Chronic effects of three different stressors, irradiance, temperature, and desiccation, on the PSII photochemical efficiency in the heteromorphic life-history stages of cultivated Pyropia yezoensis f. narawaensis (Bangiales) from Japan

The chronic effects of three different stressors, irradiance, temperature, and desiccation, on Photosystem II (PSII) photochemical efficiency were investigated in two heteromorphic life-history stages of a cultivated red alga, Pyropia yezoensis f. narawaensis (Bangiales) from Japan. The maximum quantum yields of PSII (F-v/F-m) over the range of temperature between 4 and 36 degrees C for 96-h exposure showed different responses in the two life-history stages. In the macroscopic gametophyte, the highest value (0.47) occurred at 12.0 degrees C; however, F-v/F-m quickly decreased at higher temperatures. In contrast, F-v/F-m in the microscopic sporophyte were less sensitive to temperature, suggesting adaptation to the broad range of temperature with a high value (0.40) that occurred at 21.1 degrees C. Continuous 6-h exposures to the 50, 100, and 1000 mu mol photons m(-2) s(-1) revealed greater decline in their effective quantum yields of PSII (Delta F/F-m ') in the sporophyte. As known in the photoprotective response and its PSII repair system in the photosynthesis, the recovery of quantum yield in two life-history stages after subsequent acclimation (darkness and dim-light treatments) was more accelerated in dim-light than those of darkness. The response to continuous desiccation (240-min aerial exposure) in two life-history stages was also different, and the Delta F/F-m ' in the gametophyte returned to initial values after re-immersion in seawater. In contrast, those in the sporophyte dropped to zero after a 5-min aerial exposure and did not return to initial values, suggesting that farming protocols for the conchospore seeding in Nori-net cultivation need to pay careful attention to desiccation to ensure successful production.