Auxin and Fusicoccin Enhancement of β-Glucan Synthase in Peas

Abstract

Fusicoccin (FC), like indoleacetic acid (IAA), causes Golgi-localized B-1,4-glucan synthase (GS) activity to increase when applied to pea third internode segments whose GS activity has declined after isolation from the plant. This suggests that GS activity is modulated by H' extrusion; in agreement, vanadate and nigericin inhibit the GS response. The GS response is not due to acidification of the cell wall. Treatment of tissue with heavy water, which in effect raises intracellular pH, mimics the MATERIALS AND METHODS Pea (Pisum sativum cv Alaska) seedlings were grown and third internode segments 8 mm long were cut as described (27), except that for all experiments other than that ofTable I, each internode was abraded (14) by stroking with an aqueous paste of No. 305 emery powder (Edmund Scientific, Barrington, NJ) which was then rinsed off by vigorous agitation in water, before cutting the segment. The segments were kept 2 to 3 h at 35C in moist air to deplete their GS activity (27).Lots of 30 segments, each in a small Stender dish, were pretreated usually for 30 to 60 min at 35°C in a medium containing 30 mm sucrose, 0.8 mm citric acid/Pipes (Tris salt) buffer pH 6.5 (unless specified otherwise in figure or table legends), containing usually 1 mM KCI, plus indicated additions. This pretreatment medium was removed and 2.0 ml of a similar incubation medium, with or without IAA or FC as indicated, the initial pH of which had been carefully measured to 0.01 pH unit with a semimicro glass electrode, were added, and the dishes were kept normally at 35C for 60 or 90 min (the incubation period). The incubation medium was removed and its pH was remeasured, while the segments were rinsed with ice water and held on ice until they were homogenized to prepare membranes for enzyme assay. H+ extrusion was estimated from the measured drop in pH (ApH) of the medium during incubation, using the postincubation titration curve

Hormonal and Gravitropic Specificity in the Regulation of Growth and Cell Wall Synthesis in Pulvini and Internodes from Shoots of Avena sativa L. (Oat)

“…The stimulation of pulvinar cell wall synthesis by FC is similar to the findings of Brummell and Hall (1983) in elongating, auxin-responsive pea stem segments, in which the effect is apparently mediated at least in part by increased activity of glucan synthase (Ray, 1985(Ray, ,1987. In the present work, FC stimulated incorporation predominately into the matrix (TFA soluble) component of the wall, whereas IAA and gravistimulus promoted incorporation proportionally into both fractions (Figs.…”

The rhd6 Mutation of Arabidopsis thaliana Alters Root-Hair Initiation through an Auxin- and Ethylene-Associated Process

“…The phenocopy of the rhd6 mutant phenotype by AVG-treated wild-type seedlings is consistent with a role for ethylene in the assembly of the, root-hair initiation complex. Although the precise role of aurin in roothair initiation is not clear, auxin has been implice ted in the loosening of cell walls (Vanderhoef and Dute, L981), the altered expression of cell wall components (Nishitani and Masuda, 1983;Ray, 1985), and the polarization of tissues (Sachs, 1984(Sachs, , 1991.…”

ATP‐driven Ca2+ transport in sealed plasma membrane vesicles prepared by aqueous two‐phase partitioning from leaves of Commelina communis

“…Glucan synthase I (EC 2.4.1.29) activity was measured as glucose incorporation from UDP-D-[U-'*C]glucose into alkaline-insoluble glucan at low substrate levels (60 \iM) and high Mg^* concentration (20 mM) in the presence of 0.02% (v/v) Triton X-100 (Ray 1985). Glucan synthase II (EC 2.4.1.34) activity was measured as glucose incorporation into ethanol-insoluble glucan from UDP-D-[U-'''C]-glucose at high substrate levels (0.5 mM) iti the presence of 0,02% (v/v) Tritoti X-100 (VanDerWoude et al 1974, Pierce andHendrix 1979).…”