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Biomedical subjects

B G Pickard

Publications and source records attributed to B G Pickard.

27 records · Page 2Linked to original sources
PubMed1986

Evaluation of ethylene as a mediator of gravitropism by tomato hypocotyls.

Assessments of the participation of ethylene in gravitropism by hypocotyls of tomato (Lycopersicon esculentum Mill.) indicate that gravitropism can occur without substantial change in ethylene production. Moreover, lowering or evaluating ethylene over a considerable range, as well as inhibiting ethylene action, fails to influence gravitropic bending. This vitiates the possibility that ethylene is a mediator of the primary, negative gravitropic response of tomato shoots.

Amino Acids↗
PubMed1984

Burst of ethylene upon horizontal placement of tomato seedlings.

Seedlings of Lycopersicon esculentum Mill. cv Rutgers emit a pulse of ethylene during the first 2 to 4 minutes following horizontal placement. Because this burst appears too rapid and brief to be mediated by increase in net activity of 1-aminocyclopropane-1-carboxylic acid synthase, it might result form accelerated transformation of vacuolar 1-aminocyclopropane-1-carboxylic acid to ethylene.

Amino Acids↗
PubMed1984

Voltage transients elicited by brief chilling.

Chilling auxin-depleted, etiolated stems of Pisum sativum L. to 4 degrees C for 60 s enhanced the production of previously described voltage transients 20-fold. It is postulated that plasmalemmal permeability to Ca2+ is increased at low temperature, permitting influx of the ion from the apoplast to the cytosol and thereby promoting production of transients. Heating to 40 degrees C or 45 degrees C elicits no increase in transients, and heating to 50 degrees C leads to loss of turgor.

Biological Transport↗
PubMed1984

Voltage transients elicited by sudden step-up of auxin.

It is hypothesized (i) that the molecular mechanism for the reception of friction and flexure and the mechanism by which auxin enhances ethylene production have in common a release of free calcium into the cytosol, (ii) that elevated cytosolic calcium initiates vesicle exocytosis, and (iii) that the vesicles release a factor or set of factors which depolarizes the plasmalemma and promotes ethylene synthesis. One consequence of such exocytosis should be small, extracellularly observable voltage transients. Transients, ranging in size up to 600 microvolts and possessing risetimes (10-90%) of approximately 200 ms, are known to be elicited in etiolated stems of Pisum sativum L. by friction and are here shown to be elicited by sudden increase of auxin concentration and also by a Ca2+ ionophore.

Calcimycin↗
PubMed1966

Geotropic response of wheat coleoptiles in absence of amyloplast starch.

Young coleoptiles of wheat (Triticum durum var. Henry), depleted of amyloplast starch by incubation at 30 degrees C with gibberellin plus kinetin, retained their geotropic responsiveness. Depleted coleoptiles curved upward more slowly than controls, but this was commensurate with their slower growth. The ratio of curvature to growth was about 50 degrees per mm of elongation in both cases. Newly excised coleoptiles, though containing much more starch than incubated controls, curved only about 25 degrees per mm. The tissue treated in gibberellin plus kinetin appeared to contain no starch when examined (a) freshly squashed, (b) as fixed material sectioned thin and stained by the PAS procedure, and (c) as electron micrographs. Shrunken, starch-free amyloplasts could be identified in certain regions, but these did not show evidence of asymmetric distribution under the influence of gravity. The possibilities that other organelles function as statoliths are considered, and it is concluded not only that georeception is independent of starch grains, but further that it may not be due to statoliths at all in an ordinary sense.

Gibberellins↗
PubMedDate not supplied

Arabinogalactan protein and wall-associated kinase in a plasmalemmal reticulum with specialized vertices.

Arabinogalactan protein and wall-associated kinase (WAK) are suspected to be regulatory players at the interface between cytoplasm and cell wall. Both WAK(s) and arabinogalactan shown likely to represent arabinogalactan protein(s) have been visualized there with computational optical-sectioning microscopy. The arabinogalactan occurs in a polyhedral array at the external face of the cell membrane. WAK, and other proteins as yet unidentified, appear to fasten the membrane to the wall at vertices of the array. Evidence is presented that the array bears an important part of the mechanical stress experienced by the membrane, and it is speculated that the architectural organization of arabinogalactan protein, WAK, and other components of the array is critical for coordination of endomembrane activities, growth, and differentiation. The array has been named the plasmalemmal reticulum.

Antibodies, Monoclonal↗