Fucosylated high molecular mass but not non-fucosylated low molecular mass xyloglucans undergo an extensive depolymerization in cell walls of azuki bean epicotyls.
Epicotyl cuttings of azuki bean were incubated with [14C]-glucose (Glc) or [3H]-fucose (Fuc), and the metabolism of radiolabeled polymers in the 24% KOH-extractable cell wall fraction was investigated. Applied 14C-Glc and (3)H-Fuc were predominantly incorporated into the glucan backbone and Fuc residue of xyloglucan molecules, respectively. On gel permeation chromatography, 14C-polymers consisted of a main peak (0.7-1.0 MDa) and shoulder peak (30 kDa). The pattern was similar to that of iodine-reactive xyloglucans in the fraction. On the other hand, 3H-polymers consisted of a single peak eluted around 0.7-1.0 MDa. The elution patterns of 14C- and 3H-polymers were constant during the incubation period, although incorporated radioactivity increased with time. In the pulse-chase experiment, the high molecular mass peaks (0.7-1.0 MDa) of both 14C- and 3H-polymers showed an extensive molecular mass downshift, but not the shoulder peak of 14C-polymers. These results indicate that xyloglucans in the fraction consist of two types of molecules; fucosylated high molecular mass polymers and non-fucosylated low molecular mass polymers. Azuki bean epicotyls may synthesize both types of xyloglucans independently, but only fucosylated xyloglucans undergo an active depolymerization in the cell wall.
Arai
Kuninori
K
Department of Biological Sciences, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka 558-8585, Japan.
Wakabayashi
Kazuyuki
K
Soga
Kouichi
K
Hoson
Takayuki
T
D002250:Carbon Radioisotopes; D002473:Cell Wall / Q000378:metabolism; D007887:Fabaceae / Q000378:metabolism*; D005643:Fucose / Q000378:metabolism*; D005936:Glucans / Q000737:chemistry* / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism; D006031:Glycosylation; D008970:Molecular Weight; D018520:Plant Shoots / Q000378:metabolism; D014316:Tritium; D014990:Xylans / Q000737:chemistry* / Q000378:metabolism*
D002250:Carbon Radioisotopes; D005936:Glucans; D014990:Xylans; D014316:Tritium; D005643:Fucose; C029353:xyloglucan; D005947:Glucose