The real-time measurements of PSII photochemical efficiency in the microscopic sporophyte of Pyropia yezoensis f. narawaensis (Bangiaceae) reveals the low capacity of desiccation tolerance that drops within a few minutes of dehydration

Abstract

The photochemical efficiency of photosystem II under desiccation stress was examined in the microscopic sporophyte of a cultivated red alga, Pyropia yezoensis f. narawaensis (= Neopyropia yezoensis f. narawaensis; Bangiales) from Saga, Japan, using a pulse amplitude modulation (PAM)-chlorophyll fluorometer. The effective quantum yield (ΔF/Fm') of sporophytes on dead oyster shells was measured every 20 s during the experiments. Experiments were designed to examine 0-, 1-, 2-, 3-, 5-, 7-, 10-, and 15-min of desiccation (50 % humidity) with subsequent 15-min rehydration in seawater at 24 °C under dim light (2 μmol photons m−2 s−1). The results showed that the ΔF/Fm' quickly dropped to zero or almost zero under 5-, 7-, 10-, and 15-min desiccation treatments with no recovery during the subsequent 15-minute rehydration period. However, in sporophytes of the 1-, 2-, and 3-minute desiccation treatments, the ΔF/Fm' declined but did not drop to zero; the ΔF/Fm' gradually recovered during the subsequent 15-minute rehydration period. An additional experiment was conducted under 3- and 5-minute desiccation treatments at four different levels of irradiance (2, 20, 100, 500 μmol photons m−2 s−1), which revealed that an increase in irradiance enhances the effects of desiccation. It appears that the photochemical efficiency of microscopic sporophytes is sensitive to desiccation, whereas the macroscopic gametophyte is more tolerant to desiccation. We recommend that during conchospore seeding of Nori-net cultivation, the effects of desiccation should be minimized to ensure stable production.