Biomedical subjects

Teruo Shimmen

Publications and source records attributed to Teruo Shimmen.

24 records · Page 2Linked to original sources

PubMed2003

Studies on mechano-perception in the Characeae: transduction of pressure signals into electrical signals.

Mechano-perception by Chara cells was studied with an emphasis on the role of the nodal complex in transducing pressure signals into electrical signals. Three types of experimental material were used: (1) tandem internodal cells connected by a single layer of nodal cells; (2) single internodal cells, from which either apical or basal nodes were removed by ligation and cutting; (3) single internodes from which both nodes had been removed. Exposure to a hypertonic solution (sorbitol or sucrose) induced a depolarization at the node in 1 and 2. Depolarization did not occur at the ligated end of the cell in 2, or at all in 3. Addition of K+ increased the magnitude of the response, whilst it was significantly decreased by the divalent cations, Ca2+ and Mg2+. Electrical resistance decreased at the node during the depolarization, showing that a passive diffusion potential was responsible. I suggest that the change in the trans-nodal hydraulic pressure difference mechanically stretches the plasma membrane, and this induces the electrical depolarization.

Characeae↗

PubMed2003

Synthesis of a callosic substance during rhizoid differentiation in Spirogyra.

Spirogyra living in running water is anchored to the substratum by rhizoids that form at the ends of the filaments. A new terminal cell differentiates into a rhizoid cell if the filament is injured. The mode of growth changes from diffuse to tip growth when rhizoid differentiation begins. In this study, we found that a callosic substance was synthesized during rhizoid differentiation. Decreasing the cell turgor, lowering extracellular Ca2+ or adding Gd3+, all inhibited the commencement of rhizoid differentiation as well as synthesis of the callose-like substance at the tip of the terminal cell. A callosic substance was also synthesized during formation of the conjugation tube.

Calcium↗

PubMed2003

An Arabidopsis ACT2 dominant-negative mutation, which disturbs F-actin polymerization, reveals its distinctive function in root development.

Eight functional actin genes are present in Arabidopsis: The functional characterization of these genes in loss-of-function mutants is difficult, because highly conserved isovariants are generally expressed in the same tissue. We isolated a novel semi-dominant mutant allele (act2-2D) of an actin gene, ACT2, with a missense mutation which causes an amino acid substitution at the surface of the ACT2 protein. ACT2 promoter::ACT2-2D transgenic plants showed the same phenotype as act2-2D, indicating that act2-2D is a dominant-negative mutant. act2-2D exhibited defects in the initiation and elongation of root hairs, the elongation of root epidermal cells, and growth in aerial portions. Specifically, radial cell expansion was reduced and occasional cell death occurred in trichoblasts but not in atrichoblasts of the root epidermis. In contrast, cell division patterns in the root meristem were not affected. act2-3, a loss-of-function ACT2 mutant, did not develop most of these morphological abnormalities. Actin filament (F-actin) bundles in root epidermal cells of act2-2D were shorter than in the wild type and in the loss-of-function mutant. We conclude that defective F-actin polymerization caused the aberrant cell morphology in a dominant-negative manner, and that ACT2 functions in cell elongation and root hair formation.

Actins↗

PubMed2002

Rhizoid differentiation in Spirogyra: position sensing by terminal cells.

Some species of Spirogyra anchor themselves to the substrate by differentiating rhizoids. A rhizoid is differentiated only from the terminal cell, suggesting that this cell can recognize its terminal position in a filament. In the present study, we have analyzed the mechanism for position sensing by the terminal cell. When a filament is cut, a new cell occupies the terminal position, and three phenomena are induced: (1) the cell wall of the cut cell detaches from the new terminal cell; (2) adhesive material is secreted by the terminal cell; and (3) the terminal cell begins to differentiate a rhizoid via tip growth. All of these phenomena were inhibited by adding sorbitol to the external medium, suggesting that turgor pressure is involved in position sensing by the terminal cell. The inhibition by sorbitol was reversible. Upon cutting a filament, the distal end of a new terminal cell became convex. However, when a filament was cut in the presence of sorbitol, the distal end of a new terminal cell became less convex. Either treatment with Gd(3+) or decrease in extracellular Ca(2+) resulted in inhibition of all these phenomena, suggesting possible involvement of stretch-activated ion channel in position sensing by terminal cells.

Calcium↗

PubMed2002

Induction of a new alkaline band at a target position in internodal cells of Chara corallina.

Characean cells develop alternating alkaline and acid bands on their surface upon illumination. However, the mechanism of band formation is not fully understood. In the present study, we succeeded in inducing a new alkaline band at an original acid band in internodal cells of Chara corallina. Chloroplasts in an acid band were locally removed by wounding the cell in the absence of the cell turgor pressure. The chloroplast-removed area was observed as a white belt in a green cylindrical internodal cell. This internodal cell developed a new alkaline band on the surface at the chloroplast-removed area. The narrower the chloroplast-removed area, the less significant the extent of OH(-) extrusion. This is the first success in inducing a new alkaline band at a target position in Characeae.

Aluminum↗

PubMed2002

Electrical perception of "death message" in chara: analysis of rapid component and ionic process.

Electrical response upon wounding was analyzed in Chara corallina. A specimen comprising two adjoining internodal cells was prepared. One cell (victim cell) was killed by cutting and any changes in the membrane potential of the neighboring cell (the receptor cell) were measured. Upon cutting the victim cell, the receptor cell generated four kinds of depolarizations: (1) rapid component, (2) slow and long-lasting component, (3) action potential and (4) small spike. Rapid and slow components were observed in most cells. On the other hand, the action potential and small spike were not always ubiquitous among specimens. When an action potential was generated just after cutting the victim cell, the rapid component could not be observed due to masking by the action potential. It was suggested that both rapid and slow components were generated at the nodal end. On the other hand, action potentials were thought to be generated at the flank of the receptor cell. High turgor pressure of the cell was necessary for generating both rapid and slow components. Experiments under K(+)-induced depolarization unequivocally showed that the Cl(-) channel at the nodal end of the receptor cell was activated upon cutting the victim cell.

Calcium↗