肥料三要素对六龄参根产量影响的数量分析

本文针对长白山区低肥力白浆土壤,在三因素五水平最优回归设计田间试验的基础上,应用多元统计分析的方法,建立了氮磷钾三种肥料对六龄参根产量影响的肥料效应数学模型。通过对此模型的数学分析,得知氮磷钾三种肥料对六龄参根的产量均有显著影响。其综合增产效应依次为NK＞N＞K＞P,而三种肥料的线性增产效应依次为N＞K＞P。当三种肥料在一定条件下单独使用时,其增产效应依次为N＞K＞P。同时确定了最高产量施肥量和最大利润施肥量,由等产线确定了合理施肥区。     

Germination and seedling establishment of two annual grasses on lichen-dominated biological soil crusts

Biological soil crusts dominated by lichens are common components of shrub-steppe ecosystems in northwestern US. We conducted growth chamber experiments to investigate the effects of these crusts on seed germination and initial seedling establishment of two annual grasses; the highly invasive exotic Bromus tectorum L. and the native Vulpia microstachys Nutt. We recorded germination time courses on bare soil and two types of biological soil crusts; one composed predominantly of the lichen Diploschistes muscorum (Scop.) R. Sant. (lichen crust) and the other comprised of an assortment of lichens and mosses (mixed crust). Final germination on the lichen crust for both grass species was about a third of that on the bare soil surface. Mean germination time (MGT) was 3–4 days longer on the lichen crust compared with the bare soil. In contrast, there was no difference in germination percentage or MGT between the mixed crust and bare soil, and results were similar for both grass species. For both species, root penetration of germinating seeds on the lichen crust was lower than on the bare soil or mixed crust surfaces. The combined effects of the lichen crust on germination and root penetration resulted in an overall reduction in seedling establishment of 78% for V. microstachys and 85% for B. tectorum relative to the bare soil treatment. Our results clearly demonstrate that lichen-dominated biological soil crust can inhibit germination and root penetration, but the extent of these effects depends on the composition of the crust. Responsible Editor: Tibor Kalapos     

电阻抗法在植物根系生物学研究中的应用

因受限于检测方法,对埋藏于土壤中植物根系研究的深入程度远低于其地上部分。传统获取根系的方法不仅费时费力,而且对根系原位分布和生存微环境具有明显的扰动破坏,故随着根系研究的不断深入,迫切需要寻求一种非破坏性的根系检测方法。电阻抗法是在一定频率的外加电源下,测量电路中的根系电学特征(电容、电阻和电阻抗图谱),并且电学特征与根系生物量和形态指标之间存在较好的相关性,然而,由于对电阻抗法基于电路中电流流向等的关键机理尚不清楚,有些学者对该方法的大范围应用提出了质疑。本文首先对生物电阻抗法测量根系的原理和模型进行阐述,然后重点综述根系电阻抗法研究的不同理论方法及存在的问题,最后提出电阻抗法研究植物根系应该解决的重要科学问题,并展望电阻抗法更加广泛的研究和应用前景,以期为获取非破坏性的根系研究技术提供参考。     

Dihydroactinidiolide,a natural product against Aβ25-35 induced toxicity in Neuro2a cells: Synthesis,in silico and in vitro studies

Synthesis of natural products has speeded up drug discovery process by minimizing the time for their purification from natural source. Several diseases like Alzheimer's disease (AD) demand exploring multi targeted drug candidates, and for the first time we report the multi AD target inhibitory potential of synthesized dihydroactinidiolide (DA). Though the activity of DA in several solvent extracts have been proved to possess free radical scavenging, anti bacterial and anti cancer activities, its neuroprotective efficacy has not been evidenced yet. Hence DA was successfully synthesized from β-ionone using facile two-step oxidation method. It showed potent acetylcholinesterase (AChE) inhibition with half maximal inhibitory concentration (IC₅₀) 34.03 nM, which was further supported by molecular docking results showing strong H bonding with some of the active site residues such as GLY117, GLY119 and SER200 of AChE. Further it displayed DPPH and (.NO) scavenging activity with IC₅₀ value 50 nM and metal chelating activity with IC₅₀ >270 nM. Besides, it significantly prevented amyloid β_25-35 self-aggregation and promoted its disaggregation at 270 nM. It did not show cytotoxic effect towards Neuro2a (N2a) cells up to 24 h at 50 and 270 nM while it significantly increased viability of amyloid β_25-35 treated N2a cells through ROS generation at both the concentrations. Cytotoxicity profile of DA against human PBMC was quite impressive. Hemolysis studies also revealed very low hemolysis i.e. minimum 2.35 to maximum 5.61%. It also had suitable ADME properties which proved its druglikeness. The current findings demand for further in vitro and in vivo studies to develop DA as a multi target lead against AD.     

Identification of nifE-, nifN- and nifS-like genes in Bradyrhizobium japonicum

Summary The 17 kb region between the Bradyrhizobium japonicum nitrogenase genes (nifDK and nifH) was investigated for the presence of further nif or fix genes by site-directed insertion or deletion/replacement mutagenesis and interspecies hybridization. Mutant strains were tested for their ability to reduce acetylene in free-living, microaerobic culture (Nif phenotype) and in soybean root nodules (Fix phenotype). The presence of a gene, previously identified by hybridization with the Klebsiella pneumoniae nifB gene, was proved by isolation of a nifB insertion mutant which was completely Nif^- and Fix^-. Three other regions were found to be homologous to the K. pneumoniae genes nifE, nifN, and nifS, NifE and nifN insertion mutants were completely Nif^-/Fix^- whereas nifS mutants were leaky with 30% residual Fix activity. Taken together, the data show that the B. japonicum genome harbours a cluster of closely adjacent genes which are directly concerned with nitrogenase function.     

Response of cassava to water stress

Summary Cassava (Manihot esculenta Crantz) is a staple food for a large sector of human population in the tropics. It is widely produced for its starchy roots by small farmers over a range of environments on poor infertile soils with virtually no inputs. It is highly productive under favorable conditions and produces reasonably well under adverse conditions where other crops fail. The crop, once established, cansurvive for several months without rain. There is a wide variation within the cassava germplasm for tolerance to prolonged drought and the possibility to breed and select for stable and relative high yields under favorable and adverse conditions does indeed exist. Research with several cassava clones at CIAT has shown that high root yield under mid—term stress is not incompatible with high yield under nonstress conditions. Plant types with high yield potential under both conditions (e.g. the hybrid CM 507-37) are characterized by having slightly higher than optimum leaf area index under nonstress conditions, higher leaf area ratio and more intensive and extensive fine root system.     

Transfer to wheat of the copper efficiency factor carried on rye chromosome arm 5RL

Summary Rye carries a gene(s) on the long arm of chromosome 5 which confers the ability to tolerate soils too copper-deficient for wheat. Because many South Australian soils are low in copper, copper deficiency in wheat is common. To overcome this problem, wheats were bred having the rye chromosome arm (5RL) attached to a wheat chromosome. The presence of the rye 5RL chromosome segment in four different wheat cultivars increased grain yield on copper-deficient soils by more than 100% on average. Effects in vegetative yields were also significant at stem extension. Copper concentrations were on average little higher in plant tissues of 5R lines than in the controls but copper uptake was greater, in proportion to yield. Possible mechanisms of the copper efficiency factor are discussed.     

The allelopathic potential of alfalfa root medicagenic acid glycosides and their fate in soil environments

Summary The allelopathic effect of alfalfa (Medicago media Pers.) and red clover (Trifolium pratense L.) root saponins on winter wheat seedling growth and the fate of these chemicals in soil environments were studied. Seed germination, seedling and test fungus growth were suppressed by water and by alcohol extracts of alfalfa roots, and by crude saponins of alfalfa roots, indicating that medicagenic acid glycosides are the inhibitor. Powdered alfalfa roots inhibited wheat seedling growth when added to sand. At concentrations as low as 0.25% (w/w) the root system was completely destroyed whereas seedling shoots suffered little damage. Red clover roots caused some wheat growth inhibition when incorporated to sand, but their effect was much lower than in the alfalfa root treatment. Soil textures had a significant influence on the inhibitory effect of alfalfa roots. The inhibition of seedling growth was more pronounced on light than on heavy soils. This was attribted to the higher sorption of inhibitors by heavy soils. Incubation of alfalfa roots mixed into loose sand, coarse sand, loamy sand and clay loam for a period of 0–8 days resulted in decreased toxicity to bothT. viride and wheat seedlings. This decrease occurred more quickly in heavier soils than in loose sand, due to the hydrolysis of glycosides by soil microorganisms. Soil microbes were capable of detoxifying medicagenic acid glycosides by partial hydrolysis of sugar chain to aglycone. These findings illustrate the importance of medicagenic acid glycosides as an inhibitor of wheat seedling growth, and of their fate in different soil environments.     

Total and CO-reactive heme content of actinorhizal nodules and the roots of some non-nodulated plants

Summary The concentration of total and CO-reactive heme was measured in actinorhizal nodules from six different genera. This gave the upper limit to hemoglobin concentration in these nodules. Quantitative extraction of CO-reactive heme was achieved under anaerobic conditions in a buffer equilibrated with CO and containing Triton X-100. The concentration of CO-reactive heme in nodules of Casuarina and Myrica was approximately half of that found in legume nodules, whereas in Comptonia, Alnus and Ceanothus the concentrations of heme were about 10 times lower than in legume nodules. There was no detectable CO-reactive heme in Datisca nodules, but low concentrations were detected in roots of all non-nodulating plants examined, includingZea mays. Difference spectra of CO treated minus dithionite-reduced extracts displayed similar wavelengths of maximal and minimal light absorption for all extracts, and were consistent with those of a hemoglobin. The concentration of CO-reactive heme was not correlated to the degree to which CO inhibited nitrogenase activity nor was it affected by reducing the oxygen concentration in the rooting zone. However, there was a positive correlation between heme concentration and suberization or lignification of the walls of infected host cells. These observations demonstrate that, unlike legume nodules, high concentrations of heme or hemoglobin are not needed for active nitrogen fixation in most actinorhizal nodules. Nonetheless, a significant amount of CO-reactive heme is found in the nodules of Alnus, Comptonia, and Ceanothus, and in the roots ofZea mays. The identity and function of this heme is unknown.     

The effect of abscisic acid on cell turgor pressures,solute content and growth of wheat roots

Abscisic acid (ABA) was shown to influence turgor pressure and growth in wheat (Triticum aestivum L.) roots. At a concentrations of 25 mmol·m^-3, ABA increased the turgor pressure of cells located within 1 cm of the tip by up to 450 kPa. At 4 to 5 cm from the root tip this concentration of ABA reduced the turgor pressure of peripheral cells (epidermis and the first few cortical cell layers) to zero or close to zero while that of the inner cells was increased. Increases in sap osmolality were dependent on the concentration of ABA and the effect saturated at 5 mmol·m^-3 ABA. The increase in osmolality took about 4 h and was partly the result of reducing-sugar accumulation. Levels of inorganic cations were not affected by ABA. Root growth was inhibited at ABA concentrations that caused a turgor-pressure increase. The results show that while ABA can affect root cell turgor pressures, this effect does not result in increased root growth.Abbreviation ABA abscisic acid