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Suppression of Hydroxycinnamate Network Formation in Cell Walls of Rice Shoots Grown under Microgravity Conditions in Space.

Wakabayashi K, Soga K, Hoson T, Kotake T, Yamazaki T, Higashibata A, Ishioka N, Shimazu T, Fukui K, Osada I, Kasahara H, Kamada M - PLoS ONE (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka, Japan.

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.

No MeSH data available.


Related in: MedlinePlus

Amounts of DFA isomers in the cell walls of rice shoots.DFA isomers were analyzed by HPLC on a reversed-phase column. The figure shows means ± SE from three independent samples. *Mean values significantly different between artificial (on-orbit) 1 g and microgravity conditions (Student's t-test, P < 0.05).
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pone.0137992.g003: Amounts of DFA isomers in the cell walls of rice shoots.DFA isomers were analyzed by HPLC on a reversed-phase column. The figure shows means ± SE from three independent samples. *Mean values significantly different between artificial (on-orbit) 1 g and microgravity conditions (Student's t-test, P < 0.05).

Mentions: Our previous study showed that the cell walls of etiolated (dark-grown) rice shoots contained three major DFA isomers: 5–5, 8-O-4, and 8–5 (8–5 benzofuran) forms [20]. A similar distribution of DFA isomers has been observed in the cell walls of wheat shoots [37, 38]. The amounts per shoot of these three DFA isomers increased substantially from 4 d to 5.3 d (Fig 3), as did FA content (Fig 2). The amount of DFA isomers in microgravity-grown shoots was significantly lower than in 1 g-grown shoots on 5.3 d, while the amounts were almost the same in shoots from both conditions on 4 d (Fig 3). This indicates that a microgravity environment reduced DFA formation, that is the coupling of FA residues, in shoot cell walls. While gravitational conditions did not affect the amount of cell wall polysaccharides (Table 2), the concentration of DFA in cell walls was lower in microgravity-grown shoots than in 1 g-grown shoots. In cell walls of gramineous shoots, the decrease in the amount of DFA contributes in maintaining the cell wall extensible or loosened [12, 14, 15, 39]. Therefore, decreased ferulate network formation probably contributes to keeping the cell wall loose under microgravity conditions. In contrast, hypergravity treatment increased DFA content in cell walls of wheat shoots [23].


Suppression of Hydroxycinnamate Network Formation in Cell Walls of Rice Shoots Grown under Microgravity Conditions in Space.

Wakabayashi K, Soga K, Hoson T, Kotake T, Yamazaki T, Higashibata A, Ishioka N, Shimazu T, Fukui K, Osada I, Kasahara H, Kamada M - PLoS ONE (2015)

Amounts of DFA isomers in the cell walls of rice shoots.DFA isomers were analyzed by HPLC on a reversed-phase column. The figure shows means ± SE from three independent samples. *Mean values significantly different between artificial (on-orbit) 1 g and microgravity conditions (Student's t-test, P < 0.05).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4574559&req=5

pone.0137992.g003: Amounts of DFA isomers in the cell walls of rice shoots.DFA isomers were analyzed by HPLC on a reversed-phase column. The figure shows means ± SE from three independent samples. *Mean values significantly different between artificial (on-orbit) 1 g and microgravity conditions (Student's t-test, P < 0.05).
Mentions: Our previous study showed that the cell walls of etiolated (dark-grown) rice shoots contained three major DFA isomers: 5–5, 8-O-4, and 8–5 (8–5 benzofuran) forms [20]. A similar distribution of DFA isomers has been observed in the cell walls of wheat shoots [37, 38]. The amounts per shoot of these three DFA isomers increased substantially from 4 d to 5.3 d (Fig 3), as did FA content (Fig 2). The amount of DFA isomers in microgravity-grown shoots was significantly lower than in 1 g-grown shoots on 5.3 d, while the amounts were almost the same in shoots from both conditions on 4 d (Fig 3). This indicates that a microgravity environment reduced DFA formation, that is the coupling of FA residues, in shoot cell walls. While gravitational conditions did not affect the amount of cell wall polysaccharides (Table 2), the concentration of DFA in cell walls was lower in microgravity-grown shoots than in 1 g-grown shoots. In cell walls of gramineous shoots, the decrease in the amount of DFA contributes in maintaining the cell wall extensible or loosened [12, 14, 15, 39]. Therefore, decreased ferulate network formation probably contributes to keeping the cell wall loose under microgravity conditions. In contrast, hypergravity treatment increased DFA content in cell walls of wheat shoots [23].

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Graduate School of Science, Osaka City University, Sumiyoshi-ku, Osaka, Japan.

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.

No MeSH data available.


Related in: MedlinePlus