Evaluation of salinity effects on the release, adhesion, and germination of the tetraspores of Gelidium floridanum (Rhodophyta, Florideophyceae)

Abstract

The release, adhesion, and germination of tetraspores determine the successful development of the red seaweed Gelidium floridanum. The aim of this study was to investigate the effects of salinity on the initial development of G. floridanum tetraspores. To accomplish this, tetraspores were released and allowed to germinate under salinity of 24, 28, 32, 36, and 40 psu for a period of 6 to 24 h. Samples were processed for light, confocal, and transmission electron microscopy to analyze the ultrastructural characteristics, as well as analyses of the cell viability (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT)) and quantification of photosynthetic pigments. At 32 psu, tetraspores exhibited normal characteristics with germ tube formation after 6 h and rhizoid formation after 24 h. Under hyposalinity of 24 psu, tetraspores did not form a germ tube after 6 h, and no development at all occurred after 24 h. Thus, the development of tetraspores was inhibited, resulting in nonviable cells or disorganized cytoplasmic contents. Tetraspores cultivated in hypersaline conditions (40 psu) showed a delay in development. After only 6 h of culture, samples in both hyposaline and hypersaline conditions showed differences in photosynthetic pigments, and such pigments tend to stabilize after 24 h. Based on these results, we can conclude that this species has only limited tolerance to salinity in the range of 28 to 36 psu and that salinity above or below these values is sufficient to change the pattern of development of G. floridanum tetraspores.