Sugar uptake by cotton tissues: leaf disc versus cultured roots

The synthesis, transport, and posttranslational processing of reserve globulin in Avena sativa L. seeds were studied by pulse-chase labeling. Developing oat seeds were labeled with radioactive sulfate and tissue homogenates were used for globulin extraction.

Two globulin precursors (58-62 kilodaltons) were labeled after 1 hour pulse. The α and β globulin subunits appeared between 2 and 10 hours later, while simultaneously the 58 to 62 kilodaltons polypeptides gradually disappeared. This confirmed a precursor-product relationship. In a second pulse-chase experiment, the tissue extracts were fractionated on a sucrose gradient. The major portion of radioactivity was initially (1 hour pulse) associated with the endoplasmic reticulum. However, a significant amount of radioactivity shifted from the endoplasmic reticulum to protein bodies after 20 hours chase, suggesting the transport of the newly synthesized proteins. Protein bodies isolated from pulse-chased seeds were analyzed for the arrival of the newly synthesized globulin. Labeled precursors were detected after 2 hours chase and gradually disappeared. The α and β subunits appeared during the same chase period and assembled into a 12S oligomer.

The data indicated that oat globulin was synthesized as two large precursors which were transported from endoplasmic reticulum into protein bodies where they were processed to the α and β subunits forming a 12S oligomer.

     

Effect of Salinity upon Cell Membrane Potential in the Marine Halophyte, Salicornia bigelovii Torr

The electrophysiology of root cells of the marine halophyte, Salicornia bigelovii Torr., has been investigated. Cellular concentrations of K⁺, Cl⁻, and Na⁺ and resulting cell membrane potentials were determined as functions of time and exposure to dilutions of artificial seawater. Treatment of these data by the Nernst criterion suggests that Cl⁻ is actively transported into these root cells, but that active transport need not be invoked to explain the accumulation of Na⁺ at all salinities investigated nor for K⁺ at moderate to high salinities. In low environmental salinity, the cell electropotential of Salicornia root cells was found to respond to inhibitors in a fashion similar to that observed in glycophytes; in high environmental salinity, root cell membrane potential appears to be insensitive to bathing salinity and m-chlorocarbonylcyanide phenylhydrazone induces membrane hyperpolarization, in contrast to the response of glycophytes to such treatments. The fact that measured membrane potentials exceed diffusion potentials for Na⁺, K⁺, and Cl⁻ and the observation of a rapid depolarization by CO in the dark suggests an electrogenic component in Salicornia root cell membrane potentials.     

Nuclear Magnetic Resonance Studies of Sodium and Potassium in Etiolated Pea Stem

Based on nuclear magnetic resonance (NMR) spectroscopy and other evidence, it has been argued that tissues accumulate, and retain, ions in a binding process by a highly structured water-protoplasm system; thus active membrane transport need not be involved. Recent evidence has accounted for the loss of resonance intensity usually found when investigating quadrupolar ions in animal tissue. Using continuous wave NMR spectroscopy, we have examined two quadrupolar ions, Na⁺ and K⁺, in pea stem cells where about 90% of the ion content is in the largely aqueous vacuoles having a membrane barrier. The NMR resonances from these ions correspond to almost 100% of that expected from independent measurements of total ion content. This indicates that the ions are retained as free ions after accumulation. The small fraction which is NMR invisible may represent ions in an ordered, anisotropic environment, such as that in the wall or cytoplasm.     

Translocation of sucrose by squash plants

Sucrose-¹⁴C was fed to the leaf blades of squash plants (Cucurbita pepo L. var. melopepo torticallis Bailey) for 30 or 60 minutes. Petioles of treated plants were cut into sections and extracted. The majority of the ¹⁴C within the petiole was in sucrose rather than stachyose, the sugar that is transported by the squash plants when ¹⁴CO₂ is supplied. This indicates that the phloem loading system of squash plants is not the system that specifies which sugar is transported.     

Labeling pattern of translocated stachyose in squash

One mature blade of each squash plant was continuously labeled with ¹⁴CO₂ for 15, 30, or 70 minutes in light. The ethanol soluble materials from serial sections of petioles were extracted and separated by paper chromatography. The ratios of label in the various components of this fraction were determined. Stachyose, which contained the major portion of the label of this fraction, was hydrolyzed and the resultant hydrolysate was separated by paper chromatography. Specific activities of the hexoses derived from stachyose were determined. It was found that the glucose and fructose moieties of stachyose became labeled at the same rates; however, the galactose moiety became labeled more rapidly.     

Human colon carcinoma cells with increased invasive capacity obtained by selection for sialyl-dimeric LeX antigen.

Sialyl-dimeric LeX antigen (NeuAc alpha 2-3Gal beta 1-4[Fuc-alpha 1-3] GlcNAc beta 1-3Gal beta 1-4[Fuc alpha 1-3]GlcNAc beta 1-R; SLX) is an oncodevelopmental carbohydrate antigen expressed both on glycolipids and on mucin-like glycoproteins in human colorectal carcinomas. The levels are higher in primary tumors at advanced stages than in tumors at early stages, and metastatic lesions contain a greater quantity of this antigen than corresponding primary tumors. To study whether this antigen influences the metastatic behavior of tumor cells, we selected SLX variant cells from the human colon carcinoma cell line KM12C using the specific monoclonal antibody FH6. We obtained two stable cell lines: a high expresser (KM12-HX) and a low expresser (KM12-LX) of this antigen. The growth rate of these cells are similar. A mucin-like glycoprotein reactive with monoclonal antibody FH6 was detected after electrophoretic separation of KM12-HX cell lysates but not of KM12-LX lysates. The degree of invasion was compared in assays in vitro using matrigel-coated filter membranes. The number of KM12-HX cells that invaded the membranes was significantly higher than KM12-LX cells.     

The B66.0 protein of Escherichia coli is the product of the dnaK+ gene

B66.0 is one of the most abundant proteins of Escherichia coli. Its relative rate of synthesis is highly regulated depending on temperature and the growth rate of the culture. We identified the B66.0 protein to be the dnaK+ structural gene product since dnaK756 mutant bacteria synthesized a B66.0 protein with a more acidic isoelectric point.     

Effect of bacteriophage lambda infection on synthesis of groE protein and other Escherichia coli proteins.

We used two-dimensional gel electrophoresis to quantitate the changes in rates of synthesis that follow phage lambda infection for 21 Escherichia coli proteins, including groE and dnaK proteins. Although total protein synthesis and the rates of synthesis of most individual E. coli proteins decreased after infection, some proteins, including groE protein, dnaK protein, and stringent starvation protein, showed increases to rates substantially above their preinfection rates. Infection by lambda Q- affected host synthesis in the same way as infection by gamma+, whereas infection by lambda N- showed no detectable effect on host synthesis. Deletion of the early genes between att and N abolished the effect, and shorter deletions in this region gave intermediate effects. By this sort of deletion mapping, we show that a large part, though not all, of the effect of lambda infection on host protein synthesis can be ascribed to the early region that contains phage genes Ea10 and ral. We compared the changes in protein synthesis after infection with the changes that occur in uninfected cells upon heat shock or amino acid starvation. The spectrum of changes that occurred on infection was very different from that seen after heat shock but quite similar to that seen during amino acid starvation. Despite this similarity of the effects of lambda infection and starvation, we did not detect any increase in the level of guanosine tetraphosphate during infection. We show that the groE protein is the same protein as B56.5 of Lemaux et al. (Cell 13:427-434, 1978) and A protein of Subramanian et al. (Eur. J. Biochem. 67:591-601, 1976).