铁皮石斛的离体开花

铁皮石斛(Dendrobium candidum),为一种野生兰科植物,在栽培条件下,从种子萌发到开花通常需要3～4a.研究了多种植物激素和多胺对该种石斛组织培养中花芽形成的影响,结果表明在培养基中加入合适浓度的亚精胺(spermidine)或BA(6-苄基腺嘌呤),或同时加入NAA(萘乙酸)和BA均可诱导原球茎或由之形成的无根小苗在3～6个月开花,频率在31.6%～45.8%.当将原球茎在加有ABA(脱落酸)的培养基上预培养后再移到加有BA的培养基上,花芽形成的频率可提高到平均达82.8%(个别实验中可达100%),这种诱导提早开花的现象也与实验材料的发育阶段(原球茎、无根小苗、已生根的小苗)有关,通常发生在根的形成受到完全或部分抑制的情况中.     

ConA激活小鼠胸腺T淋巴细胞增殖过程中c-myc与核骨架蛋白的结合

采用DNA-蛋白质体外吸附的方法研究伴刀豆球蛋白激活小鼠胸腺T淋巴细胞增殖过程中c-myc与核骨架蛋白的结合.实验结果显示,c-myc与核骨架蛋白的结合具有特异性,在淋巴细胞激活过程中c-myc与P₃₄/P₃₆核骨架蛋白及核纤层蛋白结合,并发生动态变化.     

Efficiencies of different genes and different tree-building methods in recovering a known vertebrate phylogeny

The relative efficiencies of different protein-coding genes of the mitochondrial genome and different tree-building methods in recovering a known vertebrate phylogeny (two whale species, cow, rat, mouse, opossum, chicken, frog, and three bony fish species) was evaluated. The tree-building methods examined were the neighbor joining (NJ), minimum evolution (ME), maximum parsimony (MP), and maximum likelihood (ML), and both nucleotide sequences and deduced amino acid sequences were analyzed. Generally speaking, amino acid sequences were better than nucleotide sequences in obtaining the true tree (topology) or trees close to the true tree. However, when only first and second codon positions data were used, nucleotide sequences produced reasonably good trees. Among the 13 genes examined, Nd5 produced the true tree in all tree-building methods or algorithms for both amino acid and nucleotide sequence data. Genes Cytb and Nd4 also produced the correct tree in most tree-building algorithms when amino acid sequence data were used. By contrast, Co2, Nd1, and Nd41 showed a poor performance. In general, large genes produced better results, and when the entire set of genes was used, all tree-building methods generated the true tree. In each tree-building method, several distance measures or algorithms were used, but all these distance measures or algorithms produced essentially the same results. The ME method, in which many different topologies are examined, was no better than the NJ method, which generates a single final tree. Similarly, an ML method, in which many topologies are examined, was no better than the ML star decomposition algorithm that generates a single final tree. In ML the best substitution model chosen by using the Akaike information criterion produced no better results than simpler substitution models. These results question the utility of the currently used optimization principles in phylogenetic construction. Relatively simple methods such as the NJ and ML star decomposition algorithms seem to produce as good results as those obtained by more sophisticated methods. The efficiencies of the NJ, ME, MP, and ML methods in obtaining the correct tree were nearly the same when amino acid sequence data were used. The most important factor in constructing reliable phylogenetic trees seems to be the number of amino acids or nucleotides used.      

Phosphorylation of smooth muscle myosin by type II Ca2+/calmodulin-dependent protein kinase

Brain type II Ca²⁺/calmodulin-dependent protein kinase was found to phoshorylate smooth muscle myosin, incorporating maximally 2 mol of phosphoryl per mol of myosin, exclusively on the 20,000 dalton light chain subunit. After maximal phosphorylation of myosin or the isolated 20,000 dalton light chain subunit by myosin light chain kinase, the addition of type II Ca²⁺/calmodulin-dependent protein kinase led to no further incorporation indicating the two kinases phosphorylated a common site. This conclusion was supported by two dimensional mapping of tryptic digests of myosin phosphorylated by the two kinases. By phosphoamino acid analysis the phosphorylated residue was identified as a serine. The phosphorylation by type II Ca ²⁺/calmodulin-dependent protein kinase of myosin resulted in enhancement of its actin-activated Mg²⁺-ATPase activity. Taken together, these data strongly support the conclusion that type II Ca²⁺/calmodulin-dependent protein kinase phosphorylates the same amino acid residue on the 20,000 dalton light chain subunit of smooth muscle myosin as is phosphorylated by myosin light chain kinase and suggest an alternative mechanism for the regulation of actin-myosin interaction.Abbreviations SDS-PAGE Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis - EGTA Ethylene Glycol Bis (-amino-ethyl ether)-N,N,N,N-Tetraacetic Acid - DTT Dithiothreitol - LC₂₀ Gizzard Smooth Muscle Phosphorylatable 20 kDa Myosin Light Chain - LC₁₇ Gizzard Smooth Muscle, 17 kDa Myosin Light Chain - H Chain Gizzard Smooth Muscle 200 kDa Myosin Heavy Chain - TPCK L-1-Tosylamido-2-Phenylethyl Chloromethyl Ketone - MOPS 3-(N-morpholino) Propanesulfonic Acid     

CONDUCTIVITY AND PERMEABILITY

An electrical current passing through a living plant flows partly through the cell wall and partly through the protoplasm. The relative amounts of these two portions of the current can be calculated. The outcome of such calculations shows that the conclusions drawn from the study of the resistance of the tissue as a whole apply also to the resistance of the protoplasm, and consequently to the permeability of the protoplasm to ions.     

PROTOPLASMIC ASYMMETRY IN NITELLA AS SHOWN BY BIOELECTRIC MEASUREMENTS

Using multinucleate cells of Nitella 2 or 3 inches in length it is possible to kill one end with chloroform without producing at the other any immediate alteration which can be detected by our present methods. When a spot in external contact with sap is killed its potential difference falls approximately to zero and it is therefore possible to measure the potential difference across the protoplasm at any desired point merely by leading off from that point to the one where the protoplasm has been killed. The results indicate that the inner and outer protoplasmic surfaces differ, for when both surfaces are in contact with the same solution (cell sap) there is an electromotive force of about 15.9 millivolts, the inner surface being positive to the outer (i.e. the positive current tends to flow from the inner surface through the electrometer to the outer surface). The situation resembles that in Valonia where the corresponding value (with Valonia sap applied to the outside) has been reported as about 14.5 millivolt (the inner surface being positive to the outer). It would seem appropriate to designate this as radial polarity.     

THE DEATH WAVE IN NITELLA : I. APPLICATIONS OF LIKE SOLUTIONS.

Experiments on cutting confirm the prediction that the current of injury will be positive when the cell is in contact with concentrated solutions and negative with dilute solutions. They support the idea that the protoplasm is made up of layers differing considerably in their properties, each having a death curve of simple and regular form, the more rapid alteration of the outer layer making the protoplasm more positive and the more rapid alteration of the inner making it more negative. From the point where the cell is cut a wave of some sort, which we may for convenience call a death wave, passes along the cell, setting up at each point it touches a death process which has the greater speed and intensity the nearer it is to the cut.     

STUDIES OF THE INNER AND OUTER PROTOPLASMIC SURFACES OF LARGE PLANT CELLS : II. MECHANICAL PROPERTIES OF THE VACUOLAR SURFACE

The vacuolar surface of Nitella is covered with a non-aqueous film too thin to be visible as a separate membrane. The motion of the protoplasm may subject this film to a good deal of mechanical disturbance. Apparently this does not rupture the film for no dye escapes into the protoplasm as the result of such disturbance when the vacuolar sap is deeply stained with neutral red or brilliant cresyl blue. When the deeply stained central vacuole breaks up into several smaller vacuoles, leaving the outer protoplasmic surface in its normal position, there is no evidence of the escape of dye into the protoplasm through the film surrounding the vacuole.     

Thrombospondin promotes process outgrowth in neurons from the peripheral and central nervous systems.

Thrombospondin (TSP) is a prominent constituent of the extracellular matrix of the developing nervous system. We have examined the effects of TSP on the morphological differentiation of neurons. In short-term cultures (less than or equal to 24 hr) of embryonic rat sympathetic neurons, TSP stimulated neurite outgrowth, causing significant increase in the number of processes and their length. Similar effects were observed in cultures of rat dorsal root ganglion, hippocampal, and cerebral cortical neurons. Moreover, in cultures of central neurons, TSP was more effective than laminin in enhancing process extension. Analysis of long-term (5-7 days) cultures of sympathetic neurons indicated that processes formed in the presence of TSP had the cytochemical characteristics of axons. Thus, TSP can influence neuronal development by selectively enhancing axonal growth. The neurite-promoting region of the molecule was identified using a panel of monoclonal antibodies targeted to different regions of the protein. Process outgrowth could be totally inhibited with antibody A4.1, which recognizes the stalk region of TSP. These data suggest that the neurite-promoting activity is localized to a single region of the TSP molecule.     

THE ACCUMULATION OF ELECTROLYTES : I. THE ENTRANCE OF AMMONIA INTO VALONIA MACROPHYSA

When 0.005 M NH₄Cl is added to sea water containing cells of Valonia macrophysa ammonia soon appears in the sap and may reach a concentration inside over 40 times as great as outside. It appears to enter as undissociated NH₃ (or NH₄OH) and tends to reach a pseudoequilibrium in which the activity of undissociated NH₃ (or NH₄OH) is the same inside and outside. When ammonia first enters, the pH value of the sap rapidly rises but it soon reaches a maximum and subsequently falls off. At the same time there is an increase of halide in the sap which, however, does not run a parallel course to the ammonia accumulation, but it comes to a new equilibrium value and remains constant. The increase in NH₃ in the sap is accompanied by a decrease in the concentration of K. As NH₃ enters the specific gravity of the sap decreases and the cells rise to the surface and continue to grow as floating organisms. The growth of the cells is increased.