Effect of a cationic cellulosic polymer on gametophytes of Laminaria digitata (Laminariaceae, Phaeophyta): Improvement of dispersed 'free-living' cultures

As filament aggregation is responsible for heterogeneity of Laminariales ga metophyte cultures, a project was conducted to obtain stable homogeneous 'f ree-living' cultures of Laminaria digitata gametophytes. The alga was culti vated at 15 degrees C under low light and in the presence of a cationic cel lulosic polymer, JR125. With 0.1% polymer in the culture medium, the filame nts were dispersed and did not adhere to the culture vessel. The absence of any effect of the closely related, but uncharged, polymer LR-250 Natrasol on filament aggregation indicated that the cationic nature of the JR125 mol ecule was involved in gametophyte dissociation. In the presence of JR125, t he gametophytes showed active vegetative growth; the doubling time, measure d as chlorophyll concentration, was 5 days. The outer surface of the cell w all was clearly modified by the polymer treatment, as observed by transmiss ion electron microscopy, while neither the inner cell wall or cell organell es were affected. Physiological studies indicated that JR125 treatment did not disturb cell physiology, there being no effect on respiration, photosyn thetic activity, sensitivity to high-light stress or modification of pigmen t or fluorescence characteristics. We have therefore established the condit ions for maintaining a stable culture of mixed male and female Laminaria di gitata gametophytes in active vegetative growth. The presence of JR 125 in the medium yields a homogeneous culture without cell physiology becoming mo dified.