Algae. 2001; 16(2): 151-155.

Differences in Photosynthesis and Nucleic Acid Content between Sterile and Fertile Parts of the Sporophyte of Laminaria japonica (Phaeophyceae)

Kazumi Nimura, Hiroyuki Mizuta

Laboratory of Breeding Biology, Graduate School of Fisheries Science, Hokkaido University

We investigated the differences in photosynthesis and nucleic acid contents between sterile and fertile parts of sporphyte of Laminaria japonica Areschoug using naturally collected plants and cultured discs obtained from them. The photosynthetic activity of the natural sporophyte was lower in the fertile parts than in the sterile parts, but the respiratory rates in the fertile parts were higher than in the sterile parts. Low photosynthesis and high respiratory rates were observed in the cultured discs from the sporophytes. The fertile parts of natural sporophytes and cultured discs had a high RNA/DNA ratio, indicating the activation of protein synthesis. The DNA content increased with production of zoospores and chloroplasts in the zoosporangia. Physiological changes in sorus development were the same as for naturally collected sporophytes and cultured discs. These results suggest that disc culturing is a useful method for the physiological study of reproduction of Laminaria sporophytes.

Keywords : brown algae, Laminaria japonica, nucleic acid, photosynthesis, sorus