Protective function of silicon deposition in Saccharina japonica sporophytes (Phaeophyceae).

We investigated biogenic silica deposition in sporophytes of kelp, Saccharina japonica (Laminariaceae). Silicon content was measured in different sporophyte regions and there was a trend for the silicon content to increase longitudinally from the stipe-blade transition to apical regions. The transverse trend was for the content to be higher in the marginal region than in the medial region. The silicon content was also higher in the scar and sorus regions compared with the adjacent vegetative regions. High silicon content was detected in the margin of the disc and in the sorus region of cultured sporophyte discs. Moreover, rhodamine 123 staining suggested that silicon was deposited in the mouth of the marginal wound of the disc. Rhodamine 123 fluorescence was also detected in the paraphyses and mucilaginous caps of sori. These results suggest that silicon plays important roles in tissue protection and vegetative tissue wound healing. It is also suggested that silicon is required for the protection of reproductive tissues. We also discuss the physiological and ecological roles of biogenic silica deposition in kelp and its management in cultivated fields.