧美杨茎木质部对15N(NH+4和NO-3)的吸收征调能力(Ndff,Nitrogen derived from fertilizer)最大,其次为髓,叶片最小;欧美杨各组织器官中的15N分配率表现为叶片细根叶柄树皮粗根茎木质部髓。研究结果对进一步揭示植物吸收PM2.5的机制及有效利用植物降低颗粒物污染、净化环境提供了重要的科学理论依据。     

Mechanism of the gas phase reactions of the C5H5Ni and C5H5Co ions with substituted pyridines. A combined experimental and theoretical study

Different products have been observed in the reactions of C₅H₅Co⁺ and C₅H₅Ni⁺ ions with halogen-substituted pyridines (XPy) that have been studied by ion trap mass spectrometry (ITMS) techniques. In particular, an addition product C₅H₅M(XPy)⁺ and a product ion C₅H₄M(Py)⁺ corresponding to a loss of a HX molecule (X = F, Cl, Br) have been detected. The relative yield of these products is determined by the nature of the metal and by the nature and position of the halogen on the pyridine ring. A computational study at the DFT level on model-systems formed by 2-fluoro and 2-bromopyridine reacting either with the C₅H₅Ni⁺ or the C₅H₅Co⁺ ion has been carried out. This study shows the existence of a general mechanistic pattern. The rate-determining step of this mechanism is the migration of the halogen from the pyridine ring to the metal. A final hydrogen abstraction step carried out by the halogen leads to the expulsion of a HX molecule. The existence of avoided crossings between surfaces of different multiplicities (ground and first excited state) allows the system to follow lower energy reaction pathways. The barrier determined for the reactions involving 2-bromopyridine is significantly lower than that found for 2-fluoropyridine. This is mainly due to the poor migrating/leaving character and low polarizability of fluorine compared to that of bromine.     

MeJA诱导的拟南芥保卫细胞H2O2积累与质膜H+-ATPase的关系

茉莉酸类物质(JAs)作为与昆虫啃噬及损伤相关的植物激素和信号分子在植物防御反应中起重要作用,但是茉莉酸引起的早期防御反应的机理仍不清楚。该研究以拟南芥叶片保卫细胞为材料,结合非损伤微测(NMT)及激光共聚焦技术探讨了茉莉酸诱导的保卫细胞中质膜H+-ATPase与H2O2积累的调控关系。结果表明:茉莉酸甲酯(MeJA)处理导致H+迅速跨膜外排和H2O2积累,H+外排和H2O2积累能够被钒酸钠抑制,而二苯基碘(DPI)处理则对MeJA诱导的H+跨膜外排无显著影响。研究结果证明,在MeJA诱导的早期信号事件中,质膜H+-ATPase的激活先于H2O2的产生。     

HIV/AIDS患者抗病毒治疗前HIV-1耐药情况调查及外周血CD8+T细胞CD38表达水平研究

摘要 目的：分析人免疫缺陷病毒/艾滋病（HIV/AIDS）患者抗病毒治疗前HIV-1耐药以及影响因素,探讨HIV/AIDS患者外周血CD₈⁺T细胞CD₃₈表达（CD₈⁺CD₃₈⁺T淋巴细胞百分比）与CD₄⁺T淋巴细胞计数的相关性。方法：选择2016年3月至2019年12月我院接诊的442例HIV/AIDS患者（HIV/AIDS组）和163例同期于我院进行体检的健康志愿者（对照组）,HIV/AIDS组扩增pol基因,进行HIV-1基因耐药分析,检测CD₈⁺CD₃₈⁺T淋巴细胞百分比、CD₄⁺T淋巴细胞计数、CD₈⁺T淋巴细胞计数。分析HIV/AIDS患者HIV-1耐药的影响因素,分析CD₈⁺CD₃₈⁺T淋巴细胞百分比与CD₄⁺T淋巴细胞计数、CD₈⁺T淋巴细胞计数相关性。结果：HIV/AIDS组442例HIV/AIDS患者中376例获得HIV-1 pol基因序列,HIV-1耐药35例,耐药率9.31%（35/376）。单因素分析结果显示耐药组和非耐药组在年龄、文化程度、感染途径、HIV病毒载量方面差异有统计学意义（P＜0.05）。多因素Logistic回归分析结果显示同性性传播、注射吸毒、高HIV病毒载量是HIV/AIDS患者抗病毒治疗前HIV-1耐药的危险因素（P＜0.05）。HIV/AIDS组外周血CD₄⁺T淋巴细胞计数、CD₈⁺T淋巴细胞计数低于对照组（P＜0.05）,CD₈⁺CD₃₈⁺T淋巴细胞百分比高于对照组（P＜0.05）。CD₈⁺CD₃₈⁺T淋巴细胞百分比与CD₄⁺T淋巴细胞计数、CD₈⁺T淋巴细胞计数呈负相关（P＜0.05）。结论：抗病毒治疗前HIV/AIDS患者存在一定HIV-1耐药率,传播途径、HIV-1病毒载量与HIV-1耐药有关。CD₈⁺T细胞表面CD₃₈过表达与HIV/AIDS 患者CD₄⁺T T细胞的过度消耗有关。     

胞外ATP对AlCl3诱导的细胞死亡过程中胞内H2O2和Ca2+水平的影响及其生理机制分析

该实验以烟草悬浮细胞 BY 2 为材料,在烟草悬浮细胞中分别加入0.05、0.10、0.15、0.20 mmol·L^-1AlCl₃,以等体积去离子水处理的悬浮细胞液为对照,并依据前述实验结果选择0.15 mmol·L^-1 AlCl₃,分别添加5 mmol·L^-1 DMTU(H₂O₂ 抑制剂)、20 μmol·L^-1CaCl₂、15 μmol·L^-1 LaCl₃(Ca²⁺通道抑制剂)和50 μmol·L^-1 ATP设计多项处理,分析胞外ATP(eATP)对铝离子(Al³⁺)胁迫引起的植物细胞死亡及其胞内H₂O₂、Ca²⁺的影响,以揭示Al³⁺胁迫下植物调节细胞死亡的可能机制,进一步扩展对eATP功能的认知。结果显示：(1)随着 AlCl₃ 胁迫浓度的提高,细胞死亡水平和胞内H₂O₂水平上升,而胞内Ca²⁺和eATP水平则逐渐降低。(2)外援施加H₂O₂抑制剂 DMTU(二甲基硫脲)和Ca²⁺能够有效缓解AlCl₃诱导的细胞死亡水平的上升;而Ca²⁺通道抑制剂LaCl₃(三氯化镧)则加剧了AlCl₃胁迫下的细胞死亡。(3)在AlCl₃胁迫下对细胞添加外源ATP,能够缓解AlCl₃胁迫下胞内H₂O₂水平上升和Ca²⁺水平下降的同时,并显著降低AlCl₃胁迫导致的细胞死亡。研究表明, Al³⁺以剂量依赖的模式提升细胞死亡和细胞内H₂O₂的水平并降低胞内Ca²⁺和eATP水平,AlCl₃诱导的细胞死亡受到H₂O₂和Ca²⁺水平变化的调节,eATP可以通过调节H₂O₂与Ca²⁺水平缓解AlCl₃诱导的细胞死亡。推测Al³⁺胁迫可能通过抑制钙离子通道而破坏了细胞内H₂O₂和Ca²⁺之间的协同关系,外源ATP对Al³⁺诱导H₂O₂上升的缓解作用可能是由于其提升了细胞的抗氧化能力。     

Involvement of aquaporin in thromboxane A2 receptor-mediated, G12/13/RhoA/NHE-sensitive cell swelling in 1321N1 human astrocytoma cells

The physiological role of the thromboxane A₂ (TXA₂) receptor expressed on glial cells remains unclear. We previously reported that 1321N1 human astrocytoma cells pretreated with dibutyryl cyclic AMP (dbcAMP) became swollen in response to U46619, a TXA₂ analogue. In the present study, we examined the detailed mechanisms of TXA₂ receptor-mediated cell swelling in 1321N1 cells. The cell swelling caused by U46619 was suppressed by expression of p115-RGS, an inhibitory peptide of Gα_12/13 pathway and C3 toxin, an inhibitory protein for RhoA. The swelling was also inhibited by treatment with Y27632, a Rho kinase inhibitor and 5-(ethyl-N-isopropyl)amiloride (EIPA), a Na⁺/H⁺-exchanger inhibitor. Furthermore, cell swelling was suppressed by the pretreatment with aquaporin inhibitors mercury chloride or phloretin in a concentration-dependent manner, suggesting that aquaporins are involved in U46619-induced 1321N1 cell swelling. In fact, U46619 caused [³H]H₂O influx into the cells, which was inhibited by p115-RGS, C3 toxin, EIPA, mercury chloride and phloretin. This is the first report that the TXA₂ receptor mediates water influx through aquaporins in astrocytoma cells via TXA₂ receptor-mediated activation of Gα_12/13, Rho A, Rho kinase and Na⁺/H⁺-exchanger.     

The effect of F0 inhibitors on the Vibrio alginolyticus membrane ATPase

The inhibition of membrane ATPase from the marine alkalotolerant bacterium Vibrio alginolyticus by DCCD, triphenyltin and venturicidin was studied. DCCD proved to be an irreversible inhibitor, while venturicidin and triphenyltin produced a reversible inhibitory effect. The DCCD-binding proteolipid was identified in the membrane preparations. The effect of the inhibitors on ATPase activity and ATP-dependent Na⁺-transport in V. alginolyticus subcellular vesicles is discussed.     

Estimation of symbiotically fixed nitrogen in field grown soybeans: An application of natural15N/14N abundance and a low level15N-tracer technique

Summary Plants from agricultural and natural upland ecosystem were investigated for¹⁵N content to evaluate the role of symbiotic N₂-fixation in the nitrogen nutrition of soybean. Increased yields and lower δ¹⁵N values of nodulating soybeansvs, non-nodulating isolines gave semi-quantitative estimates of N₂ fixation. A fairly large discrepancy was found between estimations by δ¹⁵N and by N yield at 0 kg N/ha of fertilizer. More precise estimates were made by following changes in plant δ¹⁵N when fertilizer δ¹⁵N was varied near¹⁵N natural abundance level. Clearcut linear relationships between δ¹⁵N values of whole plants and of fertilizer were obtained at 30 kg N/ha of fertilizer for three kinds of soils. In experimental field plots, nodulating soybeans obtained 13±1% of their nitrogen from fertilizer, 66±8% from N₂ fixation and 21±10% from soil nitrogen in Andosol brown soil; 30%, 16% and 54% in Andosol black soil; 7%, 77% and 16% in Alluvial soil, respectively. These values for N₂ fixation coincided with each corresponding estimation by N yield method. Other results include: 1)¹⁵N content in upland soils and plants was variable, and may reflect differences in the mode of mineralization of soil organics, and 2) nitrogen isotopic discrimination during fertilizer uptake (δ¹⁵N of plant minus fertilizer) ranged from −2.2 to +4.9‰ at 0–30 kg N/ha of fertilizer, depending on soil type and plant species. The proposed method can accurately and relatively simply establish the importance of symbiotic nitrogen fixation for soybeans growing in agricultural settings.     

Biological function of modified nucleotides T54 and Ψ55 of yeast tRNAAla

The 3′ half molecule of yeast tRNA^Ala (nucleotides 36–75) was hybridized with a DNA fragment (5′GGAATCGAACC 3′) and the hybrid was then digested withE. coli RNase H (from Boehringer). The enzyme can specifically cleave the 3′ half molecule at the 3′ side of nucleotide Ψ₅₅, thus a fragment C₃₆-Ψ₅₅ was prepared. The 3′-terminal T or TΨ of this fragment was removed by one or two cycles of periodate oxidation and β-elimination. The products were fragments C₃₆-T₅₄ and C₃₆-G₅₃. Three yeast tRNA_Ala fragments C₅₆-A₇₆, U₅₅-A₇₆ (with Ψ₅₅ replaced by U), U₅₄-A₇₆ (with T₅₄Ψ₅₅ replaced by UU) were synthesized and ligated with three prepared fragments (C₃₆-Ψ₅₅, C₃₆-T₅₄ and C₃₆-G₅₃) respectively by T4 RNA ligase. The products were further ligated with the 5′ half molecule (nu-cleotides 1–35). Using this method, one reconstituted yeast tRNA^Ala (tRNAr) and two yeast tRNA^ALa analogs: (i) tRNAa with U₅₅ instead of Ψ₅₅; (ii) tRNAb with U₅₄U₅₅ instead of T₅₄Ψ₅₅ were synthesized. The charging and incorporation activities of these three tRNAs were determined. In comparison with the reconstituted tRNA, the charging activity was 75% for tRNAa and 45% for tRNAb and the incorporation activity was 65% for tRNAa and 70% for tRNAb. These results suggest that the modified nucleotides T₅₄ and Ψ₅₅ play an important role in yeast tRNA^Ala function. Project supported by the National Natural Science Foundation of China.     

Synthesis and characterization of three group 10 complexes containing nido-carborane diphosphine: [MCl(PPh3){7,8-(PPh2)2-7,8-C2B9H10}] (M = Ni, Pd, Pt)

Three group 10 complexes containing nido-carborane diphosphine, [NiCl(PPh₃){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] (1), [PdCl(PPh₃){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] · 1.25CH₂Cl₂ (2) and [PtCl(PPh₃){7,8-(PPh₂)₂-7,8-C₂B₉H₁₀}] · 2.5CH₂Cl₂ (3) have been synthesized by the reactions of [M(PPh₃)₂Cl₂] (M = Ni, Pd, Pt) with closo carborane diphosphine 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ in ethanol. For complex 3, it could also be obtained under solvothermal condition. All three complexes were characterized by elemental analysis, FT-IR, ¹H and ¹³C NMR spectroscopy and X-ray structure determination. Single crystal structures show that their structures are similar to each other. In each complex, the nido [7,8-(PPh₂)₂-7,8-C₂B₉H₁₀]⁻, which resulted from the degradation of the initial closo ligand 1,2-(PPh₂)₂-1,2-C₂B₁₀H₁₀ during the reaction process, was coordinated bidentately through the P atoms to M(II) ion, and this resulted in a stable five-membered chelating ring between the bis-diphosphine ligand and the metal. The coordination mode of the metal can be described as a slightly distorted square-planar, in which the remaining two positions were occupied by one Cl⁻ and one PPh₃ group.