title: Suppression of Hydroxycinnamate Network Formation in Cell Walls of Rice Shoots Grown under Microgravity Conditions in Space.
abstract: Network structures created by hydroxycinnamate cross-links within the cell wall architecture of gramineous plants make the cell wall resistant to the gravitational force of the earth. In this study, the effects of microgravity on the formation of cell wall-bound hydroxycinnamates were examined using etiolated rice shoots simultaneously grown under artificial 1 g and microgravity conditions in the Cell Biology Experiment Facility on the International Space Station. Measurement of the mechanical properties of cell walls showed that shoot cell walls became stiff during the growth period and that microgravity suppressed this stiffening. Amounts of cell wall polysaccharides, cell wall-bound phenolic acids, and lignin in rice shoots increased as the shoot grew. Microgravity did not influence changes in the amounts of cell wall polysaccharides or phenolic acid monomers such as ferulic acid (FA) and p-coumaric acid, but it suppressed increases in diferulic acid (DFA) isomers and lignin. Activities of the enzymes phenylalanine ammonia-lyase (PAL) and cell wall-bound peroxidase (CW-PRX) in shoots also increased as the shoot grew. PAL activity in microgravity-grown shoots was almost comparable to that in artificial 1 g-grown shoots, while CW-PRX activity increased less in microgravity-grown shoots than in artificial 1 g-grown shoots. Furthermore, the increases in expression levels of some class III peroxidase genes were reduced under microgravity conditions. These results suggest that a microgravity environment modifies the expression levels of certain class III peroxidase genes in rice shoots, that the resultant reduction of CW-PRX activity may be involved in suppressing DFA formation and lignin polymerization, and that this suppression may cause a decrease in cross-linkages within the cell wall architecture. The reduction in intra-network structures may contribute to keeping the cell wall loose under microgravity conditions.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka, Japan.
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Wakabayashi
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka, Japan.
authors.forename: Kouichi
authors.initials: K
authors.lastname: Soga
authors.affiliation: Department of Biological Sciences, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Hoson
authors.affiliation: Division of Life Science, Graduate School of Science and Engineering, Saitama University, Sakura-ku, Saitama, Japan.
authors.forename: Toshihisa
authors.initials: T
authors.lastname: Kotake
authors.affiliation: Japan Aerospace Exploration Agency (JAXA), Sengen, Tsukuba, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yamazaki
authors.affiliation: Japan Aerospace Exploration Agency (JAXA), Sengen, Tsukuba, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Higashibata
authors.affiliation: Japan Aerospace Exploration Agency (JAXA), Sengen, Tsukuba, Japan.
authors.forename: Noriaki
authors.initials: N
authors.lastname: Ishioka
authors.affiliation: Japan Space Forum, Kandasurugadai, Chiyoda-ku, Tokyo, Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Shimazu
authors.affiliation: Japan Space Forum, Kandasurugadai, Chiyoda-ku, Tokyo, Japan.
authors.forename: Keiji
authors.initials: K
authors.lastname: Fukui
authors.affiliation: Japan Manned Space Systems Corp., Kawaguchi, Tsuchiura, Japan.
authors.forename: Ikuko
authors.initials: I
authors.lastname: Osada
authors.affiliation: Japan Manned Space Systems Corp., Kawaguchi, Tsuchiura, Japan.
authors.forename: Haruo
authors.initials: H
authors.lastname: Kasahara
authors.affiliation: Advanced Engineering Services Co., Ltd., Takezono, Tsukuba, Japan.
authors.forename: Motoshi
authors.initials: M
authors.lastname: Kamada
mesh_terms: D002473:Cell Wall / Q000378:metabolism* / Q000502:physiology*; D003373:Coumaric Acids / Q000378:metabolism*; D008031:Lignin / Q000378:metabolism; D012275:Oryza / Q000378:metabolism* / Q000502:physiology*; D009195:Peroxidase / Q000378:metabolism; D010650:Phenylalanine Ammonia-Lyase / Q000378:metabolism; D010829:Physiological Phenomena / Q000502:physiology; D018520:Plant Shoots / Q000378:metabolism* / Q000502:physiology*; D011134:Polysaccharides; D013026:Space Flight / Q000379:methods; D014893:Weightlessness
chemical_list: D003373:Coumaric Acids; D011134:Polysaccharides; C516502:diferulic acid; D008031:Lignin; C004999:ferulic acid; D009195:Peroxidase; D010650:Phenylalanine Ammonia-Lyase