Effects of culture temperature on growth, maturation, conchospore developmental patterns and sex type for the boreal species Pyropia ezokurogii (Bangiales, Rhodophyta)

The boreal red alga Pyropia ezokurogii has a unique monoicous nature in which the male and female portions are separated by a vertical boundary. To determine the most favourable temperature within the tested range for the species under laboratory conditions, we compared the growth and maturation of ‘conchocelis’ and gametophytic blades cultured under four temperature conditions (5, 10, 15 and 20°C). The results indicated that the most favourable temperature within the tested range for the growth and maturation of conchocelis was 20°C. In gametophytic blades, the most favourable temperature within the tested range for growth was 10°C, whereas for maturation it was 20°C. Furthermore, we investigated the effects of temperature conditions on bilateral cell division during early conchospore germination and on sex type in gametophytic blades. Conchospore germlings exhibited bilateral cell division when the longitudinal cell number was between two and three. All gametophytic blades examined were monoicous, with male and female portions separated by a vertical boundary. These results demonstrate that bilateral cell division during early conchospore germination and sex type in P. ezokurogii are stable across different temperatures. Based on these results, P. ezokurogii has the potential to serve as a model organism for studies on sex determination and sexual differentiation in Pyropia.