镉胁迫对桂花生长和养分积累、分配与利用的影响

桂花(Osmanthus fragrans var.thunbergii)是长江流域镉污染地区普遍栽植兼具绿化、观赏和净化环境等重要价值的园林树种之一。为了解镉胁迫条件下桂花生长适应特性,采用盆栽试验研究了不同镉浓度处理下(CK:0mg·kg-1;I:25mg·kg-1;II:50mg·kg-1;III:100mg·kg-1;IV:200mg·kg-1)一个生长季节内一年生桂花生物量生产、生物量分配格局以及C、N、P积累、分配与利用特征。植物各器官生物量生产及C、N和P积累量均表现出随镉处理浓度的增加而降低的趋势,较高浓度镉处理(II、III、IV)明显抑制了桂花的生物量生产、C、N和P的积累,显著改变了生物量及其C、N和P积累量的分配格局,但相对较低浓度镉处理(I)对桂花生物量生产以及C、N和P的积累与分配特征影响并不显著。一定浓度的镉胁迫处理(I、II、III)表现出提高桂花N的利用效率而降低P的利用效率的趋势,但重度镉胁迫(IV)均降低了桂花N和P的利用效率。结果表明桂花具有一定的抗镉胁迫能力,但较高程度的镉胁迫显著影响了桂花生长及养分格局。     

Cd胁迫下施N对台湾桤木(Alnus formosana)干物质及N、P、K、Cd积累与分配的影响

采用盆栽试验,研究了Cd胁迫下施N对台湾桤木植株的干物质及N、P、K、Cd积累和分配的影响。结果表明:不施N条件下,Cd胁迫显著降低了台湾桤木根、茎和叶干物质积累量以及各器官N、P、K的积累量,在一定程度上降低了根和叶的N、K含量,但对根和叶的P含量均无显著影响;台湾桤木通过增加N、P、K和干物质在根中的分配比例,降低N、P、K在叶中的分配比例,以及提高N利用率(NUEN)和K利用率(NUEK)来更好地适应Cd胁迫环境;台湾桤木Cd的富集部位主要为根部,转移系数在0.06~0.22,而Cd的添加均降低了台湾桤木Cd转移系数和富集系数;30 mg·kg-1Cd胁迫下,施N在一定程度上提高了台湾桤木根、茎和叶干物质以及N、K含量和积累量,缓解了Cd胁迫所引起的对N、K吸收的限制,但对P含量和积累量无显著影响;施N提高了干物质在台湾桤木根中的分配比例和根冠比,而低N(0.4 g·kg-1)促进作用更明显;施N提高了Cd在台湾桤木茎、叶中的积累量和分配比例,而降低了其在根中的积累量和分配比例,提高了Cd转移系数(TF)和茎叶生物富集系数(BCF),显著降低了根BCF。说明施N有利于提高台湾桤木对Cd胁迫环境的适应能力。     

白刺器官间非结构性碳水化合与C：N：P计量比的关联性

为了探明荒漠生态系统优势种白刺的生存和生长策略,以便更好地服务于退化生态系统恢复及荒漠化治理。根据空气相对湿度选取阿拉善地区3个典型白刺群落样点,研究白刺根、茎、叶中非结构性碳水化合物（NSCs）的积累及分配和碳：氮：磷（C：N：P）计量比特征的变化,并分析相应区域的土壤有机质、全N、全P含量。结果表明：（1）随干旱程度加剧,白刺根、茎、叶中NSCs绝对含量减小,可溶性糖先增加后降低,淀粉先降低后增加;白刺叶片中N、P含量先增加后降低,C：N和C：P先降低后增加,在最为干旱的Plot3样点叶片N：P>16。（2）在Plot1样点,器官间根系可溶性糖显著高于茎干和叶片,根系淀粉含量显著低于茎干和叶片,在Plot3样点叶片可溶性糖含量显著高于茎干和根系,根系中淀粉含量显著高于叶片和茎干;白刺根、茎全C含量显著高于叶片,叶片N含量显著 > 根系 > 茎干;在Plot1和PLot2样点叶片P含量显著大于根系和茎干,在Plot3样点根系 > 茎干 > 叶片。（3） NSCs及构成与C：N：P计量比间关系表明叶片N、P含量与茎、叶可溶性糖含量正相关和淀粉含量负相关,根中P含量与根中淀粉含量正相关和可溶性糖含量负相关。以上结果表明,随干旱加剧白刺的生长受到水分和P的双重限制,白刺通过调整器官间NSCs积累及分配和提高N、P利用效率的策略来适应干旱生境,P含量的变化影响器官间可溶性糖和淀粉的相互转化,对NSCs构成和含量的波动起着调节作用。     

水肥耦合对谷子幼苗形态和生理指标的影响

以"晋谷21"为试验材料,采用"3414"不完全正交设计进行谷子苗期盆栽试验,研究水肥耦合对谷子幼苗形态及生理指标的影响,探索不同水分供应条件下营养元素N、P、K含量及配比与谷子抗旱性的关系。从植物生长状况、渗透调节物质、保护酶活性及MDA含量考虑,谷子在轻度(40%)水分胁迫下施用N(100、150 mg N·kg-1)、P(87、130.5mg P·kg-1)、K(249、373.5 mg K·kg-1),在重度(20%)水分胁迫下施用N(100、150mg N·kg-1)、P(87 mg P·kg-1)、K(124.5、249 mg K·kg-1)有利于植物生长;轻度与重度干旱条件下,N、P、K配合施用其交互作用效果好于单独施用N、P、K,利于谷子抗旱;重度干旱条件下,施用N、P、K虽然可以促进谷子生长、提高抗逆性,但适宜的N、P、K肥料用量范围变小,过高用量会造成生理干旱。     

岷江干旱河谷土壤水、氮和磷对小马鞍羊蹄甲幼苗生长的影响

资源阈值对植物的影响是恢复生态学的重要议题.通过近似模拟岷江干旱河谷自然干旱条件下水、氮和磷的阈值,设计析因实验,研究了一个生长季节内小马鞍羊蹄甲幼苗生长、生物生产量、资源利用效率和存活率的变化.结果表明：高水（40%田间持水量）、高磷（24 mg P·kg^-1）和低氮（100 mg N·kg^-1）处理分别促进了幼苗生长,增加了生物生产量,提高了存活率和水分利用效率,氮磷交互作用显著,水分和养分交互作用不明显.高氮（240 mg N·kg^-1）有强烈的负效应,高磷可以增大根面积、根长和根生物量,提高对氮和磷的吸收,缓解高氮的抑制作用.养分利用效率和幼苗根茎比呈显著正相关,并保持相对稳定.高水、高磷和低氮耦合有效地促进了幼苗的生长,而低水、低磷和高氮耦合则明显抑制了幼苗生长.     

白刺花幼苗对不同强度干旱胁迫的形态与生理响应

为了探讨白刺花 (Sophora davidii (Franch.) Skeels) 幼苗对持续干旱胁迫的适应能力及对策,用盆栽方法人工模拟土壤干旱条件,设置土壤田间持水量 (WHC) 100%、80%、60%、40%和20% 5个干旱胁迫处理,研究了幼苗生长、生物量分配、水分利用效率 (WUE) 、叶形态解剖结构以及光合色素等在不同干旱胁迫强度下的变化特点.结果显示,胁迫处理96d后,100% WHC条件下白刺花幼苗的总叶面积、分枝数、基径及最大根长等均最大;80% WHC对幼苗产生了轻度胁迫,随着干旱胁迫强度的进一步增加,幼苗生长显著减小.干旱胁迫限制了新生叶发生与单叶面积扩展,导致冠层总叶面积减小,从而引起幼苗光合能力及生物量积累均降低.随着胁迫强度的增加,叶生物量所占的比例及叶面积/根生物量的比值都明显减小,而根生物量所占的比例增大,这说明叶生长对干旱胁迫反应比根更加敏感.另外,干旱胁迫下WUE随着生物量与耗水量的减小而降低,表明幼苗具有浪费型水分利用对策.叶绿素 (Chla、Chlb和Chla+b) 及类胡萝卜素含量 (Car) 都随着干旱胁迫增强而呈增大趋势,但Chla/b及 Chl/Ca变化趋势相反.干旱胁迫对叶片解剖结构影响较小,土壤水分减少时仅栅栏组织厚度略有增厚,海绵组织变薄.研究结果证明,60% WHC是幼苗生长、生物量积累、WUE和光捕获复合体活性受到明显抑制的干旱胁迫强度阈值;20% WHC胁迫处理对幼苗产生了严重危害.但是在实验过程中,即使在20%WHC条件下也未出现叶片凋落及幼苗死亡,表明当年生白刺花具有较强的干旱忍受能力,幼苗通过减小地上蒸发面积、增加地下生长及叶绿素含量等多种形态与生理策略适应干旱胁迫.     

模拟增雨对白刺和油蒿幼苗化学计量特征的影响

降雨是荒漠生态系统过程和功能的最重要限制因子,荒漠植物幼苗对生长季降雨的变化极端敏感。为探讨荒漠植物对未来降雨格局变化的响应,该研究选取乌兰布和沙漠2种典型荒漠植物幼苗(白刺和油蒿)为研究对象,根据生长季内(6～9月)每次降雨量,进行不同梯度的人工模拟增雨试验(CK.自然降雨;A.增雨25%;B.增雨50%;C.增雨75%;D.增雨100%),分析白刺和油蒿幼苗C、N、P含量及化学计量特征对降雨量变化的响应。结果表明:(1)从C、N、P含量在幼苗不同器官分布来看,与CK相比,增雨显著降低了白刺幼苗茎的C含量和根的C、P含量(P0.05),在一定程度上提高了叶的C、P含量和根的N含量;而增雨处理显著增加了油蒿幼苗茎和叶的C含量(P0.05),降低了叶、根的N含量和茎、叶、根的P含量。(2)从化学计量比来看,增雨对白刺幼苗茎、叶、根的N∶P影响无显著差异,比值均大于16,且在增雨的环境下白刺幼苗相对生长率较低,主要受P元素限制;油蒿幼苗根N∶P与增雨量呈极显著负相关关系,随增雨量的增加其相对生长率增大。研究认为,模拟增雨对白刺幼苗和油蒿幼苗化学计量特征均有显著影响,但二者幼苗C、N、P元素在各器官的分配格局有所不同,增雨不利于白刺幼苗的生长,而有利于油蒿幼苗的快速生长。     

持续干旱下沙地樟子松幼苗C、N、P化学计量变化规律

为明确沙地樟子松幼苗在干旱胁迫过程中C、N和P化学计量的变化规律及分配特征,通过盆栽试验,对2年生沙地樟子松幼苗进行自然干旱处理,当土壤含水量下降到田间持水量的60%、40%、30%和20%时,测定各器官(当年生叶、一年生叶、茎、粗根和细根)的C、N和P含量。结果表明:持续干旱过程中,沙地樟子松幼苗N、P含量及C∶P和N∶P变异系数在粗根中最大,C含量变异系数在细根中最大; C、P含量及C∶P变异系数在一年生叶中最小,N含量和C∶N变异系数在当年生叶中最小,N∶P变异系数在茎中最小。随着田间持水量下降,C含量在当年生叶中先下降再上升后下降,在一年生叶、茎和粗根中先升高后降低,在细根中先下降后上升; N含量在当年生叶中先下降后上升,在一年生叶、茎和粗根中下降,在细根中先降低再升高后降低; P含量在当年生叶中上升,在一年生叶、茎、粗根和细根中先下降后上升; C∶N在一年生叶、茎、粗根和细根中增加,C∶P在当年生叶中下降,各器官N∶P均降低。相同元素在不同器官间紧密相关,而不同元素间相关性较差。因此,随着干旱加剧,沙地樟子松幼苗生长受N限制逐渐增强,N利用效率提高,各元素在叶和茎中稳定性高于粗根和细根。     

N、P、K肥对香根草修复土壤镉、锌污染效率的影响

通过盆栽试验研究在30 mg/kg镉(Cd)污染土壤条件下N[CO(NH2)2:100、200、300 mg/kg土]、P(P2O5:50、100、200 mg/kg土)和K(KCl:100、200、300 mg/kg土)处理对香根草修复土壤Cd和锌(Zn)污染效率的影响。结果表明:3种N处理能促进香根草地上部生长,而且显著提高地上部特别是叶的Cd和Zn含量,导致其修复效率成倍显著增加;200 mg/kg K处理显著提高Zn修复效率,但300 mg/kg K和50、200 mg/kg P处理却显著降低Cd、Zn修复效率。因此,为改善香根草对较贫瘠土壤中Cd、Zn污染的修复效率,应对香根草适施N肥,并控制或者不施P、K肥为佳。     

峨眉冷杉幼苗叶片功能特征及其N、P化学计量比对模拟大气氮沉降的响应

通过人工施氮模拟大气氮沉降,研究了施氮对峨眉冷杉(Abies fabiri)幼苗叶片功能特征、氮和磷含量及其化学计量比的影响,以及幼苗对氮素的积累效应。结果表明:经过2个生长季节的施氮处理(2009年和2010年,N2)幼苗的总生物量、叶干重、叶重比、叶片氮和磷含量及其N:P分别高于对照处理11.29%、46.70%、41.40%、37.30%、22.33%和6.43%,而比叶面积则降低了6.61%,其中叶干重、叶重比和叶片氮含量与对照处理差异显著(P<0.05),N:P差异极显著(P<0.01),并且叶干重与叶片氮含量具有较强的线性相关;与经1个生长季节施氮处理(2009年,N1)的幼苗总生物量、叶干重、叶重比、比叶面积、叶片氮和磷含量及其N:P的比较分析表明,除叶重比和比叶面积外,其他指标N2均高于N1;人工施氮显著促进了幼苗叶片的生长,提高了叶片氮、磷含量及其N:P,但也反映幼苗生长仍受氮素限制,同时,峨眉冷杉幼苗具有氮素积累效应。     

N deposition, N transformation and N leaching in acid forest soils

Nitrogen deposition, mineralisation, uptake and leaching were measured on a monthly basis in the field during 2 years in six forested stands on acidic soils under mountainous climate. Studies were conducted in three Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] plantations (D20: 20 year; D40: 40 yr; D60: 60 yr) on abandoned croplands in the Beaujolais Mounts; and two spruce (Picea abies Karst.) plantations (S45: 45 yr; S90: 90 yr) and an old beech (Fagus sylvatica L.) stand (B150: 150 yr) on ancient forest soils in a small catchment in the Vosges Mountains. N deposition in throughfall varied between 7–8 kg ha^–1 year^–1 (D20, B150, S45) and 15–21 kg ha^–1 yr^–1 (S90, D40, D60). N in annual litterfall varied between 20–29 kg ha^–1 (D40, D60, S90), and 36–43 kg ha^–1 (D20, S45, B150). N leaching below root depth varied among stands within a much larger range, between 1–9 kg ha^–1 yr^–1 (B150, S45, D60) and 28–66 kg ha^–1 yr^–1 (D40, S90, D20), with no simple relationship with N deposition, or N deposition minus N storage in stand biomass. N mineralisation was between 57–121 kg ha^–1 yr^–1 (S45, D40, S90) and between 176–209 kg ha^–1 yr^–1 in (B150, D60 and D20). The amounts of nitrogen annually mineralised and nitrified were positively related. Neither general soil parameters, such as pH, soil type, base saturation and C:N ratio, nor deposition in throughfall or litterfall were simply related to the intensity of mineralisation and/or nitrification. When root uptake was not allowed, nitrate leaching increased by 11 kg ha^–1 yr^–1 at S45, 36 kg ha^–1 yr^–1 at S90 and between 69 and 91 kg ha^–1 yr^–1 at D20, D40, B150 and D60, in relation to the nitrification rates of each plot. From this data set and recent data from the literature, we suggest that: high nitrification and nitrate leaching in Douglas-fir soils was likely related to the former agricultural land use. High nitrification rate but very low nitrate leaching in the old beech soil was related to intense recycling of mineralised N by beech roots. Medium nitrification and nitrate leaching in the old spruce stand was related to the average level of N deposition and to the deposition and declining health of the stand. Very low nitrification and N leaching in the young spruce stand were considered representative of fast growing spruce plantations receiving low N deposition on acidic soils of ancient coniferous forests. Consequently, we suggest that past land use and fine root cycling (which is dependent on to tree species and health) should be taken into account to explain the variability in the relation between N deposition and leaching in forests.     

Amine inversion in proteins. A 13C-NMR study of proton exchange and nitrogen inversion rates in N epsilon,N epsilon,N alpha,N alpha-[13C]tetramethyllysine,N epsilon,N epsilon,N alpha,N alpha-[13C]tetramethyllysine methyl ester, and reductively methylated concanavalin A

Exchange rates were calculated as a function of pH from line widths of methylamine resonances in 13C-NMR spectra of N epsilon,N epsilon,N alpha,N alpha-[13C]tetramethyllysine (TML) and N epsilon,N epsilon,N alpha,N alpha-tetramethyllysine methyl ester (TMLME). The pH dependence of the dimethyl alpha-amine exchange rate could be adequately described by assuming base-catalyzed chemical exchange between two diastereotopic methyl populations related by nitrogen inversion. Deprotonation of the alpha-amine was assumed to occur by proton transfer to (1) OH-, (2) water, (3) a deprotonated amine or (4) RCO2-. Microscopic rate constants characterizing each of these transfer processes (k1, k2, k3 and k4, respectively) were determined by fitting the rates calculated from line width analysis to a steady-state kinetic model. Using this procedure it was determined that for both TML and TMLME k2 approximately equal to 1-10 M-1 s-1, k3 approximately equal to 10(6) M-1 s-1 and ki, the rate constant for nitrogen inversion was about 10(8)-10(9) s-1. Upper limits of 10(12) and 10(3) M-1 s-1 could be determined for k1 and k4, respectively. A similar kinetic analysis was used to explain pH-dependent line-broadening effects observed for the N-terminal dimethylalanyl resonance in 13C-NMR spectra of concanavalin A, reductively methylated using 90% [13C]formaldehyde. From exchange data below pH 4 it could be determined that amine inversion was limited by the proton transfer rate to the solvent, with a rate constant estimated at 20 M-1 s-1. Above pH 4, exchange was limited by proton transfer to other titrating groups in the protein structure. Based upon their proximity, the carboxylate side chains of Asp-2 and Asp-218 appear to be likely candidates. The apparent first-order microscopic rate constant characterizing proton transfer to these groups was estimated to be about 1 X 10(4) s-1. Rate constants characterizing nitrogen inversion (ki), proton transfer to OH- (k1) and proton transfer to the solvent (k2) were estimated to be of the same order of magnitude as those determined for the model compounds. On the basis of our results, it is proposed that chemical exchange processes associated with base-catalyzed nitrogen inversion may contribute to 15N or 13C spin-lattice relaxation times in reductively methylated peptides or proteins.     

Determination of N6-Threoninocarbonyladenosine,N2, N2-Dimethylguanosine,Pseudouridine and Other Ribonucleosides in Human Breast Milk

Abstract

Seven modified ribonucleosides from degraded tRNA and rRNA were quantified in milk from mothers with preterm infants. The amounts of N⁶-threoninocarbonyladenosine, N², N²-dimethylguanosine and pseudouridine supplied in the milk have been estimated and related to the respective urinary amounts excreted by preterm infants.     

N,N,N-三甲基壳聚糖甲基硫酸盐的合成及理化性质的测定

壳聚糖与甲醛、甲酸反应得到N,N-二甲基壳聚糖,然后以硫酸二甲酯为季铵化试剂反应得到N,N,N-三甲基壳聚糖甲基硫酸盐(TMCMS),用IR1、H NMR和元素分析对其结构进行了表征。元素分析结果表明其季铵化度为74.6%,差示扫描量热法和热重分析法结果表明其热稳定性比壳聚糖差,但其水溶性明显优于壳聚糖,25℃时在水中的溶解度可达20 mg/mL,浓度为2 mg/mL时在pH 3～12范围内无沉淀产生。     

A synthesis of N6,N6,N6-trimethyl-L-lysine dioxalate in gram amounts

A procedure is described for the synthesis of crystalline N6,N6,N6-trimethyl-L-lysine dioxalate in gram amounts starting from the commercially available N2-tert-butoxycarbonyl-N6-benzyloxycarbonyl-L-lysine, which is reacted with methyl iodide in methanol in the presence of potassium hydrogen carbonate after deprotection of the side-chain amino group by catalytic hydrogenation. The work-up involves only filtrations and evaporations.     

Formation and stability of helical poly(N epsilon,N epsilon,N epsilon-trimethyl-L-lysine) in sodium perchlorate solution

Poly(trimethyl-L-lysine), [Lys(Me₃)]_n, is converted from random coil to α-helix at about 1/30 of the NaClO₄ concentration required by poly(L-lysine), (Lys)_n. NaClO₄ generates turbidity in [Lys(Me)₃]_n at concentrations above that required for helix formation, and decreases turbidity above lM NaClO₄. The turbidity runs parallel to enhanced, and then decreased, fluorescence of a dansyl label. Helix formation per se does not induce enhanced fluorescence. Increasing NaClO₄ concentration increases T_m linearly with log[NaClO₄] for both (Lys)_n and [Lys(Me₃)]_n until the denaturing effect of high NaClO₄ sets in. Increasing NaClO₄ also increases the breadth of the transition. Heating helical [Lys(Me₃)]_n or (Lys)_n does not produce a CD spectrum resembling that of “random-coil” (Lys)_n, except for [Lys(Me₃)]_n at relatively low NaClO₄ concentration.