Isolation and analysis of gas bubbles in the cavities of Azolla leaves

A procedure has been developed for the isolation of gas bubbles from the cavities of leaves of Azolla rubra. Mature leaves of exponentially growing Azolla plants were carefully cut under water with a razor blade. The gas bubbles in the cavities were driven out by a stream of water running from a glass capillary and collected in another capillary that was filled with distilled water. This allowed the collection of a sufficient number of gas bubbles for analysis. The concentration of oxygen in the gas obtained was slightly lower than that in the external air. The diffusion of external ¹⁵N₂ into the gas bubbles was low. The concentration of ¹⁵N₂ in gas bubbles was only 2% of that of the external air even after incubation of Azolla plants in ¹⁵N₂ in light or in darkness for 20 h. The method described here for isolation and analysis of gas bubbles should permit further studies of the properties of the gas bubbles in the cavities of Azolla leaves.     

A reaction diffusion model of C-N-S-O species in a stratified sediment

Abstract The model represents a System Dynamics approach to the solution of a reaction-diffusion problem involving biogeochemical processes in a stratified marine sediment. The major reactants and products are represented, their interactions described by Michelis Menton-like equations and their movements controlled by diffusion equations. The model is truly dynamic: all reaction-and diffusion rates of all specified species are predicted by the model in space and time. In order to simplify the output, a steady-state situation is examined where the variation in oxygen, nitrate and ammonium concentrations, and the rates of nitrification and denitrification are seen in relation to different levels of organic matter mineralization. Nitrogen and carbon budgets are also presented. The modelling environment, Cellmatic, was designed to run models with high spatial and temporal structure. Cellmatic is easy to use for simulating any model with these characteristics.     

Detopping causes production of intercellular space occlusions in both the cortex and infected region of soybean nodules

A structural analysis was conducted to determine whether glycoprotein‐containing intercellular space occlusions are involved in medium‐term regulation of O₂ diffusion in soybean (Glycine max) nodules. Alterations in O₂ diffusion were induced by a 3 h detopping treatment, and glycoprotein was immunolocalized with the monoclonal antibodies MAC236 and MAC265. Western blots of unstressed nodules revealed that these antibodies recognize antigens with two different molecular weights in soybean nodules. Tissue printing of halved nodules showed that both antigens were present in fresh nodules from control and 3 h detopped plants. The main localization appeared to be the inner cortex, but some immunolabelling also occurred in the infected region. ELISAs demonstrated a significant increase in total nodule concentration of intercellular glycoprotein following detopping, and cryosections of fresh nodules from this treatment also showed localization of antigens within the intercellular spaces of the infected region. The production of intercellular space occlusions in both the mid‐cortex and infected regions after 3 h detopping was confirmed by light microscopy and silver‐enhanced immunolabelling; cortical changes were quantified by image analysis techniques. Electron microscopy revealed that the occlusions within the infected region were less dense and less heavily labelled than those in the cortex. These results are discussed in relation to O₂ diffusion regulation in soybean nodules     

胶蚧属昆虫的自然分布扩散及地理起源(半翅目:胶蚧科)

在对南亚、东南亚及邻近地区胶蚧属昆虫分布资料归纳的基础上,结合近年实地调查资料,提出了胶蚧属昆虫的自然分布、扩散路线及地理起源。结果如下:胶蚧属昆虫主要分布在南亚、东南亚及邻近地区,主要包括中国、印度、巴基斯坦、孟加拉国、尼泊尔、不丹、缅甸、泰国、老挝、越南、马来西亚、印度尼西亚、菲律宾、澳大利亚等地。胶蚧属昆虫有2个分布区,即南亚分布区和东南亚分布区。国际流域恒河、印度河、布拉马普特拉河、萨尔温江-怒江、澜沧江-湄公河、元江-红河及它们的部分支流是胶蚧属昆虫扩散的通道。南亚扩散路线以印度为中心,分别向北、向西和向东3个方向扩散;东南亚扩散路线以马来西亚为中心,向北扩散。胶蚧属昆虫有2个地理起源,南亚范围以印度为中心,东南亚范围内以马来西亚为中心。胶蚧属昆虫的寄主植物是其分布扩散的先决条件,气候条件是限制分布扩散的关键因子。     

Ventilation and respiration in roots of one-year-old seedlings of grey mangrove Avicennia marina (Forsk.) Vierh.

Avicennia marina (Forsk.) Vierh. was grown from seed for 12 months in artificially tidal tanks providing a range of duration and depth of inundation. Plant growth characteristics were measured at harvest. Root aerenchyma development was estimated by pycnometry, root respiration rates by manometry, and the oxygen supply capacity of the above-ground portions of the plant was determined using oxygen electrode chambers. The mass per plant at harvest was influenced by the extent of inundation during growth with maximal growth at intermediate-length (1.5 to 6.5 h per tide) inundation periods. Those plants that had been submerged the longest (8.5 h per tide) had the least root tissue. The oxygen conductance of the stem base plus any pneumatophores showed a maximum in plants grown under intermediate inundation. Oxygen demand and internal gas space per unit dry weight of root were independent of extent of inundation. During high tide the plants grown at inundation periods of more than about 3–5 hours per tide were likely to become anaerobic. This may constitute a physiological limit for this species at the bottom of the tidal range.     

Effects of genetic drift on variance components under a general model of epistasis

We analyze the changes in the mean and variance components of a quantitative trait caused by changes in allele frequencies, concentrating on the effects of genetic drift. We use a general representation of epistasis and dominance that allows an arbitrary relation between genotype and phenotype for any number of diallelic loci. We assume initial and final Hardy-Weinberg and linkage equilibrium in our analyses of drift-induced changes. Random drift generates transient linkage disequilibria that cause correlations between allele frequency fluctuations at different loci. However, we show that these have negligible effects, at least for interactions among small numbers of loci. Our analyses are based on diffusion approximations that summarize the effects of drift in terms of F, the inbreeding coefficient, interpreted as the expected proportional decrease in heterozygosity at each locus. For haploids, the variance of the trait mean after a population bottleneck is var(delta(z)) = sigma(n)k=1 FkV(A(k)), where n is the number of loci contributing to the trait variance, V(A(1)) = V(A) is the additive genetic variance, and V(A(k)) is the kth-order additive epistatic variance. The expected additive genetic variance after the bottleneck, denoted (V*(A)), is closely related to var(delta(z)); (V*(A)) = (1 - F) sigma(n)k=1 kFk-1V(A(k)). Thus, epistasis inflates the expected additive variance above V(A)(1 - F), the expectation under additivity. For haploids (and diploids without dominance), the expected value of every variance component is inflated by the existence of higher order interactions (e.g., third-order epistasis inflates (V*(AA. This is not true in general with diploidy, because dominance alone can reduce (V*(A)) below V(A)(1 - F) (e.g., when dominant alleles are rare). Without dominance, diploidy produces simple expressions: var(delta(z)) = sigma(n)k=1 (2F)kV(A(k)) and (V(A)) = (1 - F) sigma(n)k=1 k(2F)k-1V(A(k)). With dominance (and even without epistasis), var(delta(z)) and (V*(A)) no longer depend solely on the variance components in the base population. For small F, the expected additive variance simplifies to (V*(A)) approximately equal to (1 - F)V(A) + 4FV(AA) + 2FV(D) + 2FC(AD), where C(AD) is a sum of two terms describing covariances between additive effects and dominance and additive X dominance interactions. Whether population bottlenecks lead to expected increases in additive variance depends primarily on the ratio of nonadditive to additive genetic variance in the base population, but dominance precludes simple predictions based solely on variance components. We illustrate these results using a model in which genotypic values are drawn at random, allowing extreme and erratic epistatic interactions. Although our analyses clarify the conditions under which drift is expected to increase V(A), we question the evolutionary importance of such increases.     

Long-distance transport of gases in plants: a perspective on internal aeration and radial oxygen loss from roots

Internal transport of gases is crucial for vascular plants inhabiting aquatic, wetland or flood‐prone environments. Diffusivity of gases in water is approximately 10 000 times slower than in air; thus direct exchange of gases between submerged tissues and the environment is strongly impeded. Aerenchyma provides a low‐resistance internal pathway for gas transport between shoot and root extremities. By this pathway, O₂ is supplied to the roots and rhizosphere, while CO₂, ethylene, and methane move from the soil to the shoots and atmosphere. Diffusion is the mechanism by which gases move within roots of all plant species, but significant pressurized through‐flow occurs in stems and rhizomes of several emergent and floating‐leaved wetland plants. Through‐flows can raise O₂ concentrations in the rhizomes close to ambient levels. In general, rates of flow are determined by plant characteristics such as capacity to generate positive pressures in shoot tissues, and resistance to flow in the aerenchyma, as well as environmental conditions affecting leaf‐to‐air gradients in humidity and temperature. O₂ diffusion in roots is influenced by anatomical, morphological and physiological characteristics, and environmental conditions. Roots of many (but not all) wetland species contain large volumes of aerenchyma (e.g. root porosity can reach 55%), while a barrier impermeable to radial O₂ loss (ROL) often occurs in basal zones. These traits act synergistically to enhance the amount of O₂ diffusing to the root apex and enable the development of an aerobic rhizosphere around the root tip, which enhances root penetration into anaerobic substrates. The barrier to ROL in roots of some species is induced by growth in stagnant conditions, whereas it is constitutive in others. An inducible change in the resistance to O₂ across the hypodermis/exodermis is hypothesized to be of adaptive significance to plants inhabiting transiently waterlogged soils. Knowledge on the anatomical basis of the barrier to ROL in various species is scant. Nevertheless, it has been suggested that the barrier may also impede influx of: (i) soil‐derived gases, such as CO₂, methane, and ethylene; (ii) potentially toxic substances (e.g. reduced metal ions) often present in waterlogged soils; and (iii) nutrients and water. Lateral roots, that remain permeable to O₂, may be the main surface for exchange of substances between the roots and rhizosphere in wetland species. Further work is required to determine whether diversity in structure and function in roots of wetland species can be related to various niche habitats.     

改进的免疫双向扩散方法及其应用

介绍了一种改进的免疫双向扩散方法及其在重组呼吸道合胞病毒(RSV)疫苗研制中的用途。本法在琼脂凝胶中附加0．1μg／mL左右的澳酚蓝,使凝胶呈淡蓝色,与抗原一抗体复合物产生的白色沉淀线形成较大的反差,可显示出比较微弱的沉淀线,因而改善了免疫双向扩散法的灵敏度。用这种改进的方法检测RSV抗血清滴度、筛查RSV阳性小鼠以及检测重组RSV蛋白疫苗的抗原反应性,均取得了较传统方法更佳的效果。     

Effect of preferential solvation and bimolecular quenching reactions on 3OCE in acetonitrile and 1,4‐dioxane binary mixtures by optical absorption and fluorescence studies

Fluorescence quenching and preferential solvation of a coumarin derivative, namely 3‐[2‐oxo‐2‐(2‐oxo‐2H‐chromen‐3‐yl)‐ethylidene]‐1,3‐dihydro‐indol‐2‐one (3OCE), with aniline used as a quencher in solvent mixtures of acetonitrile (AN) and 1,4‐dioxane (DX) was carried out at steady state. Suppan's theory of dielectric enrichment was used to understand the nonideality and dielectric enrichment in AN–DX solvent mixtures. The effect of viscosity and dielectric constant variation at room temperature were analyzed. Quenching was characterized using Stern–Volmer plots with an upward curvature. It was found that 3OCE underwent combined static and dynamic quenching that was evident from the quenching rate parameters.