中华倒刺鲃幼鱼能量代谢特征个体差异及生态关联

为了探讨鱼类能量代谢特征个体变异及其生态关联, 以中华倒刺鲃(Spinibarbus sinensis)幼鱼为实验对象, 在25℃条件下测定44尾实验鱼的静止代谢率(Resting metabolic rate, RMR)、力竭运动后峰值代谢率(Peak metabolic rate, PMR)、力竭运动后过量耗氧(Excess post-exercise oxygen consumption, EPOC)、低氧胁迫后峰值代谢率PMR和低氧胁迫后过量耗氧(Excess post-hypoxia oxygen consumption, EPHOC)。研究发现, 中华倒刺鲃能量代谢特征参数存在较大个体差异, RMR、力竭运动后PMR、EPOC、低氧胁迫后PMR和EPHOC分别为193.62—460.33 [mg O₂/(kg·h)]、617.9—2165.02 [mg O₂/(kg·h)]、28.76—267.20 mg O₂/kg、484.3—1142.97 [mg O₂/(kg·h)]和30.27—211.88 mg O₂/kg。力竭运动后PMR(r=0.348, P=0.010)和低氧胁迫后PMR(r=0.449, P=0.002)与RMR间均呈显著正相关; EPOC与RMR间呈显著负相关(r=–0.426, P=0.004), 而EPHOC与RMR间的关系不显著(r=–0.292, P=0.054); 力竭运动后PMR与EPOC间(r=0.424, P=0.004)和低氧胁迫后PMR与EPHOC间(r=0.391, P=0.009)均呈显著正相关。力竭运动后PMR与低氧胁迫后PMR(r=0.673, P<0.001)和EPOC与EPHOC(r=0.526, P<0.001)在个体差异均显著正相关; 然而力竭运动后PMR和EPOC分别显著高于低氧胁迫后PMR与EPHOC(P<0.05)。研究表明: 维持代谢较高的中华倒刺鲃个体有助于其快速提升有氧功率输出以维持高的游泳运动能力; 而较低维持代谢个体具有相对较高的EPHOC有助于机体在极端环境条件下提升其低氧耐受能力。中华倒刺鲃能量特征的个体变异可能是经长期自然选择适应环境的结果。     

食物丰度对宽鳍鱲的能量代谢、个性和集群行为的影响

水生生境中的食物资源经常变化,鱼类的能量代谢和行为随食物丰度改变的可塑性调节具有重要的进化和生态意义。为考察食物丰度对机体行为和代谢的影响,以雌性宽鳍鱲（Zacco Platypus）为实验对象,分别测定实验鱼在高、低食物丰度组4周喂养期前后的标准代谢率（Standard metabolic rate,SMR）、个性及集群行为。研究发现：（1）经4周喂养,高食物丰度组的体重和SMR上升,而低食物丰度组维持不变,喂养期结束时高食物丰度组的体重和SMR均显著大于低食物丰度组;（2）食物丰度对个性没有显著影响,但集群时,低食物丰度组活跃性较高,凝聚力较低;（3）高食物丰度下SMR保持稳定,低食物丰度下SMR不稳定。研究表明：宽鳍鱲的个性不受食物丰度影响;但食物丰度减少导致能量代谢下降、鱼群活跃性上升和凝聚力下降,可能与食物丰度较低时代谢的适应性下调和食物资源竞争加剧导致的觅食活动需求上升相关。     

北京典型树种木质组织碳释放速率温度敏感性的时间变化规律和铅锤分异特征

采用红外气体分析法(IRGA)于2014年1—12月原位测定了北京市4个典型树种(国槐Sophora japonica,旱柳Salix matsudana,华北落叶松Larix principis-rupprechtii和侧柏Platycladus orientalis)在不同高度上的木质组织CO_2通量速率(E_(CO_2)),旨在比较不同树种间E_(CO_2)及其温度敏感性(Q_(10))的时间变化规律和铅锤分异特征。研究结果显示:(1)4个树种的E_(CO_2)均表现为单峰型季节变化规律,生长月份内的E_(CO_2)显著高于非生长月份,温度和枝干的径向生长是影响E_(CO_2)季节变化的主要因素;(2)E_(CO_2)对温度的敏感性在夏季月份明显降低,且出现明显的垂直分异:Q_(10)随测量高度的增加而增加,呈现出非连续的阶梯分布;(3)在日间尺度上,阔叶树种E_(CO_2)对温度的感性系数Q_(10)出现昼夜不对称现象,晚上Q_(10)明显升高。准确量化E_(CO_2)的时间变化规律和铅锤分异特征,细化不同时间尺度下E_(CO_2)对温度的响应特征,成为准确估算木质组织碳排放的前提条件。     

毛白杨树干呼吸及其温度敏感性季节变化特征

树干呼吸(E_s)是森林生态系统碳循环过程的重要组成部分,深入理解树干呼吸过程对未来气候变暖的响应及反馈机制有助于更加精确地估算森林生态系统碳储量。为揭示毛白杨树干呼吸及其温度敏感性的昼夜变化和季节动态规律,利用Li-Cor6400便携式光合作用测定系统及其配套使用的土壤呼吸测量气室(LI-6400-09)对冀南平原区毛白杨的树干呼吸和树干温度实施为期1年的连续监测。结果表明:(1)在生长季,毛白杨树干呼吸与树干温度之间在晚上呈现正相关的关系(R~2=0.88);相反,两者在白天为负相关的关系(R~2=0.96)。(2)整个观测期内,毛白杨树干呼吸和树干温度均呈现\"钟形\"的变化曲线,树干呼吸与树干温度之间存在着较好的指数函数关系(R~2=0.93),且树干呼吸的温度敏感性系数(Q_(10))为2.62;不同季节毛白杨树干呼吸的Q_(10)存在差异,生长季的Q_(10)(1.95)明显低于非生长季(3.00),表明生长呼吸和维持呼吸对温度的响应也并不相同。(3)温度矫正后的毛白杨树干呼吸(R_(15))在昼夜和季节尺度上均存在明显的变异,即夜晚的R_(15)显著高于白天(P0.01),生长季的R_(15)明显高于非生长季(P0.05);树干可溶性糖含量与生长季的R_(15)存在较好的相关性(R~2=0.52),而非生长季的R_(15)却主要受到树干淀粉含量的影响。研究结果表明,在生长季,毛白杨树干呼吸的在日变化主要受到温度的影响,而在季节尺度上Q_(10)的变异则与树干呼吸中维持呼吸所占比例及树干中非结构性碳水化合物(可溶性糖和淀粉)的含量及类型紧密相关。     

温度对宽鳍鱲运动能力和行为特征的影响

为了探究温度对宽鳍鱲(Zacco platypus)运动能力和行为特征的影响,分别在15和25℃的水温下对捕捞自乌江重庆武隆段的宽鳍鱲进行了为期3周的温度驯化,随后对其临界游泳能力、快速启动能力和行为特征(活跃性和隐匿行为)进行了测定。结果表明:相比25℃组,低温下(15℃)实验鱼临界游泳速度、最大代谢率、日常代谢率和代谢范围均显著降低(P0.05);低温下快速启动参数中最大速度、最大加速度和120 ms移动位移均显著降低(P0.05),但反应时滞无显著变化;此外,低温下实验鱼活跃性显著降低,而隐匿行为显著增加(P0.05);提示低温下宽鳍鱲运动能力的整体水平显著下降,对温度反应较为保守的快速启动反应时滞可能是低温下宽鳍鱲应对捕食压力的重要方式,而行为上降低活跃性和提高隐匿行为可能是对运动能力降低的补偿。     

Septoria的新种和国内新记录种

作者在1987-1991年间从东北地区收集和采集Septoria真菌标本221份,鉴定出Septoria 84种,其中2个新种:Septoria dioscorical Lu Guo-zhong et Bai Jin-kai和Septoria saposhinikoviae Lu Guo-zhong et Bai Jin-kai,以及13个国内新记录种. Septoria属真菌的产孢方式为全壁芽生合轴式(holoblastic sympodial)。     

黄花棘豆脱水素OoY2K4的鉴定及表达分析

该研究以黄花棘豆cDNA为模板,采用同源克隆法,从黄花棘豆转录组数据库中克隆获得1个响应逆境胁迫的胚胎发育晚期丰富蛋白基因,命名为OoY_2K_4;OoY_2K_4基因ORF为786bp,编码261个氨基酸,含有2个保守的Y片段和4个K片段,为典型的Y_2K_4类脱水蛋白亚家族成员;OoY_2K_4蛋白不具有跨膜结构域,不存在信号肽,亲水性极强,含有1个糖基化位点和17个磷酸化位点;亚细胞定位显示,OoY_2K_4蛋白定位于细胞质中。多序列比对发现,OoY_2K_4蛋白与其他物种第二组LEA蛋白(脱水素)序列高度保守;进化树分析显示,该序列与三叶草、蒺藜苜蓿和紫花苜蓿相似度最高,亲缘关系最近。采用qRT-PCR对OoY_2K_4基因在干旱、高盐、低温以及脱落酸、乙烯、赤霉素处理下的表达分析显示,干旱和高盐胁迫可显著诱导OoY_2K_4基因表达,而低温胁迫下基本无变化;激素处理均可诱导OoY_2K_4基因高效表达,其中脱落酸诱导下OoY_2K_4基因表达最显著。研究推测,OoY_2K_4基因可能通过依赖ABA的信号途径参与黄花棘豆对干旱和高盐逆境胁迫的应答反应。     

全球陆地生态系统光合作用与呼吸作用的温度敏感性

基于全球647套通量数据,定量分析了全球尺度下生态系统光合作用和呼吸作用的温度敏感性(Q10)随纬度、气候和植被的分布规律。结果表明:在全球尺度下,光合作用和呼吸过程的温度敏感性(Q10,G和Q10,R)都随纬度的升高而增加,其中Q10,G和Q10,R的均值分别为3.99±0.21和2.28±0.074。除热带多树草原、常绿落叶林外,Q10,G均大于Q10,R值。不同植被类型的温度敏感性存在显著性差异,表现为:针叶林阔叶林;落叶林常绿林,其中生态系统的季节性变异是造成差异的主要原因。当植被类型和纬度区域共同影响Q10值时,植被类型对Q10值的总变异贡献更大。气候类型对Q10,G和Q10,R都有显著影响。在气候带上,干旱带的Q10,G最小,而冷温带的Q10,G最高。不同气候类型下(除温带草原气候外)的Q10,G都大于Q10,R。在极端条件下,温度可能不在是主导因素,而水分对温度敏感性的影响不可忽略,今后的研究需要更多的关注生态系统温度敏感性对水分变化的响应。     

浅表层水稻土N2O消耗能力及其与N2O还原微生物的耦合关系

土壤不仅能够产生、排放温室气体N_2O,还具有截留、吸收、转化N_2O的能力。土壤消耗N_2O已经成为很重要的一种降低大气N_2O浓度的途径,但目前关于土壤N_2O消耗过程及其微生物调控机制的系统研究较为缺乏。试验以浅表层水稻土柱(0—5 cm)为研究对象,通过外源添加N_2O气体研究N_2O迁移通过淹水土柱的动态过程,以及N_2O消耗能力与氧化亚氮还原酶基因丰度变化和其他土壤养分含量变化的联系,揭示浅表层水稻土N_2O消纳量与N_2O还原微生物之间的耦合关系。结果显示,淹水厌氧条件下5 cm土壤深度外源添加的N_2O迁移通过浅表层土柱后,仅有7.17—9.80%部分逸散出土表,表明0—5 cm淹水水稻土层具有极强的N_2O截留能力(90%以上)而减少N_2O净排放量。排放出土表的N_2O也可被淹水土柱继续吸收消耗,且吸收转化速率随N_2O浓度增加而大幅提高,最高可达到3896.75μg N m~(-2) h~(-1)。与此同时,土壤DOC含量大量消耗,含nosZⅠ基因的反硝化微生物数量显著增长(P0.01),而nosZⅡ基因丰度的无显著变化。说明高浓度N_2O添加能够促进淹水土壤N_2O吸收消耗能力,此刺激作用可能主要由含nosZⅠ基因的N_2O还原微生物进行调控。浅表层土壤强大的N_2O吸收消耗功能可进一步深入系统研究,为实践温室气体减排提供理论基础。     

THINOPYRUM BESSARABICUM和THINO-PYRUM ELONGATUM的基因组关系研究

对 2个八倍体 C.S- Thinopyrum bessarabicum( AABBDDJJ,2 n=8x=56)和 Goshawk( GHK) - Thinopyrum elongatum( AABBDDEE,2 n=8x=56)的根尖细胞染色体进行 C-分带 ,从中分检出 Th.bessarabicum和 Th.elongatum的各自染色体进行核型分析 ,结果表明 :Th.bessarabicum和 Th.elongatum的大多数染色体都具有端带 ,但 Th.bessarabicum的端带更强 ,很少有中间带 ;而 Th.elongatum的染色体除 E1外其它染色体的端带较弱 ,而且带纹较丰富 ,有较多的中间带。对 C.S- Th.bessarabicum和 GHK- Th.elongatum进行有性杂交 ,其杂交种F1的 PMC染色体在 MI的平均配对构型为 1 5.50 5.0 3 [ 1 4.2 0 ○ 0 .40 0 .2 1 ,其中 Th.bessarabicum和 Th.elongatum染色体平均配对成 2 .5个二价体 ,由 C-分带显示大多数 Th.bessarabicum和 Th.elongatum染色体呈单价体状态。因此推断 ,Th.bessarabicum和 Th.elongatum两物种的染色体应属不同的染色体组     

Thermal sensitivity of metabolic rates and swimming performance in two latitudinally separated populations of cod, <Emphasis Type="Italic">Gadus morhua</Emphasis> L.

Atlantic cod populations live in a wide thermal range and can differ genetically and physiologically. Thermal sensitivity of metabolic capacity and swimming performance may vary along a latitudinal gradient, to facilitate performance in distinct thermal environments. To evaluate this hypothesis, we compared the thermal sensitivity of performance in two cod stocks from the Northwest Atlantic that differ in their thermal experience: Gulf of St Lawrence (GSL) and Bay of Fundy (BF). We first compared the metabolic, physiological and swimming performance after short-term thermal change to that at the acclimation temperature (7°C) for one stock (GSL), before comparing the performance of the two stocks after short-term thermal change. For cod from GSL, standard metabolism (SMR) increased with temperature, while active metabolism (AMR, measured in the critical swimming tests), EMR (metabolic rate after an exhaustive chase protocol), aerobic scope (AS) and critical swimming speeds (U _crit and U _b–c) were lower at 3°C than 7 or 11°C. In contrast, anaerobic swimming (sprint and burst-coasts in U _crit test) was lower at 11 than 7 or 3°C. Factorial AS (AMR SMR⁻¹) decreased as temperature rose. Time to exhaustion (chase protocol) was not influenced by temperature. The two stocks differed little in the thermal sensitivities of metabolism or swimming. GSL cod had a higher SMR than BF cod despite similar AMR and AS. This led factorial AS to be significantly higher for the southern stock. Despite these metabolic differences, cod from the two stocks did not differ in their U _crit speeds. BF cod were better sprinters at both temperatures. Cod from GSL had a lower aerobic cost of swimming at intermediate speeds than those from BF, particularly at low temperature. Only the activity of cytochrome C oxidase (CCO) in white muscle differed between stocks. No enzymatic correlates were found for swimming capacities, but oxygen consumption was best correlated with CCO activity in the ventricle for both stocks. Overall, the stocks differed in their cost of maintenance, cost of transport and sprint capacity, while maintaining comparable thermal sensitivities.     

生境不完全重叠的两种鲤科鱼类耐低氧及运动能力比较

以乌江流域亲缘关系近,但分布并不完全重叠的马口鱼(Opsariichthys bidens)和宽鳍鱲(Zacco platypus)作为实验对象,分别考察这两种实验鱼的低氧耐受及游泳运动能力。将野外采回的实验鱼置于(25±1)℃条件下,分别测定两种鱼的临界氧分压(Pcrit)、水面呼吸(ASR)、失去平衡点(LOE)以及在不同溶氧水平(8.0、4.0和2.0 mg/L)下的临界游泳速度(Ucrit)和活跃耗氧率(MO2active)。研究发现:马口鱼的Pcrit(2.44±0.20)mg/L显著高于宽鳍鱲(1.86±0.10)mg/L(P=0.031)。但马口鱼的50%ASR(1.23±0.16)mg/L显著低于宽鳍鱲(1.97±0.11)mg/L(P=0.023);马口鱼的50%LOE(0.84±0.01)mg/L同样显著低于宽鳍鱲(0.97±0.02)mg/L(P=0.004)。宽鳍鱲在8.0和4.0 mg/L下的游泳能力显著高于马口鱼,然而马口鱼和宽鳍鱲的Ucrit均随测定溶氧水平的下降而显著降低(P0.01);宽鳍鱲和马口鱼的运动耗氧率均随水流速度的增加而呈现指数增加,但随测定溶氧水平的降低运动耗氧曲线变得相对平缓,尤其是在溶氧为4.0 mg/L时马口鱼的运动耗氧曲线与宽鳍鱲相比越发平缓;两种实验鱼的MO2active随溶氧水平下降的变化趋势与Ucrit相似(P0.001)。结果表明:两种野外生存的实验鱼不仅在低氧耐受能力方面存在显著差异,而且两者的游泳运动能力也有不同表现,这很有可能与其遗传特征、生存环境及生态习性相关。     

Emission of hydrogen sulfide by twigs of coniferes — acomparison of Norway spruce (Picea abies (L.) Karst.), Scotch pine (Pinus sylvestris L.) and Blue spruce (Picea pungens Engelm.)

The emission of reduced volatile sulfur compounds from twigs of Norway spruce (Picea abies (L.) Karst.) was measured in the field by cryosampling and gaschromatographic analysis. Trees were growing in the Erzgebirge (E-Germany) at Oberbärenburg and at the Kahleberg and at a third stand in NW-Bavaria (S-Germany). Emission rates were also measured for Scotch pine (Pinus sylvestris L.) and Blue spruce (Picea pungens Engelm.) at the Kahleberg. Twigs still attached to the trees were enclosed in a flow-through gas exchange cuvette. H₂S was detected as the predominant reduced sulfur compound emitted from the twigs. The mean H₂S emission rate from twigs of Norway spruce varied between 0.04 pmol kg^-1 dw s^-1 at Würzburg and 6.21 pmol kg^-1 dw s^-1 at the Kahleberg. Comparing different species at the Kahleberg, the mean H₂S emission rate was almost the same from twigs of Norway spruce (6.2 pmol kg^-1 dw s^-1) and Blue Spruce trees (5.9 pmol kg^-1 dw s^-1) but it was approximately 18 times higher for Scotch pine (110 pmol kg^-1 dw s^-1). The percentage of SO₂-exclusion via H₂S-emission of the tree species investigated at the Kahleberg is calculated on the basis of data on SO₂ fluxes. It is very small for Norway spruce and Blue spruce. However, for Scotch pine, H₂S emission contributes about 10% to the detoxification of SO₂.     

Control of nitrate and nitrite assimilation by carbohydrate reserves,adenosine nucleotides and pyridine nucleotides in leaves of Zea mays L. under dark conditions

The rate of in-vivo nitrate reduction by leaf segments of Zea mays L. was found to decline during the second hour of dark anaerobic treatment. On transfer to oxygen the capacity to reduce nitrate under dark conditions was restored. These observations led to the proposal that nitrate reductase is a regulatory enzyme with ADP acting as a negative effector. The effect of ADP on the invitro activity of nitrate reductase and the changes in the in-vivo adenylate pool under dark-N₂ and dark-O₂ were investigated. It was found that ADP inhibited the activity of partially purified nitrate reductase. Similarly, the in-vivo anaerobic inhibition of nitrate reduction was associated with a build-up of ADP in the leaf tissue. Under anaerobic conditions nitrite accumulated and on transfer to oxygen the accumulated nitrite was reduced. To explain this phenomenon the following hypothesis was proposed and tested. Under anaerobic conditions the supply of reducing equivalents for nitrite reduction in the plastid becomes restricted and nitrite accumulates as a consequence. On transfer to oxygen this restriction is removed and nitrite disappears. This capacity to reduce accumulated nitrite was found to be dependent on the carbohydrate status of the leaf tissue.     

Comparison of gas chromatography-mass spectrometry,radioimmunoassay and bioassay for the quantification of gibberellin A9 in norway spruce (Picea abies (L.) Karst.)

Quantitative estimates of gibberellin A₉ in Norway spruce extracts obtained by gas chromatography-mass spectrometry, radioimmunoassay (RIA_ and bioassay were compared after successive purifications of the extracts. The extracts were assayed in several dilutions with and without the addition of standard gibberellin A₉, thus showing the effect of extract components on the response of the assays. Radioimmunoassay produced estimates comparable to gas chromatography-mass spectrometry after one purification step by high-performance liquid chromatography. Extracts purified by polyvinylpyrrolidone-column chromatography and solvent partitioning but not high-performance liquid chromatography resulted in inaccurate RIA estimates. The performance of the RIA could be monitored by logit-log transformations of the standard curve and extract dilution curve and by calculating the slope of the standard addition curve. It was, however, not possible to correct for the interference caused by extract components by the standard addition procedure. Quantifications by Tan-ginbozu dwarf-rice bioassay were accurate, but a large and unpredictable variation makes it unsuitable for quantitative determinations.Abbreviations FW fresh weight - GA₉ gibberellin A₉ - GA₉–Me methylated GA₉ - GC-MS gas chromatography-mass spectrometry - HPLC high performance liquid chromatography - MID multiple-ion detection - RIA radioimmunoassay     

外源CaCl2对NaCl胁迫下酸枣幼苗氮代谢的影响

为了研究CaCl₂对NaCl胁迫下酸枣幼苗根、茎、叶的氮代谢影响,探索钙缓解幼苗NaCl胁迫的作用途径。该研究以酸枣幼苗为试验材料,检测不同浓度CaCl₂(0、5、10、20 mmol/L)对NaCl(150 mmol/L)胁迫下幼苗叶片H₂O₂、O^-·₂含量,根、茎、叶中硝酸还原酶(NR)、谷氨酰胺合成酶(GS)、谷氨酸合酶(GOGAT)活性及游离氨基酸、可溶性蛋白、硝态氮含量的影响,并采用主成分分析法筛选出评价CaCl₂缓解NaCl胁迫效应的生理指标。结果表明：与NaCl胁迫相比,盐胁迫幼苗叶片的H2O₂、O^-·₂积累量在5、10 mmol/L CaCl₂处理下显著减少;GOGAT活性在5、10 mmol/L CaCl₂处理下的植株根和茎内以及各浓度 CaCl₂处理的叶内均显著升高, GS、NR活性在10、20 mmol/L CaCl₂处理的根内和10 mmol/L CaCl₂处理的茎内以及5、10、20 mmol/L CaCl₂处理的叶内均显著升高;可溶性蛋白含量在5、10、20 mmol/L CaCl₂处理的根、茎、叶内均显著升高,游离氨基酸含量在10、20 mmol/L CaCl₂处理的根和茎内以及10 mmol/L CaCl₂处理的叶内均显著升高,硝态氮含量在10 mmol/L CaCl₂处理的根和茎内以及5、10、20 mmol/L CaCl₂处理的叶内均显著升高。研究发现,150 mmol/L NaCl胁迫对酸枣幼苗造成明显过氧化伤害,抑制了体内氮代谢;外源CaCl₂可通过促进幼苗根和茎内GS/GOGAT循环对NH₄⁺的同化作用,提高叶片NR活性,加快硝态氮的转化速率,从而增强幼苗对NaCl胁迫的适应性,并以10 mmol/L CaCl₂处理缓解效果最佳;游离氨基酸、GOGAT、NR可以作为CaCl₂缓解幼苗NaCl胁迫伤害的评价指标。     

Internode length in Zea mays L.

[¹³C, ³H]Gibberellin A₂₀ (GA₂₀) has been fed to seedlings of normal (tall) and dwarf-5 and dwarf-1 mutants of maize (Zea mays L.). The metabolites from these feeds were identified by combined gas chromatography-mass spectrometry. [¹³C, ³H]Gibberellin A₂₀ was metabolized to [¹³C, ³H]GA₂₉-catabolite and [¹³C, ³H]GA₁ by the normal, and to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₁ by the dwarf-5 mutant. In the dwarf-1 mutant, [¹³C, ³H]GA₂₀ was metabolized to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₂₉-catabolite; no evidence was found for the metabolism of [¹³C, ³H]GA₂₀ to [¹³C, ³H]GA₁. [¹³C, ³H]Gibberellin A₈ was not found in any of the feeds. In all feeds no dilution of ¹³C in recovered [¹³C, ³H]GA₂₀ was observed. Also in the dwarf-5 mutant, the [¹³C]label in the metabolites was apparently undiluted by endogenous [¹³C]GAs. However, dilution of the [¹³C]label in metabolites from [¹³C, ³H]GA₂₀ was observed in normal and dwarf-1 seedlings. The results from the feeding studies provide evidence that the dwarf-1 mutation of maize blocks the conversion of GA₂₀ to GA₁.Abbreviations GA_n gibberellin A_n - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - RP reverse phase     

The role of glutamate in swim initiation in the medicinal leech

Antagonists were used to investigate the role of the excitatory amino acid,l-glutamate, in the swim motor program ofHirudo medicinalis. In previous experiments, focal application ofl-glutamate or its non-NMDA agonists onto either the segmental swim-gating interneuron (cell 204) or the serotonergic Retzius cell resulted in prolonged excitation of the two cells and often in fictive swimming. Since brief stimulation of the subesophageal trigger interneuron (cell Tr1) evoked a similar response, we investigated the role of glutamate at these synapses. Kynurenic acid and two non-NMDA antagonists, 6,7-dinitroquinoxaline-2,3-dione (DNQX) and Joro spider toxin, effectively suppressed (1) the sustained activation of cell 204 and the Retzius cell following cell Tr1 stimulation and (2) the monosynaptic connection from cell Tr1 to cell 204 and the Retzius cell, but did not block spontaneous or DP nerve-activated swimming. Other glutamate blockers, including -d-glutamylaminomethyl sulfonic acid,l(+)-2-amino-3-phosphonoproprionic acid and 2-amino-5-phosphonopentanoic acid, were ineffective. DNQX also blocked both indirect excitation of cell 204 and direct depolarization of cell Tr1 in response to mechanosensory P cell stimulation. Our findings show the involvement of non-NMDA receptors in activating the swim motor program at two levels: (1) P cell input to cell Tr1 and (2) cell Tr1 input to cell 204, and reveal an essential role for glutamate in swim initiation via the cell Tr1 pathway.     

Purification and characterization of D-glycerate-3-kinase from maize leaves

Glycerate kinase (GK; EC 2.7.1.31) from maize (Zea mays L.) leaves was purified by a sequence of ammonium-sulfate precipitations and chromatography on diethylaminoethyl-cellulose, hydroxyapatite, Sephadex G-75SF and dye ligand (Green A) columns. The purest preparation was almost 1300-fold enriched and had a specific activity of 68 mol · min^-1 · (mg protein) ^-1. The enzyme was a monomer of a relative molecular mass (M_r) of 44 kDa (kdalton) as determined by gel filtration, electrophoresis in dissociating conditions and by immunoblots. The enzyme was only weakly recognized by polyclonal antibodies against purified spinach GK, indicating substantial differences in molecular structure of the two proteins. Highly reducing conditions stabilized GK activity and were required for activation of crude leaf enzyme. The enzyme had a broad pH optimum of 6.8–8.5, and formed 3-phosphoglycerate and ADP as reaction products. Apparent K _ms for D-glycerate and Mg-ATP were 0.11 and 0.25 mM, respectively. The enzyme was strongly affected by a number of phosphoesters, especially by 3-phosphoglycerate (K _i= 0.36 mM), fructose bisphosphates and nucleoside bisphosphates. Inhibition by 3-phosphoglycerate was competitive to Mg-ATP and noncompetitive to D-glycerate. Pyruvate was found noncompetitive to D-glycerate (K _is=4 mM). The ratio of stromal concentration of Mg-ATP to phosphoesters, particularly to 3-phosphoglycerate, may be of importance in the regulation of GK during C₄-photosynthesis.Abbreviations DEAE diethylaminoethyl - kDa kdalton - GAP-DH glyceraldehyde phosphate dehydrogenase - GK glycerate kinase - LDH lactate dehydrogenase - 2-ME 2-mercaptoethanol - M_r relative molecular mass - PEP phosphoenolpyruvate - PGA(PK) phosphoglycerate (phosphokinase) - PK pyruvate kinase - SDS-PAGE sodium dodecyl sulfatepolyacrylamide gel electrophoresis