应用电子探针对植物根际和根内营养元素微区分布的探讨

用电子探针可检测出玉米、大豆根际和根内含有Na,Mg,Al,Si,P,S,Cl,K,Ca,Ti,Fe,Cu和Zn 13种元素。这些元素在根际土壤、粘液层和根组织内的含量分布有一定的规律性。除Si,Al,Ca,Fe在根际土壤中峰值较高外,Ti仅在土壤中达到可检测量;S,Fe和Zn富集在粘液层,Mg,P,Cl只在根组织内才有较明显的峰。这些规律可作为区分根—土界面的参考指标。K含量在根内明显高于根际土壤,并由表皮层到中柱径向增加;Ca则与K不同,且受植物种类的影响。     

Alteration in Neuronal-Glial Metabolism of Glutamate by the Neurotoxin Kainic Acid

The effect of the excitotoxin kainic acid on glutamate and glutamine metabolism was studied in cerebellar slices incubated with D-[2-14C]glucose, [U-14C]gamma-aminobutyric acid, [3H]acetate, [U-14C]glutamate, and [U-14C]glutamine as precursors. Kainic acid (1 mM) strongly inhibited the labeling of glutamine relative to that of glutamate from all precursors except [2-14C]glucose and [U-14C]glutamine. Kainic acid did not inhibit glutamine synthetase directly. The data indicate that in the cerebellum kainic acid inhibits the synthesis of glutamine from the small pool of glutamate that is thought to be associated with glial cells. Kainic acid also markedly stimulated the efflux of glutamate from cerebellar slices and this release was not sensitive to tetrodotoxin. Kainic acid stimulated efflux of both glucose- and acetate-labeled glutamate. In contrast, veratridine released glucose-labeled glutamate preferentially via a tetrodotoxin-sensitive mechanism. Kainic acid did not release [U-14C]glutamate from synaptosomal fractions. These results suggest that the bulk of the glutamate released from cerebellar slices by kainic acid comes from nonsynaptic pools.     

HLAMP – a conjugate of hippuryllysine and AMP which contains a phosphoamide bond – stimulates chemotaxis in Dictyostelium discoideum

A conjugate of hippuryllysine (HP) and adenylic acid was synthesized and purified. The structure of the conjugate, hippuryllysyl(N-epsilon-5'-phospho)adenosine (HLAMP) was established using 31P nuclear magnetic resonance, UV spectroscopy, acid/base lability, and enzyme digestion with AMP deaminase, alkaline phosphatase, 5'-nucleotidase, and a phosphoamidase activity recently identified in Dictyostelium discoideum. The results indicate that HLAMP contains a phosphoamide bond between the phosphate of AMP and the epsilon amino group of HL. Employing a microdroplet assay to assess chemotactic activity, HLAMP was found to be a potent chemoattractant of 7-h developing amoebae of D. discoideum. Other conjugates, including lysine-AMP (LAMP), tuftsin-AMP (TAMP) and avidin-AMP (AVAMP), as well as the degradation products of HLAMP (HL, AMP, and lysine) exhibited no chemotactic activity. The molecular structure of HLAMP is compared to that of other known chemoattractants of the cellular slime molds, and possible chemotactic receptors for HLAMP are considered.     

Characterization of the protein import apparatus in isolated outer envelopes of chloroplasts

Isolated outer envelope membrane from pea (Pisum sativum L.) chloroplasts can be used in vitro to study binding and partial translocation of precursor proteins destined for the inside of the organelle. Efficient binding to a receptor protein on the outside of the membrane vesicle and generation of a translocation intermediate depends strictly on the presence of ATP. Protease treatment of the translocation intermediate demonstrates its insertion into the membrane. The membrane-inserted precursor protein cannot be extracted by 1 M NaCl and is also NaOH resistant to a large extent. Mild solubilization of outer envelope membranes by detergent resulted in the isolation of a complex which still contained the precursor protein. We have identified a constitutively expressed homologue hsc 70 as part of this membrane complex. Antibodies against hsp 70 (inducible heat shock protein 70) were able to immuno-precipitate the complex bound precursor protein. A second protein of 86 kDa molecular weight (OEP 86) from the outer envelope membrane was also identified as a major component of this complex.     

Impacts of population growth and economic development on the nitrogen cycle in Asia

Asia is the major consumer of fertilizer nitrogen and energy in the world, and consequently shares a considerable proportion of the world creation of reactive nitrogen (Nr). However, if estimated on per capita basis, Asia is characterized by a lower arable land area, fertilizer nitrogen consumption, energy consumption, and gross domestic product, as well as lower daily protein intake. To meet the increasing needs for food and energy for the growing population combined with the improvement of living standards, Nr will inevitably increase. The present study estimates the creation of Nr and the emissions of various N compounds into environment in Asia currently and in 2030. In comparison with the world averages, the lower fertilizer nitrogen and energy use efficiencies, and the lower use of animal wastes for agriculture imply that there is potential for moderating the increase in Nr and its impacts on the environment. Strategies for moderating the increase are discussed.     

Capitalizing on multi-element interactions through bal-anced nutrition——A pathway to improve nitrogen use efficiency in China,India and North America

A viable option for increasing nitrogen (N) use efficiency and mitigation of negative impacts of N on the environment is to capitalize on multi-element interactions through implementation of nutrient management programs that provide balanced nutrition. Numerous studies have demonstrated the immediate efficacy of this approach in the developing regions like China and India as well as developed countries in North America. Based on 241 site-years of experiments in these countries, the first-year N recovery efficiency (RE) for the conventional or check treatments averaged 21% while the balanced treatments averaged 54% RE, for an average increase of 33% in RE due to balanced nutrition. Effective policies to promote adoption are most likely those that enable site-specific approaches to nutrient management decisions rather than sweeping, nation-wide incentives supporting one nutrient over another. Local farmers, advisers and officials need to be empowered with tools and information to help them define necessary changes in practices to create more balanced nutrient management.     

Pretreatment with H_2O_2 Alleviates Aluminum-induced Oxidative Stress in Wheat Seedlings

Hydrogen peroxide(H2O2) is a key reactive oxygen species(ROS) in signal transduction pathways leading to activation of plant defenses against biotic and abiotic stresses.In this study,we investigated the effects of H2O2 pretreatment on aluminum(Al) induced antioxidant responses in root tips of two wheat(Triticum aestivum L.) genotypes,Yangmai-5(Al-sensitive) and Jian-864(Al-tolerant).Al increased accumulation of H2O2 and O2r· leading to more predominant lipid peroxidation,programmed cell death and root elon...     

垦殖对新疆绿洲农田土壤有机碳组分及团聚体稳定性的影响

土壤有机碳是土壤质量变化的重要指标,土壤活性有机碳组分在土壤质量变化方面发挥重要作用。采用有机碳分组技术,研究了干旱荒漠区自然土壤开垦对绿洲农田土壤有机碳活性组分及团聚体稳定性的影响。结果表明:低有机碳含量的自然土壤垦殖后,有利于干旱荒漠区绿洲棉田土壤有机碳的积累,且垦殖(0-5a)增加显著,年均增加在0.65gkg-1以上,上升幅度为76%-286%,5a后维持在相对平衡的水平;土壤活性有机碳、轻组有机碳在垦殖0-5a显著增加,平均增加72%和99%,5a后下降;颗粒有机碳则表现出垦殖0-10a明显增加,增加在275%以上,10a后下降;土壤水稳性团聚体含量随垦殖年限的延长显著增加,0-20a内较自然土壤提高了75%。垦殖可能是干旱区绿洲农田潜在碳汇的重要影响因素;但随垦殖年限延长,土壤有机碳活性组分下降,土壤质量又存在一定的退化风险。     

黑腐皮壳属一新种

本文报道发生于我国沈阳地区落叶松枝上的一个新种——大孢黑腐皮壳(Valsa macro-spora sp.nov.)。新种的子囊孢子在15μm以上,属于大型种。其形态特征有汉文和拉丁文描述及其培养性状的记述。     

杨梅根结线虫病及其病原鉴定

本文报道对杨梅根结线虫病的研究及病原鉴定结果。该病症状为:病树根部形成大小不一的根结,内有乳白色囊状雌虫及棕色卵囊;后期根结腐烂,病树叶片黄化脱落,梢枯乃至死亡。病原鉴定确认,引起该病的根结线虫有3个种:爪哇根结线虫(Meloidogyne javanica)、南方根结线虫(M.incognita)和北方根结线虫(M. hapla)。爪哇根结线虫为优势种。