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21.
Internal transport of O2 from the aerial tissues along the adventitious roots of intact maize plants was estimated by measuring the concentrations of adenine nucleotides in various zones along the root under an oxygen-free atmosphere. Young maize plants were grown in nutrient solution under conditions that either stimulated or prevented the formation of a lysigenous aerenchyma, and the roots (up to 210 mm long) were then exposed to an anaerobic (oxygen-free) nutrient solution. Aerenchymatous roots showed higher values than non-aerenchymatous ones for ATP content, adenylate energy charge and ATP/ADP ratios. We conclude that the lysigenous cortical gas spaces help maintain a high respiration rate in the tissues along the root, and in the apical zone, by improving internal transport of oxygen over distances of at least 210 mm. This contrasted sharply with the low energy status (poor O2 transport) in non-aerenchymatous roots.Abbreviation AEC
adenylate energy charge 相似文献
22.
Correlative light, high-voltage electron and conventional electron microscopic methods were used to investigate digestion in two allogromiid foraminiferans, Allogromia sp., strain NF, and A. laticollaris Arnold. Microscopic observations showed that bacterial prey are phagocytosed by reticulopodia and are transported to the allogromiid cell body within blister-like phagosomes. Larger prey (algae, diatoms) are transported along the reticulopodial surface and are either stored extrathalamously or phagocytosed at the oral opening (peduncle). Studies of allogromiids optimally fixed and labeled with an extracellular-space label (colloidal thorium) showed that phagocytosed prey are completely enclosed by a plasma membrane envelope; this finding was corroborated by a serial-section three-dimensional reconstruction of the oral zone of one allogromiid. Cytochemical staining for acid phosphatase showed that lysosomes are absent from reticulopods but abundant in the cell body, particularly in the oral zone cytoplasm. We conclude that digestion in allogromiid foraminiferans is accomplished by a vacuole-based digestive apparatus and not by extracellular digestion within a lacunary system, as has been suggested in earlier studies. 相似文献
23.
“Bulk density” and “dry-matter content” are useful indices of dry-matter accumulation in plant organs. A theoretical equation
describing the relationship between these two indices was put forward. To examine the reliability of this equation, the seasonal
changes of these two indices were investigated in the leaves and stems of different ages ofAucuba japonica. In each organ both indices varied seasonally almost parallel to each other, but the seasonal changes of dry-matter content
were less obvious than those of bulk density. The observed bulk density was always larger than that calculated from the observed
dry-matter content by the theoretical equation. A drying experiment showed that this discrepancy was caused by the decrement
of the volume of the plant material by water loss during the period from the weight measurement to the volume measurement.
When the water loss was negligible, the equation described well the relationships between the two indices of the experimental
materials. It was also shown that this equation was useful for the estimation of the amount of air space in plant materials. 相似文献
24.
Peter H. Barry 《The Journal of membrane biology》1984,82(3):221-239
Summary Many neurones are extremely invaginated and possess branching processes, axons and dendrites. In general, they are surrounded by a restricted diffusion space. Many of these cells exhibit large, slow potential changes during the passage of current across their membranes. Whenever currents cross membranes separating aqueous solutions, differences in transport numbers of the major permeant ions give rise to local concentration changes of these ions adjacent to the membranes, which will result in various electrical and osmotic effects. These transport number effects are expected to be enhanced by the presence of membrane invaginations. Dendrites are equivalent to reversed invaginations and there should be significant changes in concentrations of permeant ions within them. In general, the effects of such changes on the electrical response of a cell will be greater when the concentration of a major permeant ion is low. The effects have been modelled in terms of two nondimensional parameters: the invagination transport number parameter and the relative area occupied by the invaginations A. If these two parameters are known, the magnitudes and time course of the slow potential changes can immediately be estimated and the time course converted to real time, if the length of the invaginations (l) and ionic diffusion coefficient (D) within them are also known. Both analytical and numerical solutions have been given and predictions compared. It is shown that in the case of large currents and potentials the analytical solution predictions will underestimate the magnitudes and rates of onset of the voltage responses. The relative magnitude of the transport number effect within the invaginations (or dendrites) and other transport number contributions to slow potential changes have also been assessed and order-of-magnitude values of these are estimated for some biological data. 相似文献
25.
Production of bulblets of Muscari armeniacum through tissue culture is enhanced when 1 g/l activated charcoal is added to a modified Murashige and Skoog (MS) medium. Bulblet regeneration is direct from bulb scale explants with no intermediate callus growth. Bulblets can be transferred successfully to a greenhouse environment directly from aseptic culture. 相似文献
26.
Stanley W. Watson Eberhard Bock Frederica W. Valois John B. Waterbury Ursula Schlosser 《Archives of microbiology》1986,144(1):1-7
A new chemolithotrophic nitrite-oxidizing bacterium, for which the name Nitrospira marina is proposed, was isolated from the Gulf of Maine. N. marina is a Gramnegative curved rod which may form spirals with 1 to 12 turns. Cells have a unique periplasmic space and lack intracytoplasmic membranes and carboxysomes. N. marina is an obligate chemolithotroph, but best growth is obtained in a mixotrophic medium. N. marina may be one of the most prevalent nitrite-oxidizing bacteria in some oceanic environments. Type strain is field with American Type Culture Collection (ATCC 43039). 相似文献
27.
Z. Rengel 《Plant and Soil》1990,128(2):185-189
Ammonium acetate and BaCl2-triethanolamine were used to desorb Mg2+ from the root Donnan free space (DFS) of 23-d-old ryegrass (Lolium multiflorum Lam. cvs. Gulf and Wilo). Amounts of desorbed Mg2+ increased with the increase in Mg2+ activity of the nutrient solution. Slightly less Mg2+ was desorbed by Ba2+ than by NH4
+. Previously published data on short-term net Mg2+ uptake by intact 23-d-old ryegrass plants of the two cultivars were linearly related to the amount of exchangeable Mg+ desorbed from the root DFS (r2=0.90 and 0.81 for the desorption by NH4
+ and Ba2+, respectively). A sward of Mg2+ ions attracted to the negative charges of the cell surface is suggested to represent a part of a pool of Mg2+ available for active transport through the plasmalemma. 相似文献
28.
证候空间和方剂空间的数学结构 总被引:2,自引:0,他引:2
本文考察了中医理、法、方、药原理,给出了证候空间和方剂空间的数学结构,以利于中医现代化和中医临床中应用电子计算机诊疗技术。 相似文献
29.
Martijn A. Huynen 《Journal of molecular evolution》1996,43(3):165-169
RNA secondary-structure folding algorithms predict the existence of connected networks of RNA sequences with identical secondary
structures. Fitness landscapes that are based on the mapping between RNA sequence and RNA secondary structure hence have many
neutral paths. A neutral walk on these fitness landscapes gives access to a virtually unlimited number of secondary structures
that are a single point mutation from the neutral path. This shows that neutral evolution explores phenotype space and can
play a role in adaptation.
Received: 23 December 1995 / Accepted: 17 March 1996 相似文献
30.
On the mechanical characterization of compact bone structure using the homogenization theory 总被引:1,自引:0,他引:1
In a previous paper (Crolet et al., 1993, J. Biomechanics 26, 677–687), a modelling of the mechanical behavior of compact bone was presented, in which the homogenization theory was the basic tool of computation. In this simulation, approximations were used for the modelling of the lamellae and the osteons: the lamella and the osteon were divided into cylindrical sectors, each sector being approximated as a parallelepiped having a periodic structure (fibrous composite for the lamella, superimposition of plates for the osteon). The present study deals with a new model without these approximations. First, it can be proved that the homogenized elasticity tensor for a lamella, which has a non-periodic structure, is obtained at each geometrical point as a homogenized tensor of a periodic problem. Similarly, for the osteonal structure, the components of the homogenized tensor are determined at each point as the result of a periodic homogenization.
The software OSTEON, which is the computational method associated with this model, allows one to obtain a better understanding of the effects of many bony parameters. The obtained results are in accordance with experimental data. 相似文献