Relationship between the Deposition of Phenolic Acids in the Cell Walls and the Cessation of Rapid Growth in Internodes of Floating Rice

We examined the involvement of p-coumaric, ferulic and 5-5-coupled diferulic acids ester-linked to cell walls in determining the elongation rate of internodes of floating rice (Oryza saliva L.). When floating rice stem segments were exposed to air after 2 days of submergence, the elongation rate of internodes was reduced and the degree of reduction was greater in the light than in the dark, while the internodes of stem segments submerged further for a comparable period continued rapid elongation. The amounts of ferulic and 5-5-coupled diferulic acids in the cell walls in the elongation zone of internodes significantly increased during the first day after exposure to air either in light or darkness. The increase of these phenolics in the cell walls after exposure to air was also observed on the second day in light, but not in darkness. On the other hand, the amount of p-coumaric acid increased only slightly on the first day after exposure to air, but rapidly on the second day in light. This pattern of change in the amounts of p-coumaric acid resembled that in the cell-wall mass (dry weight). The application of sucrose to the segments in darkness increased the amounts of phenolics in the cell walls of internodes to almost the same amount as those in light. These results indicate that the accumulation of ferulic and 5-5-coupled diferulic acids in cell walls may be related to the cessation of internodal elongation in floating rice and that the synthesis of phenolics in the cell wall is caused partially by the provision of sugar in light.