title: Germanium does not substitute for boron in cross-linking of rhamnogalacturonan II in pumpkin cell walls.
abstract: Boron (B)-deficient pumpkin (Cucurbita moschata Duchesne) plants exhibit reduced growth, and their tissues are brittle. The leaf cell walls of these plants contain less than one-half the amount of borate cross-linked rhamnogalacturonan II (RG-II) dimer than normal plants. Supplying germanium (Ge), which has been reported to substitute for B, to B-deficient plants does not restore growth or reduce tissue brittleness. Nevertheless, the leaf cell walls of the Ge-treated plants accumulated considerable amounts of Ge. Dimeric RG-II (dRG-II) accounted for between 20% and 35% of the total RG-II in the cell walls of the second to fourth leaves from Ge-treated plants, but only 2% to 7% of the RG-II was cross-linked by germanate (dRG-II-Ge). The ability of RG-II to form a dimer is not reduced by Ge treatment because approximately 95% of the monomeric RG-II generated from the walls of Ge-treated plants is converted to dRG-II-Ge in vitro in the presence of germanium oxide and lead acetate. However, dRG-II-Ge is unstable and is converted to monomeric RG-II when the Ge is removed. Therefore, the content of dRG-II-Ge and dRG-II-B described above may not reflect the actual ratio of these in muro. (10)B-Enriched boric acid and Ge are incorporated into the cell wall within 10 min after their foliar application to B-deficient plants. Foliar application of (10)B but not Ge results in an increase in the proportion of dRG-II in the leaf cell wall. Taken together, our results suggest that Ge does not restore the growth of B-deficient plants.
authors.affiliation: National Agricultural Research Center for Kyushu Okinawa Region, Nishigoshi, Kumamoto 861-1192, Japan. tishii@ffpri.affrc.go.jp
authors.forename: Tadashi
authors.initials: T
authors.lastname: Ishii
authors.forename: Toshiro
authors.initials: T
authors.lastname: Matsunaga
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Iwai
authors.forename: Shinobu
authors.initials: S
authors.lastname: Satoh
authors.forename: Junji
authors.initials: J
authors.lastname: Taoshita
mesh_terms: D001888:Boric Acids / Q000494:pharmacology; D001895:Boron / Q000172:deficiency / Q000378:metabolism / Q000494:pharmacology*; D002473:Cell Wall / Q000187:drug effects / Q000378:metabolism*; D028464:Cucurbita / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D005857:Germanium / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D010368:Pectins / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism
chemical_list: D001888:Boric Acids; C042492:rhamnogalacturonan II; D005857:Germanium; C040516:germanium oxide; D010368:Pectins; D001895:Boron; C032688:boric acid