土壤和叶面Pb污染对小麦生长及体内Pb分布和积累的影响

通过土壤添加Pb和叶面喷施Pb溶液的方式研究了Pb污染对小麦(Triticum aestivum L. )地上部分和籽粒干质量的影响,并对Pb污染条件下小麦体内Pb的分布和积累规律以及Pb污染浓度与籽粒Pb含量的相关性、叶片Pb含量与籽粒Pb含量的相关性进行了分析.结果表明:土壤中Pb添加量为2 000 mg·kg-1时,小麦地上部分和籽粒的干质量分别较对照下降了15.5%和13.3%,差异显著(P<0.05);叶面喷施100 mg·L-1Pb溶液,小麦地上部分和籽粒干质量分别较对照下降了10.3%和15.5%,差异显著(P<0.05).在土壤和叶面Pb污染条件下,小麦各器官的Pb含量均随Pb污染浓度的提高而增大;在土壤Pb污染条件下,小麦根中的Pb含量远高于其他器官,籽粒中的Pb含量最低;在叶面Pb污染条件下,小麦叶片中的Pb含量远高于其他器官,籽粒和根中的Pb含量较低.回归分析结果表明,小麦籽粒中的Pb含量与Pb污染浓度呈极显著正相关(P<0.001),籽粒中的Pb含量与土壤Pb总含量和叶面Pb污染浓度的曲线方程分别为: y＝0.269+0.001 05x+2.736×10-7x2-1.707×10-10x3和y＝0.465+0.013x-1.1×10-5x2+3.96×10-9x3;土壤中总的Pb毒性临界值为209.3 mg·kg-1,叶面Pb的毒性临界值为2.6 mg·L-1;在土壤和叶面Pb污染条件下,小麦籽粒中的Pb含量与叶片Pb含量间呈极显著的正相关(P<0.01),回归方程分别为:y=0.120 1x+0.076和y=0.001 6x+ 0.601 1,据此,在土壤和大气Pb污染条件下,可通过测定小麦叶片的Pb含量预测小麦籽粒中的Pb含量.     

水稻不同品种对铅吸收、分配的差异及机理

为探究水稻不同品种对Pb吸收积累的差异及机理,以20个不同基因型水稻品种(系)为材料,采用盆栽方法,研究了Pb在水稻植株各器官中的分配及在籽粒中的分布．结果表明,不同品种间,Pb积累量存在显著差异,但品种间的这种差异与品种类型关系不明显;不同器官、不同生育时期,Pb积累量和积累速率不同;各器官Pb浓度按根、茎、叶、穗、籽粒的顺序大幅度下降,分配到籽粒中的Pb比例很低;根与茎,茎与叶片、穗(抽穗期)、籽粒Pb含量呈极显著负相关;根与叶、穗(抽穗期)、籽粒,叶与穗(抽穗期)、籽粒的Pb含量呈正相关,相关性大多达极显著或显著水平;不同品种抽穗期叶片与成熟期籽粒间的Pb含量达显著正相关;Pb在稻米加工各产物中的分布很不均匀,稻谷经脱壳及精加工1次(2min)后,精米Pb含量仅为籽粒总含Pb量的32．88％．     

大气CO2浓度升高对玉米非结构性碳水化合物和籽粒品质的影响

本试验利用改进的开顶式气室(OTC)在黄土高原长武农业生态试验站田间模拟大气CO₂浓度升高环境,设置3个处理:CK(田间环境,自然大气CO₂浓度)、OTC(OTC气室,自然大气CO₂浓度)、OTC_e(OTC气室,CO₂浓度700 μmol·mol^-1),探讨春玉米在不同生育期各器官非结构性碳水化合物(NSC)及籽粒品质(可溶性糖、淀粉和粗蛋白)对大气CO₂浓度升高的响应,为揭示旱作区春玉米对大气CO₂浓度升高的适应机理提供科学依据。结果表明: 大气CO₂浓度升高对玉米NSC含量、积累量的影响因器官和生育期不同而异。与CK和OTC相比,OTC_e促进了生殖生长阶段叶、茎和根NSC的活化再分配,提高了叶片、茎秆和根系NSC转运到籽粒的量(ATM_NSC)、向籽粒的转运率(AR_NSC)以及对籽粒的贡献率(AC_NSC);与CK相比,OTC带来的增温效应抑制了茎和根NSC的活化再分配,促进了叶NSC的活化再分配,显著提高了玉米叶ATM_NSC、AR_NSC、AC_NSC。在两年试验中,大气CO₂浓度升高对玉米籽粒可溶性糖、淀粉和粗蛋白含量无显著影响。     

大气-土壤-小麦生态系统中铅的分布和迁移规律研究

研究铅在国道附近大气－土壤－小麦生态系统中的分布及其迁移规律。结果表明,大气中铅浓度与汽车流量成正比,而与风速、温度等相关性不明显;距公路越远,土壤及小麦中铅的含量越高,含是与距离呈一定的匀相关性,５ｍ及６０ｍ为其转折点;铅在土壤中由上上及在小麦体中由根向茎、穗的迁移较小;小麦各器官中铅含量大小依次为根〉叶〉穗〉茎〉籽。叶片、穗尚从大气中直接部分铅。在小麦不同生长阶段中,各器官积累铅量不同,其积累     

铅胁迫下三叶鬼针草内源一氧化氮的生成及其对氧化损伤的缓解效应

对不同浓度铅(Pb)胁迫下三叶鬼针草(Bidens pilosa L.)叶、茎和根中内源一氧化氮(NO)和活性氧(ROS)的生成机制及根系活力的变化,内源NO对Pb胁迫下三叶鬼针草幼苗氧化损伤的缓解效应进行了研究。结果显示,在0~1000 mg/L范围内,随着Pb浓度的增加,叶片中NO含量呈升高趋势,根中NO含量呈先升高后降低的趋势,但仍高于对照,Pb浓度在0~400 mg/L范围内,茎中NO含量与对照持平,Pb浓度大于600 mg/L时,茎中NO含量低于对照;600 mg/L Pb处理能显著增强叶、茎和根中一氧化氮合成酶(NOS)和硝酸还原酶(NR)活性,显著增加叶和茎中亚硝酸根离子(NO_2~-)和类胡萝卜素(Car)含量,NOS、NR、NO_2~-和Car均能促进叶片中内源NO的生成,NOS是根中内源NO生成的主要途径。Pb胁迫使超氧阴离子(O_2~(·-))产生速率、过氧化氢(H_2O_2)含量、丙二醛(MDA)含量和相对电导率(REC)显著升高,从而造成幼苗严重的膜脂过氧化损伤,而胁迫诱发产生的NO能降低根中ROS的产生,促进幼苗根系活力,进而缓解胁迫造成的膜脂过氧化损伤。     

不同Hg浓度下水稻中Hg的分布累积特征

利用土壤盆栽实验方法,研究了土壤中Hg的形态分布,以及不同Hg浓度下,水稻不同生长时期各组织中Hg的分布规律和累积特征.土壤Hg存在的形态为:有机结合态＞残渣态＞＞氧化态＞＞溶解与可交换态≈特殊吸附态,在水稻的生长过程中,土壤中的Hg呈现从残渣态向有机结合态转化的趋势,有机结合态Hg平均占比为61.7％,是土壤Hg最重要的存在形态.Hg在水稻不同部位的浓度分布呈现W根＞W叶＞W茎＞W穗＞W籽粒,分析表明,水稻根、茎和籽粒中的Hg与土壤各形态Hg浓度呈显著或极显著正相关,但在水稻生长后期叶片中Hg与土壤Hg浓度的相关性不显著,叶片Hg与大气Hg进行交换起主要作用,改变了累积状况.随着土壤Hg浓度的增加和生长期的延长,根对Hg的束缚能力逐渐增加,根部Hg累积量增大,所占比例上升,而茎和叶的累积量相对稳定.     

玉米重金属铅(Pb~(2+))含量的配合力分析与育种对策

选择有代表性的12个玉米自交系,按Griffing4模式组配获得66个组合(F1),用温室盆栽,在3个Pb2+污染水平下对叶片和子粒Pb2+含量配合力和遗传参数进行分析。结果表明:玉米叶片和子粒的Pb2+含量一般配合力与特殊配合力差异均达到显著水平,非加性方差大于加性方差,遗传方差大于环境方差,广义遗传率大于狭义遗传率,该性状的变异主要来自遗传因素,遗传力较强。玉米种质筛选过程中,土壤Pb2+浓度在333.32 mg/kg以下,用亲本郑58组配的组合在筛选时不仅注重子粒Pb2+含量未超标而且要注重叶片Pb2+高富集,其主要是兼顾饲料和粮食安全的同时进行土壤Pb2+污染的生物修复;土壤Pb2+浓度高于715.46 mg/kg时,用亲本178组配的组合筛选应注意叶片和子粒低Pb2+积累的种质选育,对今后在不同Pb2+污染土壤中开展玉米品种筛选和规避污染育种策略的选择具有一定的指导意义。     

绿色食品生产中土壤作物系统铅的积累与迁移研究

研究了Pb在土壤-作物生态系统中的积累和迁移,并结合水稻绿色食品生产,进行了无机肥、有机肥和生物菌肥及其配比试验．结果表明,土壤全Pb含量随土层的加深而逐渐递减,收获后土壤全Pb含量在0～15和15～30cm分别为11．14和9．37mg·kg^-1．水稻根从土壤中吸收Pb,并向茎、叶和籽粒中迁移．在同一生长期,水稻植株不同部位全Pb累积态势为：根>茎叶>籽粒．在不同生长期,随水稻生长发育,全Pb含量缓慢增加,至收获时,606—14和辽粳294籽粒中全Pb含量分别为0．008和0．007mg·kg^-1,均低于绿色食品标准．方差分析表明,品种间产量差异显著;不同处理间产量差异不显著．试验结果表明。可以用有机肥或生物菌肥来代替无机肥进行水稻生产．     

不同铅水平下紫茎泽兰细胞内铅的分布和化学形态的分析

该研究运用差速离心法和化学试剂逐步提取法,分析了重金属铅在紫茎泽兰亚细胞内的分布和主要化学形态。结果表明:随着Pb浓度的升高,紫茎泽兰的叶、根、茎中各亚细胞组分Pb含量逐渐增加;紫茎泽兰中的Pb在叶片分布于可溶性部分和细胞壁中,两者占总量的75.34%~84.63%;茎也主要分布于可溶性部分和细胞壁中,占总量的36.10%~57.14%和20.07%~36.52%;而在根中则富集于细胞壁和可溶性部分,分别占39.2%~49.78%和28.27%~37.62%,其他细胞器中的Pb含量均较少。紫茎泽兰叶中的Pb以盐酸提取态和水提取态为主,两者占总量的58.74%~73.04%;茎中的Pb以醋酸提取态和氯化钠提取态为主;而根中的Pb则以醋酸提取态和盐酸提取态占优势,两者占总量的39.15%~52.91%。     

不同有机肥配施对小麦和燕麦镉积累、分配及转运的影响

为探讨化肥减量配施不同有机肥对小麦和燕麦镉吸收变化特征。试验在化肥施用减量20%基础上,设厩肥30000 kg/hm2（AM）、生物有机肥600 kg/hm2（BF）、厩肥30000 kg/hm2+生物有机肥600 kg/hm2（AM+BF）及化肥正常施用量（CK）4个施肥处理,研究不同有机肥对作物镉积累、分配、转运影响。结果显示,有机肥配施可降低作物各器官镉吸收,与CK相比,小麦籽粒镉含量降低15.79%-36.84%,籽粒富集系数降低8.02%-24.55%,根、茎、叶、穗向籽粒的转运系数降低5.79%-56.28%;与CK相比,燕麦籽粒镉含量降低11.76%-47.06%%;处理BF、AM+BF籽粒富集系数降低38.46%、30.77%%;根、茎、叶、穗向籽粒的转运系数降低16.2%-32.77%;并且灌浆后燕麦籽粒镉含量上升伴随着茎镉含量下降。有机肥配施处理下两种作物生物量增加6.78%-11.00%;燕麦抽穗后各器官镉向籽粒的转移量、转移率、贡献率均以茎为最高。上述结果表明,配施有机肥可降低作物籽粒镉含量、富集系数和转运系数,可提高农产品安全质量,且对燕麦籽粒降镉效果优于小麦,研究发现作物抽穗后镉从茎向籽粒转运是籽粒镉积累的主要来源。     

Root growth responses to lead in young maize seedlings

This work was undertaken to follow the appearance and development of symptoms of lead toxicity in growing roots of seedlings. The effects of lead nitrate (10^-2–10⁵ M) were studied on the roots of maize (Zea mays) seedlings, cvs. Diamant and Sterling. The roots were grown on filter paper either on glass in trays or in large Petri dishes. The following characteristics of root growth were studied: seed germination, length of primary and seminal roots, number of seminal and lateral roots, length of branching zone, length of meristem and fully-elongated cells and the number of fully-elongated cells along the daily length increment. 10^-2 M lead nitrate exerted a clear toxic effect on root elongation just after radicle emergence; its influence on shoot growth was weak. However 10^-2 M Pb solution did not affect either radicle emergence itself or seminal root emergence, which can be explained by the impermeability of seed testa to lead salt. The inhibitory effect of 10^-3 M lead nitrate appeared a day later and was not as toxic: the growth of primary and seminal roots proceeded at lower rate due to a partial inhibition of cell division and cell elongation in them. 10^-3 M lead nitrate modified the root system morphology: it exerted no effect on the emergence of lateral roots and their number, but induced a more compact distribution of lateral roots along a shorter branching zone due to a reduced length of mature cells in the primary root. As a result of the more prominent inhibition of primary root growth, a shorter branching zone with more compactly located lateral roots occupied a position much closer to the root tip than in roots grown without the influence of lead.     

Removal of lead from aqueous solutions by agricultural waste maize bran

Maize bran is a low cost biosorbent that has been used for the removal of lead(II) from an aqueous solution. The effects of various parameters such as contact time, adsorbate concentration, pH of the medium and temperature were examined. Optimum removal at 20 degrees C was found to be 98.4% at pH 6.5, with an initial Pb(II) concentration of 100 mg l(-1). Dynamics of the sorption process and mass transfer of Pb(II) to maize bran were investigated and the values of rate constant of adsorption, rate constant of intraparticle diffusion and the mass transfer coefficients were calculated. Different thermodynamic parameters viz., changes in standard free energy, enthalpy and entropy were evaluated and it was found that the reaction was spontaneous and exothermic in nature. The adsorption data fitted the Langmuir isotherm. A generalized empirical model was proposed for the kinetics at different initial concentrations. The data were subjected to multiple regression analysis and a model was developed to predict the removal of Pb(II) from an aqueous solution.     

A crop tolerating oxidative stress induced by excess lead: maize

Two 14-day-old seedlings of maize (Zea mays L.) cultivars (3223 and Vero) were exposed to different concentrations of lead [0, 2, 5 and 8 mM Pb(NO₃)₂·4H₂O] for 8 days. Exposure of maize cultivars to excess Pb resulted in a significant root growth inhibition though shoot growth and absolute water content remained less affected. The results of chlorophyll a fluorescence indicated that the highly toxic Pb level affected photochemical efficiency in 3223, while no significant effect was observed in the Vero. At the highly toxic Pb concentration, higher membrane leakage was observed in 3223 leaves than that of Vero. This result was related to the accumulation of Pb. On the other hand, the results suggested that there were similar responses in total soluble POD and GR activities with increasing Pb concentrations between both cultivars. But APX activity significantly decreased at highly toxic Pb level in the Vero while a significant increase observed in the 3223. However, SOD activity in 3223 significantly decreased at the highly toxic Pb concentration compared with that at 2 mM Pb concentration. The results of the present study indicated that, Vero withstands excess Pb with its higher Pb accumulation capacity in roots and better upregulated protective mechanisms compared to 3223. Therefore, Vero is more tolerant to Pb toxicity compared to 3223 which was found to be a less tolerant cultivar.     

The isomerization of glutamate dehydrogenase in response to lead toxicity in maize

Maize (Zea mays) was cultivated on lead-adultrated soil up to 600 mg(Pb) kg-1. At maturity, the maize seeds were harvested. The glutamate dehydrogenase (GDH) was fractionated to its isoenzyme population by Rotofor isoelectric focusing (IEF). The increasing Pb concentration progressively enhanced the more acidic isoenzymes (pI 6.3 - 6.5), and at the same time suppressed the less acidic isoenzymes (pI 7.3 - 7.8) and at the 600 mg(Pb) kg-1(soil) only the most acidic couple of isoenzymes (pI 6.3, and 6.5) were detectable. The NH4+ Km values of the GDH increased progressively from 6.2 in the control to 100 mM and the total glutathione content of maize seeds from 60 to 240 nmol g-1 in the 600 mg(Pb) kg-1(soil) treated maize. The orderly, and sequential isomerization of GDH in response to Pb suggests that the enzyme functions as a sensor in the monitoring of environmentally induced stress. This revised version was published online in August 2006 with corrections to the Cover Date.     

Dose effect of cyanidin interaction with lead ions in roots of maize seedlings

The dose effect of cyanidin interaction with lead ions in maize seedling roots was established using reflectance spectroscopy and colorimetry. It was demonstrated basing on the regression analysis that changes of spectral parameters were related to enhanced complex formation when the metal concentration increases.     

The effects of lead,nickel, and strontium nitrates on cell division and elongation in maize roots

The effects of Pb, Sr, and Ni nitrates on the root growth, its cell division and elongation were studied. Two-day-old maize seedlings were incubated on the 35 μM Ni(NO₃)₂, 10 μM Pb(NO₃)₂, or 3 mM Sr(NO₃)₂ in the presence or absence of 3 mM Ca(NO₃)₂. Metal toxicity was evaluated after the inhibition of root growth for the first and second days of incubation in comparison with the roots kept on water or Ca(NO₃)₂ solution. The contents of metals were determined in the apical (the first centimeter from the tip) and basal (the third centimeter from the kernel) root parts by voltamperometry and atomic-absorption spectrophotometry. We measured the length of the meristem, the length of the fully elongated cells, counted the mitotic index (MI) in the meristem and the number of meristematic cells in the cortex row; we also calculated duration the cell cycle. In the absence of Ca(NO₃)₂, the metal content in the apical root region was higher than in basal one. In the presence of Ca(NO₃)₂, we observed reverse ratio most pronounced in the case of Pb and Sr. All metals tested markedly reduced MI in the cortex, which was determined by the increase in the cell cycle duration and accompanied by the meristem shortening. These metals affected differently cell division and elongation: Ni inhibited mainly cell division and to a lesser degree their elongation, whereas Sr and Pb affected both cell division and elongation; only Sr treatment resulted in the increased length of the fully elongated cells. In the presence of Ca, all studied growth indices changed less than in the absence of Ca, which was manifested in the less severe suppression of the root growth and was in agreement with the lower accumulation of the metals in the root tips. Possible causes for the heavy metal action on growth are discussed in connection with the specificity of their transport and accumulation.     

Increased antioxidative capacity in maize calli during and after oxidative stress induced by a long lead treatment

Maize (Zea mays L., cv. Samodek) callus cultures were exposed for long period (22 months) to lead (0.5 mM lead chloride) and lead content, oxidative damage and antioxidative response were evaluated at different steps. Inductively coupled plasma (ICP) emission spectroscopy analysis showed that lead entered the cells and it accumulated, but its internal concentration was maintained 10-fold less than the external one. Increase of both polyamine and lipid peroxide content indicated that cells underwent a stress condition due to an oxidative attack, counteracted by an increase of antioxidative defence enzyme activities, ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2). After 10 months, from the start of the lead treatment, a stock of calli was transferred for 6 months in a lead-deprived medium and then re-exposed to lead for a further 6 months. Analysis indicated that lead-deprived calli maintained high levels of APX and GR activities, suggesting that, over the experimental time–course, cells with high APX and GR activity were selected and allowed to enrich the cultures. These cultures, after a new lead treatment, showed a lower oxidative damage compared to continuously lead-treated calli.     

Mutations in two independent genes lead to suppression of the shoot apical meristem in maize

The shoot apical meristem (SAM), initially formed during embryogenesis, gives rise to the aboveground portion of the maize (Zea mays) plant. The shootless phenotype (sml) described here is caused by disruption of SAM formation due to the synergistic interaction of mutations at two genetic loci. Seedlings must be homozygous for both sml (shootmeristemless), and the unlinked dgr (distorted growth) loci for a SAM-less phenotype to occur. Seedlings mutant only for sml are impaired in their morphogenesis to different extents, whereas the dgr mutation alone does not have a recognisable phenotype. Thus, dgr can be envisaged as being a dominant modifier of sml and the 12 (normal):3 (distorted growth):1 (shoot meristemless) segregation observed in the F(2) of the double heterozygote is the result of the interaction between the sml and dgr genes. Other segregation patterns were also observed in the F(2), suggesting instability of the dgr gene. Efforts to rescue mutant embryos by growth on media enriched with hormones have been unsuccessful so far. However, mutant roots grow normally on medium supplemented with kinetin at a concentration that suppresses wild-type root elongation, suggesting possible involvement of the mutant in the reception or transduction of the kinetin signal or transport of the hormone. The shootless mutant appears to be a valuable tool with which to investigate the organization of the shoot meristem in monocots as well as a means to assay the origins and relationships between organs such as the scutellum, the coleoptile, and leaves that are initiated during the embryogenic process.     

Plant architectural responses in simultaneous maize/soybean strip intercropping do not lead to a yield advantage

Maize/soybean strip intercropping is a commonly used system throughout China with high crop yields at reduced nutrient input compared to sole maize. Maize is the taller crop, and due to its dominance in light capture over soybean in the intercrop, maize is expected to outperform maize in sole cropping. Conversely, soybean is the subordinate crop and intercropped soybean plants are expected to perform worse than sole soybean. Crop plants show plastic responses in plant architecture to their growing conditions to forage for light and avoid shading. There is little knowledge on plant architectural responses to growing conditions in simultaneous (non-relay) intercropping and their relationship to species yields. A two-year field experiment with two simultaneous maize/soybean intercropping systems with narrow and wide strips was conducted to characterise architectural traits of maize and soybean plants grown as intercrop and sole crops. Intercropped maize plants, especially those in border rows, had substantially greater leaf area, biomass and yield than maize plants in sole crops. Intercropped soybean plants, especially those in border rows, had lower leaf area, biomass and yield than sole soybean plants. Overall intercrop performance was similar to that of sole crops, with the land equivalent ratio (LER) being only slightly greater than one (1.03–1.08). Soybean displayed typical shade avoidance responses in the intercrop, such as greater internode elongation and changes in specific leaf area, but these responses could not overcome the consequences of the competition with the taller maize plants. Therefore, in contrast to relay intercrop systems, in the studied simultaneous maize/soybean system, plastic responses did not contribute to practically relevant increases in resource capture and yield at whole system (i.e., intercrop) level.