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Biomedical subjects

B Rubinstein

Publications and source records attributed to B Rubinstein.

53 records · Page 3Linked to original sources
PubMed1978

Use of lipophilic cations to measure the membrane potential of oat leaf protoplasts.

Uptake of the lipophilic cation triphenylmethylphosphonium into mesophyll protoplasts of oat (Avena sativa L. cv. "Garry") approaches equilibrium at 3 to 4 hours. The resulting external and internal concentrations are then used with the Nernst equation to obtain a membrane potential of -62 millivolts, inside negative. Potentials calculated in this manner are depolarized by adding 2 mm sodium azide and 50 mum carbonyl cyanide m-chlorophenylhydrazone as well as by increasing the external proton and potassium concentrations. The depolarizations are qualitatively similar to those seen when oat mesoyphll cells are measured in situ with microelectrodes. It is concluded that due to the lack of turgor and fragility of protoplasts, estimations of their membrane potential may be made more reliably, under some conditions, with lipophilic cations than with microelectrodes.

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PubMed1977

Effects of Osmotic Shock on Some Membrane-regulated Events of Oat Coleoptile Cells.

Oat coleoptile sections (Avena sativa L. cv. "Garry") were osmotically shocked with 0.5 m mannitol followed by 1 mm Na-phosphate (pH 6.4) at 4 C. This treatment reduced uptake of alpha-aminoisobutyric acid, 3-o-methyl glucose, and leucine by 75 to 90% but inhibited (36)Cl(-) uptake only 30%. Some recovery was observed 1 to 3 hours later. Respiration rates were unaffected by osmotic shock and protein synthesis was reduced 11%.Osmotic shock also stimulated efflux of alpha-aminoisobutyric acid and K(+) and led to an increase in conductivity of the solution bathing shocked sections. The transmembrane electropotential of 75% of the shocked cells fell to -20 mv to -45 mv compared with the majority of unshocked cells at -80 mv to -120 mv.We concluded that osmotic shock selectively modifies the plasma membrane. The inhibitions of uptake could be due to removal of specific components of the plasma membrane and/or to the lowered electropotential.

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PubMed1977

Osmotic Shock Inhibits Auxin-stimulated Acidification and Growth.

Cells of oat coleoptiles (Avena sativa L. cv. "Garry") have been osmotically shocked in order to observe the effect of alterations of the plasma membrane on some auxin responses. When coleoptile sections were treated sequentially with 0.5 m mannitol and 1 mm Na-phosphate (pH 6.4) at 4 C, polar auxin transport and acidification by 1 mM CaCl(2) were unaffected, but auxin-stimulated acidification and growth were eliminated. Shock treatment also had no effect on acid-stimulated growth or on freezing point depression by the cytoplasm. It is suggested that osmotic shock modifies a portion of the plasma membrane which interacts with auxin and eventually leads to growth.

Journal Article↗
PubMed1977

Endothelial cell loss and corneal thickness after intracapsular extraction and iris clip lens implantation: a randomised controlled trial (interim report).

Patients in a randomised controlled trial were chosen either to have iris clip lens implantation after intracapsular cataract extraction or intracapsular extraction only. They were assessed in terms of corneal thickness, postoperative epithelial oedema, and endothelial cell counts. All patients had 1 eye submitted to operation, which was carried out by the same surgeon. There was significantly greater increase in corneal thickness (P less than 0.05) on the 5th postoperative day in eyes which had lens implants (23 patients with intracapsular extraction and 19 with implant), but the difference between the 2 groups became insignificant at 1 month (17 patients in each group). Daily corneal thickness measurements and observations of epithelial oedema in a subgroup (20 patients divided equally into 2 groups) showed that postoperatively there was greater and more widespread corneal oedema after implant surgery. When the operated eye was compared with the unoperated eye, endothelial cell loss was significantly greater in those with implants (P less than 0.01) than in those with simple intracapsular extraction.

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PubMed1977

Corneal oedema and endothelial cell loss after iris-clip lens implantation.

Lens implantation as a form of replacement surgery has some clear advantages over other forms of aphakic correction. The most feared complication of this type of operation is bullous keratopathy. A short-term study was carried out in two comparable groups of patients to assess corneal oedema and endothelial cell loss after simple cataract extraction and after iris-clip lens implantation following intracapsular extraction as a primary procedure. All patients were randomly chosen to have one or other procedure. The results indicate that lens implantation causes greater postoperative corneal oedema and greater endothelial cell loss. It is therefore important for implant surgeons to bear in mind the possible harm they may be inflicting and the need both for stringent criteria of selection and for the adoption of techniques which will minimize endothelial trauma.

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PubMed1977

Corneal edema: iris-clip lens implantation and simple intracapsular extraction compared.

Corneal edema following intracapsular lens extraction and iris-clip lens implantation was compared by assessing corneal thickness and epithelial edema. In a retrospective study the corneal thickness of twenty patients who had intracapsular lens extraction in one eye only was compared with twenty-six patients with iris-clip lens implants in one eye. There was no significant increase in corneal thickness in the operated eye in either group. In a prospective randomized controlled study, a smaller number of patients, had serial measurements of corneal thickness pre- and postoperatively. There was an increase in thickness in the immediate postoperative period for both groups. However, there was no significant difference between eyes which had simple extraction and those which had implants. The implanted eyes however had greater mean increase endothelial trauma in the initial period, compared to eyes with cataract extraction alone.

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PubMed1974

Effect of pH and Auxin on Chloride Uptake into Avena Coleoptile Cells.

The effect of pH on (36)Cl(-) movement into coleoptile cells (Avena sativa L. cv. Garry) was investigated and compared with effects of indoleacetic acid. (36)Cl(-) uptake, but not efflux, is stimulated when coleoptile sections are placed in media adjusted to pH levels from 5 to 3 after a preincubation period at pH 6.5. The enhancement is seen within 2 minutes, is not correlated with growth, and is completely erased by respiratory inhibitors. In comparison to the acid-induced stimulation, the stimulatory effect of indoleacetic acid on (36)Cl(-) uptake is also not accompanied by accelerated efflux, and indoleacetic acid does not further stimulate (36)Cl(-) uptake into 1-millimeter sections beyond that seen at pH 3.5 without auxin.

Journal Article↗
PubMed1972

Characteristics of hook formation by bean seedlings.

Explants were isolated from 6-day-old etiolated bean seedlings (Phaseolus vulgaris L. cv. Black Valentine) containing the cotyledons with 4 mm of hypocotyl just below the node and/or the epicotyl. During incubation on distilled water, uneven growth of the hypocotyl or epicotyl occurred resulting in the formation of a hook. The more rapid growth of the side which became convex was not dependent upon the presence of the slower growing concave side. It was concluded that the main axis has an intrinsic capacity for asymmetric growth. The growth leading to hook formation was inhibited by alpha-naphthaleneacetic acid at concentrations above 0.2 milligram per liter.

Journal Article↗
PubMed1971

The Role of Various Regions of the Bean Hypocotyl on Red Light-induced Hook Opening.

Measurement of various zones on the concave half of etiolated Phaseolus vulgaris L. (cv. Black Valentine) hypocotyls has shown that growth at the basal portion of the elbow and the contiguous upper portion of the shank was stimulated earliest by red light. Growth of these two zones was unaffected by the tissue of the convex half but was inhibited by tissue distal to them. The inhibition was alleviated by the continuous presence of shank tissue below the growing zones. Based on cuts made halfway through the hypocotyl at positions above, below, or between the two zones of growth, it is suggested that cells at the inner portion of the upper shank control in some way the light-induced growth of the elbow cells directly above.

Journal Article↗
PubMed1971

Auxin and red light in the control of hypocotyl hook opening in beans.

Evidence is presented to support the suggestion that endogenous auxinlike substances participate in controlling the unbending of the hypocotyl hook of Phaseolus vulgaris L. (cv. Black Valentine). An acidic indole was detected in hook diffusates by fluorometry; triiodobenzoic acid, an inhibitor of auxin transport, prevented red light-induced unbending, and indoleacetic acid can be substituted for tissue just above the elbow region as an inhibitor of opening. Indoleacetic acid also stimulated growth of shank cells, and red light increased the sensitivity of this tissue to the hormone. A small red light-induced stimulation of auxin transport through the inside half of the hypocotyl shank was observed and may be related to light-induced unbending of the hook.

Journal Article↗
PubMed1969

Evidence for bound phytochrome in oat seedlings.

Phytochrome is consistently observed in pellets centrifuged from homogenates of etiolated, 5-day-old oat seedlings. The majority of pigment associated with the pellet cannot be removed by buffer washes, nor can appreciable quantities of additional phytochrome be adsorbed onto the sedimented material. Over 70% of phytochrome in the pellet is released by 1% Triton X-100.Storage at 0 degrees , irradiation by white light, and Triton treatment all cause much greater loss of photoreversibility in pelleted phytochrome than in supernatant phytochrome. We conclude that the phytochrome in the 1500 to 40,000g (30 min) pellet is distinct from the soluble phytochrome in the supernatant.

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