Photosynthetic response of a cultivated red alga, Neopyropia yezoensis f. narawaensis (=Pyropia yezoensis f. narawaensis; Bangiales, Rhodophyta) to dehydration stress differs with between two heteromorphic life-history stages

Abstract The chronic effect of dehydration on photochemical efficiency was determined in two heteromorphic life-history stages of a cultivated red alga, Neopyropia yezoensis f. narawaensis (=Pyropia yezoensis f. narawaensis; Bangiaceae, Bangiales) from Saga, Kyushu Island, Japan. The response to acute emersion (~1440-min) under 50% humidity was dissimilar between the two life-history stages, and the effective quantum yields of photosystem II of the microscopic sporophyte dropped to zero after a 5-min of emersion. The effective quantum yields did not recover to initial values, regardless of a subsequent 24 h immersion in seawater. In contrast, those of the macroscopic gametophyte almost returned to initial values after the subsequent 24 h immersion in seawater. However, when the two life-history stages were under 99% humidity, effective quantum yields did not drop after 504-h (21 days) of emersion, suggesting that the thallus was never truly dehydrated due to 99% humidity. Furthermore, effective quantum yields fell when the absolute water content of the sporophyte in the dead oyster shells dropped below the absolute water content of 90% under the 50% humidity condition, and it did not recover to initial values even after a subsequent 24-h immersion in seawater. In contrast, effective quantum yields of the gametophyte decreased when the absolute water content was less than 60%; however, effective quantum yields quickly recovered after a subsequent 30-min immersion in seawater for individuals with the absolute water content over 10%. All absolute water content treatments, including 1%, of gametophytes eventually returned to initial values after 24-h immersion in seawater. Consequently, unlike the macroscopic gametophyte, photochemical efficiency in microscopic sporophyte appears to be sensitive to dehydration stress, suggesting that farming protocols for the conchospore seeding in Nori-net cultivation need to pay careful attention to dehydration to ensure a successful production.