Factors of regulating internode elongation during sprouting of tubers in Sagittaria trifolia and S. pygmaea

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Internode elongation of Sagittaria trifolia plants was induced by submergence irrespective of cover soil or glass beads.On the other hand, submergence-induced internode elongation of S. pygmaea plants was dependent on the presence of cover soil or glass beads. We examined gaseous factors responsible for the enhanced internode elongation in these species, because gas accumulation easily occurs in submerged plant tissues. Treatment of the plant hormone ethylene, which is known to enhance elongation growth in many aquatic plant species, indeed stimulated leaf elongation but failed to promote internode elongation in both Sagittaria species. We found that hypoxia or anoxia generated by submergence serves as an initial growth-promoting factor for internode elongation in S. trifolia, and carbon dioxide accumulated during submergence trigger internode elongation in S. pygmaea.