Optimization and evaluation of vegetation photosynthesis and respiration model using the measurements collected from the forest site of subtropical coniferous-evergreen

 碳循环模型参数的确定和优化对生态系统净CO₂交换(NEE)的模型计算至关重要。该文利用2010–2012年ChinaFLUX千烟洲站点的通量观测资料, 对植被光合呼吸模型(VPRM)的参数进行了优化。通过比较两种不同的拟合方案, 发现利用传统光响应方程得到的参数不适用于VPRM, 而利用模型自身反演方案拟合得到的参数最大光量子效率(λ)达0.203, 大于C₃植物平均值, 但与其他相关研究结果吻合。采用VPRM模型反演方案优化得到的参数后, VPRM能较准确地模拟千烟洲站不同季节的NEE。其对全年半小时NEE模拟的平均误差为–0.86 μmol·m^–2·s^–1, 相关系数为0.72。模型可准确地模拟生长旺季NEE平均日变化, 但低估了非生长旺季白天吸收峰值约52%。通过个例分析发现, VPRM模型可以准确模拟晴天条件下NEE的时间变化, 但对阴雨天条件下NEE的模拟还存在较大的不确定性。该研究将有助于进一步改进CO₂通量及浓度的区域数值模拟。     

植被光合呼吸模型在千烟洲亚热带常绿针叶林的优化及验证

碳循环模型参数的确定和优化对生态系统净CO₂交换(NEE)的模型计算至关重要。该文利用2010-2012年ChinaFLUX千烟洲站点的通量观测资料, 对植被光合呼吸模型(VPRM)的参数进行了优化。通过比较两种不同的拟合方案, 发现利用传统光响应方程得到的参数不适用于VPRM, 而利用模型自身反演方案拟合得到的参数最大光量子效率(λ)达0.203, 大于C₃植物平均值, 但与其他相关研究结果吻合。采用VPRM模型反演方案优化得到的参数后, VPRM能较准确地模拟千烟洲站不同季节的NEE。其对全年半小时NEE模拟的平均误差为-0.86 μmol·m^-2·s^-1, 相关系数为0.72。模型可准确地模拟生长旺季NEE平均日变化, 但低估了非生长旺季白天吸收峰值约52%。通过个例分析发现, VPRM模型可以准确模拟晴天条件下NEE的时间变化, 但对阴雨天条件下NEE的模拟还存在较大的不确定性。该研究将有助于进一步改进CO₂通量及浓度的区域数值模拟。     

温带森林不同演替阶段下的土壤CO2排放通量昼间变化

采用时空替代法,在长白山北坡分别选取了红松针阔叶混交林演替序列的5个不同阶段:草地、灌木林(幼龄林)地、白桦林地、阔叶杂木林地和红松阔叶林地,进行土壤CO_2排放通量昼间变化野外同步观测研究,旨在揭示温带森林不同演替阶段下的土壤呼吸CO_2排放过程的差异,探究其与温度、湿度、土壤理化性质等环境因子的关系。结果表明:(1)温带森林不同演替阶段下的土壤CO_2排放通量具有统一性,均为大气CO_2的源,这种统一性确保了小的时段(如昼间)观测能通过换算,实现CO_2排放量的估算。(2)CO_2排放通量的昼间排放都呈现出明显的单峰型,峰值在13:00—15:00左右,草地和灌木林地的峰值大概在13:00左右,明显提前于白桦林地、阔叶杂木林地和红松阔叶林地(14:00—15:00左右)。红松阔叶林地的土壤呼吸有明显的滞后性特征,峰值在15:00左右,比其他几个样地明显推迟。(3)土壤CO_2排放通量平均值由低到高排列依次为草地(2.760μmol m~(-2)s~(-1))、灌木林地(2.854μmol m~(-2)s~(-1))、白桦林地(3.048μmol m~(-2)s~(-1))、阔叶杂木林地(3.696μmol m~(-2)s~(-1))、红松阔叶林地(4.61μmol m~(-2)s~(-1))。随着温带森林演替的正向进行,土壤CO_2排放通量依次增大,次序为草地灌木林地白桦林地阔叶杂木林地红松阔叶林地。(4)环境因子中,0—5 cm土壤温度与土壤CO_2排放通量相关系数最高,土壤温度监测对土壤CO_2排放量的估算作用明显。     

基于模型数据融合的中国温带和亚热带典型森林生态系统碳通量模拟

生态系统碳循环过程对水分响应的研究已成为全球变化关注的焦点问题之一。基于长白山温带针阔混交林与千烟洲亚热带人工针叶林观测站2003—2009年生长季的碳通量(NEE)和气象观测数据,综合考虑水分对光合、呼吸作用的影响,构建不同的NEE模型,并应用模型数据融合方法优化模型参数、遴选最适模型,系统分析了水分因子对不同森林生态系统碳循环的影响。结果表明:(1)优化后的模型参数均能被NEE实测数据较好约束。长白山生长季的光合、呼吸参数值均高于千烟洲,未考虑空气饱和水汽压差(VPD)的模型高估了千烟洲温度敏感性参数(Q10)值、低估了千烟洲基础呼吸速率参数(BR)值;(2)仅考虑VPD对光合作用影响的模型是长白山生长季碳通量模拟的最优模型,但模拟精度提高不显著。不同模型间碳通量组分模拟结果差异较小;(3)考虑VPD和土壤含水量对光合、呼吸作用共同影响的模型是千烟洲生长季碳通量模拟的最优模型,并且显著提高了模拟精度。未考虑水分的模型在生长季高估了总生态系统生产力(GEP)总量2.0%(21.85 g C/m~2),同时更大幅度地高估了生态系统呼吸(RE)总量4.4%(38.02 g C/m~2),从而导致NEE总量低估于实测值7.8%(18.55 g C/m~2)。     

川西贡嘎山峨眉冷杉成熟林生态系统CO2通量特征

成熟森林的碳收支对陆地生态系统碳循环研究具有重要意义。目前,我国关于西南亚高山暗针叶林成熟林碳通量的研究还相对较少,尚不明确对碳循环的作用。以涡度相关技术为基础,对川西贡嘎山东坡峨眉冷杉成熟林生态系统尺度的CO_2通量进行长期定位观测。利用2015年6月至2016年5月观测数据,分析了峨眉冷杉成熟林净生态系统CO_2交换量(NEE)、生态系统呼吸(Re)和总生态系统生产力(GPP)的季节变异特征及其源汇状况,并结合环境因子,分析CO_2通量的主要控制因子。结果表明:(1)峨眉冷杉成熟林NEE具有明显的日变化特征,呈现"U"形变化,白天为负值,夜间为正值,中午前后CO_2通量达到最大;各月间日平均NEE变化差异显著,NEE峰值最大出现在2015年6月(-0.64 mg CO_2m~(-2)s~(-1)),峰值最小出现在2016年1月(-0.08 mg CO_2m~(-2)s~(-1));日平均NEE由正值变为负值的时间夏季最早,冬季最晚,NEE由负值变为正值的时间冬季最早,夏季最晚。(2)峨眉冷杉成熟林NEE、Re和GPP具有明显的月变化。2015年6月和12月NEE分别达到最大值(-46.02 g C m~(-2)月~(-1))和最小值(-1.42 g C m~(-2)月~(-1));Re呈现单峰变化,最大和最小值分别出现在2015年6月(84.78 g C m~(-2)月~(-1))和2016年1月(12.82 g C m~(-2)月~(-1));GPP最大值和最小值分别出现在2015年6月(130.81 g C m~(-2)月~(-1))与2016年1月(16.15 g C m~(-2)月~(-1))。(3)空气温度(T_a)、5 cm土壤温度(T_(s5))和光合有效辐射(PAR)是影响峨眉冷杉成熟林CO_2通量的主要环境因子。T_a与CO_2通量呈指数相关(R~2=0.5283,P0.01);白天CO_2通量与PAR显著相关(R~2=0.4373,P0.01);夜晚CO_2通量与T_(s5)显著相关(R~2=0.4717,P0.01)。(4)全年NEE、Re和GPP分别为-241.87、564.81 g C m~(-2)和806.68 g C m~(-2),表明川西贡嘎山峨眉冷杉成熟林具有较强的碳汇功能。     

基于Biome-BGC模型和集合卡尔曼滤波方法的阔叶红松林生态系统水碳通量模拟

数据同化为模型与遥感观测结合提供了一条有效的途径,通过在模型运行过程中融入遥感观测数据,调整模型运行轨迹从而降低模型误差,提高模拟精度。本文利用集合卡尔曼滤波(En KF)算法同化生长季中分辨率成像光谱仪(MODIS)叶面积指数(LAI)与Biome-BGC模型模拟的LAI模拟长白山阔叶红松林的水碳通量。同时,通过改进模拟的雪面升华与土壤温度计算方法的参数,旨在降低冬季生态呼吸的模拟误差。结果表明,相对于原始模型,数据同化与模型改进后使得生态系统总初级生产力(GPP)的模拟值与观测值之间的相关系数提高0.06,中心化均方根误差(RMSE)降低0.48 g C·m~(-2)·d~(-1);生态系统呼吸(RE)的相关系数提高0.02,中心化均方根误差降低0.20 g C·m~(-2)·d~(-1);净生态系统碳交换量(NEE)相关系数提高0.35,中心化均方根误差降低0.50 g C·m~(-2)·d~(-1)。同时,数据同化对蒸散发(ET)的模拟精度没有显著影响,改进的模型提高了其相关系数。基于En KF算法的数据同化提高了长白山阔叶红松林碳通量模拟精度,对于精确估算区域碳通量有着重要的意义。     

基于东北温带落叶阔叶林通量数据的BEPS模型参数优化

控制其他参数为经验常数,利用迭代方法对主要光合作用参数最大羧化速率(V_(c max))及最大电子传递速率(J_(max))进行不同数值组合,将得到的多组模拟结果的逐日总初级生产力(GPP)分别与东北帽儿山落叶阔叶林的通量观测数据进行比较,实现对小时步长BEPSHourly模型V_(c max)和J_(max)的参数优化.结果表明:对于东北温带落叶阔叶林,当V_(c max)为41.1μmol·m~(-2)·s~(-1)、J_(max)为82.8μmol·m~(-2)·s~(-1)时,模拟的2011年逐日GPP与观测数据比较的均方根误差(RMSE)最小,为1.10 g C·m~(-2)·d~(-1),R~2最高,为0.95.经过光合作用参数V_(c max)和J_(max)优化后,BEPSHourly模型能更好地模拟GPP的季节变化.     

浙江天目山老龄森林生态系统CO_2通量特征

物种丰富的异龄老龄森林对陆地生态系统动态模型及全球碳收支具有十分重要的意义.目前,我国关于老龄森林碳通量的研究很少,亚热带地区的老龄林更鲜有报道.本研究利用涡度相关技术观测了我国中亚热带地区的浙江天目山一个老龄常绿落叶阔叶混交林生态系统的CO_2通量.以2013年7月到2014年6月的观测数据为依据,分析了此老龄林净生态系统碳交换量(NEE)、生态系统呼吸量(R_e)、生态系统总交换量(GEE)的变化.结果表明:研究期间老龄林常绿落叶阔叶混交林生态系统NEE月总量除12、2月为正值外(表现为碳源),其余月份均为负值(表现为碳汇).NEE月总量平均为-61.52 g C·m~(-2),各月碳吸收量以6月(-149.40 g C·m~(-2))最高,10月次之,呈双峰变化;最大碳源出现在2月(23.45g C·m~(-2)).各月NEE平均日变化差异明显,6月的平均通量峰值最大,达到-0.98 mg·m~(-2)·s~(-1),12月最小,为-0.35mg·m~(-2)·s~(-1);NEE符号改变的时间也呈明显的季节变化特征;全年NEE、R_e、GEE分别为-738.18、931.05、-1669.23g C·m~(-2).与相近纬度相近林型的其他森林生态系统相比,由于其复层结构和多种幼龄更新树木的存在,其测定的固碳量较大.表明我国中亚热带天目山地区的老龄森林生态系统不是处于碳收支稳定状态,而是具有相对较高的固碳能力.     

沙质草地生长季生态系统碳净交换量特征及土壤呼吸贡献率

以科尔沁沙质草地为研究对象,利用开路涡度相关系统和LI-8150土壤呼吸自动观测系统,分析了生长季生态系统二氧化碳(CO_2)净交换量(NEE)的变化特征,土壤呼吸(R_s)对生态系统呼吸(R_(eco))的贡献率,以及生态系统总初级生产力(GPP)的大小。结果表明:生长季NEE存在明显的月均日变化特征,总体呈单峰型,其中7月的日变化最为明显,NEE月均日最大吸收速率(-5.62μmol·m~(-2)·s~(-1))和最大释放速率(3.14μmol·m~(-2)·s~(-1))均出现在7月份;生长季内生态系统总体表现为碳汇,固碳量为25.85 g C·m~(-2);R_s对R_(eco)的贡献率为78.39%,R_(eco)对GPP的贡献率为90.62%,生长季内GPP总累积量为275.51g C·m~(-2)。     

基于模型数据融合的千烟洲亚热带人工林碳水通量模拟

人工林生态系统是我国森林生态系统的重要组成部分,在全球碳平衡中的作用越来越受到重视.利用千烟洲亚热带人工针叶林通量观测站的碳水通量和气象观测数据,通过模型数据融合方法对碳水循环过程模型——SIPNET模型关键参数进行反演,模拟了2004-2009年千烟洲人工林生态系统的碳水通量.结果表明:仅用碳通量观测数据优化模型参数时,净生态系统碳交换量(NEE)模拟效果较好(R2=0.934),而生态系统蒸散(ET)模拟效果较差(R2=0.188);同时用碳水通量观测数据优化时,NEE模拟效果稍差(R2=0.929),但ET模拟效果显著提升(R2=0.824),说明利用碳水通量观测数据同时优化,SIPNET模型才能较好地模拟试验站点碳水通量.在此基础上,开展了人工林生态系统碳通量对降水变化响应的敏感性分析,发现降水量减少对光合作用的影响比对呼吸作用的影响更为强烈,且碳水通量同时参与优化时模型才能较好地模拟碳通量随降水减少而快速降低的趋势,表明如果不能同时利用碳水通量进行参数优化,模型无法正确揭示生态系统碳循环对降水变异的响应.     

Distribution of polyamines and their related catabolic enzyme in etiolated and light-grown leguminosae seedlings

Diamine-oxidase (DAO; EC 1.4.3.6) activity and di-and polyamine levels were estimated along the epicotyl and root of light-grown and etiolated lentil (Lens culinaris Medicus) and pea (Pisum sativum L.) seedlings. The activity of DAO was higher in etiolated epicotyls than in lightgrown ones. In both species there was a positive correlation between DAO activity and the diamine (putrescine and cadaverine) levels along the whole epicotyl and root. Polyamine (spermine and spermidine) distribution seemed to be associated with the meristematic and elongating zone of the epicotyl and root. The physiological function of DAO is discussed in relation to its possible role in providing hydrogen peroxide to peroxidase-dependent reactions occurring in the cell wall.Abbreviations CAD cadaverine - DA diamine - DAO diamine oxidase - PA polyamine - PUT putrescine - SPD spermidine - SPM spermine     

The relationship between the redox state of Q A and photosynthesis in leaves at various carbon-dioxide,oxygen and light regimes

The response of chlorophyll fluorescence elicited by a low-fluence-rate modulated measuring beam to actinic light and to superimposed 1-s pulses from a high-fluence-rate light source was used to measure the redox state of the primary acceptor Q _A of photosystem II in leaves which were photosynthesizing under steady-state conditions. The leaves were exposed to various O₂ and CO₂ concentrations and to different energy fluence rates of actinic light to assess the relationship between rates of photosynthesis and the redox state of Q _A. Both at low and high fluence rates, the redox state of Q _A was little altered when the CO₂ concentration was reduced from saturation to about 600 l·l^-1 although photosynthesis was decreased particularly at high fluence rates. Upon further reduction in CO₂ content the amount of reduced Q _A increased appreciably even at low fluence rates where light limited CO₂ reduction. Both in the presence and in the absence of CO₂, a more reduced Q _A was observed when the O₂ concentration was below 2%. Q _A was almost fully reduced when leaves were exposed to high fluence rates under nitrogen. Even at low fluence rates, Q _A was more reduced in shade leaves of Asarum europaeum and Fagus sylvatica than in leaves of Helianthus annuus and Fagus sylvatica grown under high light. Also, in shade leaves the redox state of Q _A changed more during a transition from air containing 350 l·l^-1 CO₂ to CO₂-free air than in sun leaves. The results are discussed with respect to the energy status and the CO₂-fixation rate of the leaves.Abbreviations and symbols L 1,2 first and second actinic light beam - Q _A primary acceptor of photosystem II - q _Q Q-quenching     

An evaluation of light and CO2 limitation of leaf photosynthesis by CO2 gas-exchange analysis

Numerical values which define the relative limitation of photosynthesis by light and CO₂ were computed from the slopes of light-and CO₂-response curves of photosynthesis. This method offers an easy approach for the characterization of photosynthesis of leaves.     

Limitations of direct estradiol and testosterone immunoassay kits

Estradiol (E2) and testosterone (T) are biologically active hormones that serve as important diagnostic markers in serum of premenopausal and postmenopausal women and in men. These hormones are measured frequently by immunoassay in clinical laboratories and the test results are used in the diagnosis and treatment of patients. For measuring the hormones by immunoassay, most laboratories utilize commercially available reagents that are packaged in the form of a kit and are used either in an automated instrument or manually. However, both the diagnostic kit manufacturer and testing laboratory seldom thoroughly validate the assay methods generated with these kits. This deficiency may lead to unreliable test results that could affect clinical evaluation and treatment of patients. The purpose of the present study was to assess the reliability of immunoassays that quantify serum E2 and T levels with commercial diagnostic kits. The data generally show wide differences in the apparent levels of each hormone in a given sample obtained with kits from different manufacturers. This was especially true when measuring postmenopausal E2 and T levels. However, a purification step, which included organic solvent extraction, prior to radioimmunoassay (RIA) of E2 gave values that compared well with those obtained by conventional RIA (with preceding extraction/chromatographic steps). Our results point out the importance of more thoroughly validating assays performed with commercial immunoassay kits, especially with respect to sensitivity and specificity, prior to their use for measuring hormone levels in patient samples.     

Light-induced pH changes in leaves of C4 plants

Light-induced changes in the fluorescence of the pH-indicating dyes pyranine or 5-(and 6-)carboxy-2, 7-dichlorofluorescein (CDCF) which had been fed to leaves were examined to monitor cellular pH changes. After short-term feeding of pyranine (pK 7.3) to leaves of Amaranthus caudatus L., a NAD-malic-enzyme-type C₄ plant, vascular bundles and surrounding cells became fluorescent. Fluorescence emission from mesophyll cells required longer feeding times. In CO₂-free air, pyranine fluorescence increased much more on illumination after mesophyll cells had become fluorescent than when only the vascular bundles and the bundle sheath of Amaranthus leaves had been stained. After short feeding times and in the absence of actinic illumination, CO₂ decreased pyranine fluorescence very slowly in Amaranthus and rapidly in C₃ leaves. After prolonged feeding times, the extent of the light-dependent increase in pyranine fluorescence was several times greater in different C₄ plants than in C₃ species. The kinetics of the fluorescence changes were also remarkably different in C₃ and C₄ plants. Carbon dioxide (500 l · l^–1) suppressed the light-induced increase in pyranine fluorescence more in C₄ than in C₃ leaves. Light-dependent changes in light scattering, which are indicative of chloroplast energization, and in 410-nm transmission, which indicate chloroplast movement, differed kinetically from those of the changes in pyranine fluorescence. Available evidence indicated that light-dependent changes in pyranine fluorescence did not originate from the apoplast of leaf cells. Microscopic observation led to the conclusion that, after prolonged feeding times or prolonged incubation, changes in pyranine fluorescence emitted from C₄ leaves reflect pH changes mainly in the cytosol of mesophyll cells. A transient acidification reaction indicated by quenching of pyranine fluorescence in the dark-light transient and not observed in C₃ species is attributed to the carboxylation of phosphoenolpyruvate. After short feeding times and in the absence of actinic illumination, CO₂ (250 l l^–1) decreased pyranine fluorescence very slowly in Amaranthus and more rapidly in C₃ leaves. After prolonged feeding times, both the rate and the extent of CO₂-dependent quenching of pyranine fluorescence increased, but the increase was insufficient to indicate the presence of highly active carbonic anhydrase in the compartment from which pyranine fluorescence was emitted. In contrast to pyranine, CDCF (pK 4.8) did not increase but rather decreased its fluorescence on illumination of an Amaranthus leaf, indicating acidification of an acidic compartment, most probably the vacuole of green leaf cells. The pattern of the acidification reaction was similar in C₄ and C₃ leaves. The remarkably large extent of the light-dependent increase in pyranine fluorescence from leaves of C₄ species and its slow kinetics are proposed to be caused by an alkalization of the cytosol which in the absence of CO₂ is larger in the mesophyll than in the bundle sheath. It gives rise to deprotonation of dye originally located in the mesophyll and, in addition, of dye which diffuses from the bundle sheath into the mesophyll following a pH gradient. Implications of slow diffusional transport of pyranine and CO₂ between mesophyll and bundle-sheath cells and the fast metabolite transport required in C₄ photosynthesis are discussed.Abbreviations CDCF 5-(and 6-)carboxy-2,7-dichlorofluorescein - DHAP dihydroxyacetone phosphate - PGA 3-phosphoglycerate This work was supported by the Sonderforschungsbereiche 176 and 251 of the University of Würzburg and by the Gottfried-Wilhelm-Leibniz Program of the Deutsche Forschungsgemeinschaft. A.S.R. was the recipient of a fellowship of the Alexander-von-Humboldt Foundation. We are grateful to Mrs. S. Neimanis for cooperation.     

Light-dependent pH changes in leaves of C4 plants Comparison of the pH response to carbon dioxide and oxygen with that of C3 plants

Cytosolic and vacuolar pH changes caused by illumination or a changed composition of the gas phase were monitored in leaves of the NAD malic-enzyme-type C₄ plant Amaranthus caudatus L. and the C₃ plant Vicia faba L. by recording changes in the fluorescence of pH-indicating dyes which had been fed to the leaves. Light-dependent cytosolic alkalization and vacuolar acidification were maximal in the mesophyll cells under high-fluence-rate illumination and in the absence of CO₂. Under the same conditions, measurements of light scattering and electrochromic absorption changes at 518 nm revealed maximum thylakoid energization. The results show an intimate relationship between the energization of the photosynthetic apparatus by light, an increase in cytosolic pH and a decrease in vacuolar pH. This was true for both the C₄ and the C₃ plant, although kinetics, extent and even direction of cytosolic pH changes differed considerably in these plants, reflecting the differences in photosynthetic carbon metabolism. Darkening produced rapid acidification in Vicia, but not in Amaranthus. Continued alkalization in Amaranthus is interpreted to be the result of the decarboxylation of a C₄ intermediate and the release of liberated CO₂. In the presence of CO₂, energy consumption by carbon reduction decreased thylakoid energization, cytosolic alkalization and vacuolar acidification. Under low-fluence-rate illumination, thylakoid energization and light-dependent cytosolic and vacuolar pH changes were decreased in CO₂-free air compared with thylakoid energization and pH changes in 1% oxygen/99% nitrogen not only in the C₃ plant, but also in Amaranthus. Since oxygenation of ribulose bisphosphate initiates energy-consuming photorespiratory reactions in 21% oxygen, but not in 1% oxygen, this shows that photorespiratory reactions are active not only in the C₃ but also in the C₄ plant in the absence of external CO₂. Photorespiratory conditions appeared to decrease energization not only in the chloroplasts, but also in the cytosol. This is indicated by decreased transfer of protons from the cytosol into the vacuole, a process which is energy-dependent.Abbreviations CDCF 5-(and 6-)carboxy-2,7-dichlorofluorescein - P₇₀₀ electron-donor pigment in the reaction center of photosystem I - RuBP ribulose-1,5-bisphosphate This work was supported, within the framework of the Sonderforschungsbereiche 176 and 251 of the University of Würzburg, by the Gottfried-Wilhelm-Leibniz Program of the Deutsche Forschungsgemeinschaft. A.S.R. was the recipient of a fellowship from the Alexander-von-Humboldt-Foundation. We are grateful to Mr. Carsten Werner and Mrs. Spidola Neimanis for cooperation.     

Acquisition and assimilation of gaseous ammonia as revealed by intracellular pH changes in leaves of higher plants

Atmospheric ammonia (NH₃) from various anthropogenic sources has become a serious problem for natural vegetation. Ammonia not only causes changes in plant nitrogen metabolism, but also affects the acid-base balance of plants. Using the pH-sensitive fluorescent dyes pyranine and esculin, cytosolic and vacuolar pH changes were measured in leaves of C₃ and C₄ plants exposed for brief periods to concentrations of NH₃ in air ranging from 1.33 to 8.29 mol NH₃ · mol^-1 gas (0.94–5.86 mg · m^-3). After a lag phase, uptake of NH₃ from air at a rate of 200 nmol NH₃ · m ^{- 2} leaf area · s^{- 1} into leaves of Zea mays L. increased pyranine fluorescence indicating cytosolic alkalinisation. The increase was much larger in the dark than in the light. In illuminated leaves of the C₃ plant Pelargonium zonale L. and the C₄ plants Z. mays and Amaranthus caudatus L., NH₃-dependent cytosolic alkalinisation was particularly pronounced when CO₂ was supplied at very low levels (16 or 20 mol CO₂ · mol^{- 1} gas, containing 210 mmol O₂ · mol^{- 1} gas). An increase in esculin fluorescence, which was smaller than that of pyranine, was indicative of trapping of some of the NH₃ in the vacuoles of leaves of Spinacia oleracea L. and Z. mays. Photosynthesis and transpiration remained unchanged during exposure of illuminated leaves to NH₃, yielding an influx of 200 nmol NH₃ · m^-2 leaf area · s^-1 for up to 30 min, the longest exposure time used. Both CO₂ and O₂ influenced the extent of cytosolic alkalinisation. At 500 mol CO₂ · mol^-1 gas the cytosolic alkalinisation was suppressed more than at 16 or 20 mol CO₂ · mol^-1 gas. The suppressing effect of CO₂ on the NH₃induced alkalinisation was larger in illuminated leaves of the C₄ plants Z. mays and A. caudatus than in leaves of the C₃ plant P. zonale. A reduction of the O₂ concentration from 210 to 10 mmol O₂ · mol ^-1 gas, which inhibits photorespiration, increased the NH₃induced cytosolic alkalinisation in C₃ plants. Suppression by CO₂ or O₂ of the alkaline pH shift caused by the dissolution and protonation of NH₃ in queous leaf compartments, and possibly by the production of organic compounds synthesised from atmospheric NH₃, indicates that NH₃ which enters leaves is rapidly assimilated if photosynthesis or photorespiration provide nitrogen acceptor molecules.This work was supported by the Biotechnology and Biological Sciences Research Council and the Deutsche Forschungsgemein-schaft within the framework of the research of Sonderforschun-gsbreich 251 of the University of Würzburg. We are grateful to Dr. B. Wollenweber (The Royal Veterinary and Agricultural University, Denmark) for discussions.     

Preparation of low-molecular-weight and high-sulfate-content chitosans under microwave radiation and their potential antioxidant activity in vitro

In the present paper microwave radiation has been used to introduce N-sulfo and O-sulfo groups into chitosan with a high degree of substitution and low-molecular weight. The sulfation of chitosan was performed in microwave ovens. It was found that microwave heating is a convenient way to obtain a wide range of products of different degrees of substitution and molecular weight only by changing reaction time or/and radiation power. Moreover, microwave radiation accelerated the degradation of sulfated chitosan, and the molecular weight of sulfated chitosan was considerably lower than that obtained by traditional heating. There are no differences in the chemical structure of sulfated chitosan obtained by microwave and by conventional technology. FTIR and 13C NMR spectral analyses demonstrated that a significantly shorter time is required to obtain a satisfactory degree of substitution and molecular weight by microwave radiation than by conventional technology. In this present paper, we also determined antioxidant activity of low-molecular-weight and high-sulfate-content chitosans (LCTS). The results showed LCTS could scavenge superoxide and hydroxyl radical. Its IC50 is 0.025 and 1.32 mg/mL, respectively. It is a potential antioxidant in vitro.     

Isolation of GIF from porcine brain and studies of its zinc transfer kinetics with apo-carbonic anhydrase

Neuronal growth inhibitory factor (GIF) of porcine brain, was isolated and purified by a similar procedure which was used on the isolation of human and bovine GIF. The native porcine protein with stoichiometry of 4Cu⁺, 3Zn²⁺ was obtained for the first time. The kinetics of zinc transfer from Cu₄Zn₃MT-3 to apo-carbonic anhydrase were studied, and zinc transfer rate constants and thermodynamic parameters were obtained. It is found that like other MTs, porcine Cu₄Zn₃MT-3 can also transfer its zinc atom to apoCA, even much easier than other MTs. A possible association mechanism has been proposed, the formation of Cu₄Zn₃MT3-apoCA complex may be the rate-determining step. The obtained data indicate besides its neuronal growth inhibitory function, GIF might play a role in cellular Zn homeostasis in brain.