Journal Article

Changes in the Apoplastic pH Are Involved in Regulation of Xyloglucan Breakdown of Azuki Bean Epicotyls under Hypergravity Conditions

Kouichi Soga, Kazuyuki Wakabayashi, Takayuki Hoson and Seiichiro Kamisaka

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 41, issue 4, pages 509-514
Published in print April 2000 | ISSN: 0032-0781
Published online April 2000 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/41.4.509
Changes in the Apoplastic pH Are Involved in Regulation of Xyloglucan Breakdown of Azuki Bean Epicotyls under Hypergravity Conditions

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Hypergravity inhibited elongation growth of azuki bean (Vigna angularis Ohwi et Ohashi) epicotyls by decreasing the mechanical extensibility of cell walls via the increase in the molecular mass of xyloglucans [Soga et al. (1999) Plant Cell Physiol. 40: 581]. Here, we report that the pH value of the apoplastic fluid in epicotyls increased from 5.8 to 6.6 by hypergravity (300 × g) treatment. When the xyloglucan-degrading enzymes extracted from cell walls of the 1 × g control epicotyls were assayed in buffer at pH 6.6 and 5.8, the activity at pH 6.6 was almost half of that at pH 5.8. In addition, when enzymically active cell wall preparations obtained from 1 × g control epicotyls were autolyzed in buffer at pH 5.8 and 6.6 and then xyloglucans were extracted from the autolyzed cell walls, the molecular mass of xyloglucans incubated at pH 5.8 decreased during the autolysis, while that at pH 6.6 did not change. Thus, the xyloglucans were not depolymerized by autolysis at the pH value (6.6) observed in the hypergravity-treated epicotyls. These findings suggest that in azuki bean epicotyls, hypergravity decreases the activities of xyloglucan-degrading enzymes by increasing the pH in the apoplastic fluid, which may be involved in the processes of the increase in the molecular mass of xyloglucans, leading to the decrease in the cell wall extensibility.

Keywords: Apoplastic pH; Azuki bean (Vigna angularis); Cell wall extensibility; Hypergravity; Molecular mass; Xyloglucans

Journal Article.  0 words. 

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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