Abstract:Desiccation is the main abiotic stress for Pyropia yezoensis. In this study we investigated the photosynthetic and antioxidant physiological responses of a wild P. yezoensis thallus to desiccation stress, including the optimal chlorophyll fluorescence quantum yields of photosystem Ⅱ (Fv/Fm), the contents of photosynthetic pigments [chlorophyll a (Chl a), carotenoid (Car), R-phycoerythrin (R-PE), R-phycocyanin (R-PC)], soluble proteins (SPs), malondialdehyde (MDA), and the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT). The results revealed that as the water loss increased, Fv/Fm decreased linearly and reached the lowest when the water loss was 60%; Fv/Fm returned to the normal level after the blades were rehydrated for 1 h. The contents of Chl a, Car, and SPs decreased gradually. The contents of R-PE and R-PC decreased when the water loss was <30% and then increased as the water loss was ≥30%. The change of phycobiliproteins/soluble proteins was similar to that of phycobiliproteins. This ratio increased to the control level when the water loss was 40% and was significantly higher than the control when the water loss was 80%. There was no significant difference in the content of MDA between the control and the blades when the water loss was ≤30%. The content of MDA increased significantly when the water loss was ≥40%. However, there was no significant difference between the blades when the water loss ranged from 40% to 80%. There was no significant change in the activities of SOD and CAT when the water loss was ≤20%. The activity of POD was significantly increased when the water loss was ≤20%. When the water loss increased to 30%, the activities of SOD, CAT and POD decreased significantly. There was no significant difference between the blades when the water loss ranged from 50% to 80%. The results above suggested that during the early stage of water loss, the antioxidant enzymes POD, CAT and SOD played key roles in scavenging the reactive oxygen species, which inhibited the yield of excessive MDA; as water loss increased, the water condition became disadvantageous for the antioxidant enzymes, and MDA was accumulated as a result. Based on the change of phycolibiprotein/SP, we speculated that the function of phycobiliproteins became more and more significant in protecting the blades against desiccation stress when the water loss was ≥30%, which could help with the rapid recovery of photosynthesis (Fv/Fm) during rehydration.
