Effect of Iron on Oogonium Formation, Growth Rate and Pigment Synthesis of Laminaria japonica (Phaeophyta)

抄録

The effects of iron on oogonium formation of female gametophytes, growth rate and pigment syntheses of Lmninaria japonica Areschoug were investigated and compared in both soluble EDTA chelated iron (Fe (III) -EDTA) and solid amorphous hydrous ferric oxide (am-Fe (III)) media containing nitrate and phosphate. Soluble Fe (III) -EDTA [0.4-2 μM] and solid am-Fe (III) [2 μM] were found to strongly affect the oogonium formation of female gametophytes; most gametophytes in iron-free and reduced iron concentration media (<0.4 μM in Fe (III) -EDTA, <2 μM in am-Fe (III)) continued only vegetative growth without oogonium formation. The growth rate and chlorophyll-a (Chl-a) concentration of young sporophytes significantly increased with increased iron concentration in the culture media. The growth rate and Chl-a concentration of young sporophytes cultured in am-Fe (III) media were approximately one half lower than those in Fe (III) -EDTA media, possibly as a result of the lower iron uptake rate of young sporophytes observed in am-Fe (III) media. This lower iron uptake rate may be attributed to the low solubility and the slow dissolution rate reported for solid amorphous hydrous ferric oxide in seawater. Furthermore, iron was found to promote the syntheses of fucoxanthin, chlorophyll-c, β-carotene and Chl-a in adult sporophytes. This study clearly indicates that iron plays an important role in the oogonium formation, growth rate and pigment syntheses of L. japonica.