The Photosynthetic Mechanisms Of Membranous Algae During Asexual Propagation And Stressful Conditions

Intertidal membranous algae are important primary producers of the coast, which play a significant role in carbon cycle. The photosynthesis of these algae is a vital basis of primary productivity. Porphyra yezoensis and Ulva prolifera, representative species of intertidal zone, are economically and ecologically important species, respectively. They are chosen to study the photosynthetic properties during archeospore formation of Porphyra yezoensis and in the course of desiccation and re-hydration of Ulva prolifera basing on their biological characteristics and environmental conditions.Porphyra yezoensis is one of the most economically important marine crops. The archeospore formation, the typical biological characteristics of P. yezoensis, contributes greatly to the accumulation of the biomass of P. yezoensis in the field and is becoming a valuable seed source. The changes of cell wall and photosynthetic performance during archeospore formation are deeply studied. The results suggested that during the formation of archeospore the diameter of distal marginal cells began to gradually increase and they became golden yellow in color. The surface roughness of cells became more protuberant and rougher during archeospore formation. Ultimately, archeospore squeezed out of the torn cells. These results imply that cell walls of archeosporangia are not degraded but ruptured via swelling of the archeospore and then archeospores are discharged. In addition, the photosynthetic properties of P. yezoensis gradually increased during archeospore formation, suggesting that’energy’ is accumulated to prepare for the formation and release of archeospores.Ulva prolifera is a representative species of the intertidal macro-algae along the shores of Qingdao, China. More importantly, it is one of the causative species of the green tides that occurred along the shoreline of Qingdao in2008. We investigated the response and photochemical processes of U. prolifera to desiccation and re-hydration. The results showed that U. prolifera have a high degree of tolerance to desiccation stress. More specifically, The Y (Ⅱ) values declined sharply with desiccation, whereas the Y (Ⅰ) values increased significantly from the onset of desiccation to AWC65%caused by the high activity of PSI-driven cyclic electron flow. Moreover, the PSI-driven cyclic electron flow of U. prolifera still operated at severe levels of desiccation (22%). In addition, it is showed that the PSI activity was recovered faster than that of PSII during re-hydration of desiccated thalli.