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Promotion of elongation and acid invertase activity in Phaseolus vulgaris L. internode segments by phenylacetic acid (1990)

Small, David K. ; Morris, David A.

Springer

Plant growth regulation 9 (1990), S. 329-340

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ISSN: 1573-5087

Keywords: acid invertase (EC 3.2.1.26) ; auxin (cell elongation) ; indol-3yl-acetic acid (IAA) ; N-1-naphthylphthalamic acid (NPA) ; Phaseolus vulgaris L. ; phenylacetic acid (PAA) ; stem elongation

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract Phenylacetic acid (PAA) significantly stimulated the elongation of isolated Phaseolus vulgaris internodal segments and prevented the decline in acid invertase specific activity observed in segments incubated in the absence of growth substances. Unlike IAA, which stimulated both elongation and invertase activity over a very wide range of concentrations (〈10-4 - 1 mol.m-3; optimum 10-2 mol.m-3), the response to PAA was restricted to a much narrower range of concentrations (3 × 10-2 - 1 mol.m-3; optimum ca. 1–2 × 10-1mol.m-3). At the optimum concentration of PAA, the stimulation of both responses was about 63–75% of that induced by the optimum concentration of IAA. The differences in the concentration range and magnitude of the responses to IAA and PAA were not due to differences in uptake of the two compounds. The stimulation of elongation by both compounds was prevented by 3.6 × 10-2mol.m-3 cycloheximide (CH), and acid invertase activites were greatly reduced compared with samples treated with growth substances alone. A saturating concentration of the specific auxin efflux carrier inhibitor N-1-naphthylphthalamic acid (NPA) slightly promoted the growth of control segments, probably by reducing the loss of residual endogenous auxin to the incubation medium. The elongation induced by PAA at its optimum concentration was considerably greater than the elongation induced by NPA, indicating that PAA did not cause growth by preventing the loss of endogenous auxin from the segments. Elongation responses to combinations of IAA and PAA suggested that the compounds were acting additively and that they were affecting growth by the same mechanism.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00024918

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Expression of dimeric and tetrameric acetylcholinesterase isoforms on the surface of cultured bovine adrenal chromaffin cells (1994)

Michaelson, Samantha ; Small, David H. ; Livett, Bruce G.

New York, N.Y. : Wiley-Blackwell

Journal of Cellular Biochemistry 55 (1994), S. 398-407

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ISSN: 0730-2312

Keywords: protein transport ; chromaffin cell ; organophosphorus ; GPI-linked ; phosphatidyl-inositol-specific phospholipase C ; Life and Medical Sciences ; Cell & Developmental Biology

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Chemistry and Pharmacology , Medicine

Notes: Acetylcholinesterase is a highly polymorphic enzyme, which can be anchored to the cell surface through several different mechanisms. Dimeric (G2) acetylcholinesterase isoforms are attached by a glycosylphosphatidyl-inositol (GPI) linkage, whereas tetrameric (G4) forms are linked through a 20 kilodalton hydrophobic subunit. Although cells of haemopoietic origin contain large amounts of G2 GPI-linked acetylcholinesterase, most tissues express only trace amounts of this isoform. We examined the expression of acetylcholinesterase isoforms in cultured bovine adrenal medullary chromaffin cells. Two major isoforms (G2 and G4) were identified on the cell surface. The G2 isoform, which accounted for approximately half the cell-surface enzyme activity, was linked to the membrane through a GPI anchor. After treatment with diisopropylfluorophosphate to completely inhibit cellular acetylcholinesterase, the G4 isoform was found to be resynthesised and transported to the cell surface more rapidly than the G2 isoform. As the addition of GPI anchors is known to be a very rapid step, this finding suggested that the G2 and G4 isoforms might be transported to the cell surface by two different mechanisms. This conclusion was supported by results from subcellular fractionation experiments. The ratio of G4/G2 membrane-bound acetylcholinesterase varied between different subcellular fractions. The membrane-bound G2 isoform was greatly enriched in a high-speed “microsomal” fraction. G4 acetylcholinesterase is known to be actively secreted by chromaffin cells in culture. Although the G4 isoform was present on the cell surface, most of the secreted enzyme was derived from an intracellular pool. Thus, it is unlikely that the cell-surface G4 isoform contributes significantly to the pool of secreted enzyme. Instead, the expression of two different membrane-bound isoforms may provide a means by which chromaffin cells can target the enzyme to different locations on the cell surface. © 1994 Wiley-Liss, Inc.

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