Changes in expansin activity and cell wall susceptibility to expansin action during cessation of internodal elongation in floating rice |
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Authors: | Daisuke Sasayama Tetsushi Azuma Kazuyuki Itoh |
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Institution: | (1) Graduate School of Agricultural Science, Kobe University, Kobe 657-8501, Japan |
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Abstract: | We investigated the involvement of expansin action in determining the growth rate of internodes of floating rice (Oryza sativa L.). Floating rice stem segments in which rapid internodal elongation had been induced by submergence for 2 days were exposed
to air or kept in submergence for 2 more days. Both treatments reduced the elongation rate of the internodes, and the degree
of reduction was much greater in air-exposed stem segments than in continually submerged segments. These rates of internodal
elongation were correlated with acid-induced cell wall extensibility and cell wall susceptibility to expansins in the cell
elongation zone of the internodes, but not with extractable expansin activity. These results suggest that the reduced growth
rate of internodes must be due, at least in part, to the decrease in acid-induced cell wall extensibility, which can be modulated
through changes in the cell wall susceptibility to expansins rather than through expansin activity. Analysis of the cell wall
composition of the internodes showed that the cellulosic and noncellulosic polysaccharide contents increased in response to
exposure to air, but they remained almost constant under continued submergence although the cell wall susceptibility to expansins
gradually declined even under continued submergence. The content of xylose in noncellulosic neutral sugars in the cell walls
of internodes was closely and negatively correlated with changes in the susceptibility of the walls to expansins. These results
suggest that the deposition of xylose-rich polysaccharides into the cell walls may be related to a decrease in acid-induced
cell wall extensibility in floating rice internodes through the modulation of cell wall susceptibility to expansins. |
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Keywords: | Cell wall Deepwater rice Expansin Floating rice Internode elongation Submergence |
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