Desiccation tolerance and underlying mechanisms for the recovery of the photosynthetic efficiency in the tropical intertidal seagrasses Halophila ovalis and Thalassia hemprichii

Abstract

Abstract The seagrasses Halophila ovalis and Thalassia hemprichii commonly occur in the upper-intertidal zone where they are subjected to prolonged desiccation during low tides. This study investigated their desiccation tolerance and the mechanisms underlying their eventual recovery. Halophila ovalis exhibited a faster decline in photosynthetic efficiency, measured as effective quantum yield of photosystem II (φPSII), during 90 min of desiccation and did not recover when rehydrated. Thalassia hemprichii, however, showed a nearly full recovery. Desiccation also imposed greater membrane damage on H. ovalis as indicated by a higher electrolyte leakage. In a subsequent experiment, seagrasses were desiccated for 60 min before being rehydrated with seawater containing either chloramphenicol (CMP), cycloheximide (CHX), dithiothreitol (DTT) or no metabolic inhibitor (control). Recovery of φPSII of H. ovalis was hindered by CMP and DTT while CHX had little effect. Recovery of φPSII of T. hemprichii, however, was partially affected by both CMP and CHX to a similar extent and not by DTT. The results indicate that H. ovalis relies substantially on the synthesis of chloroplast-encoded proteins and excess energy dissipation by the xanthophyll cycle whereas T. hemprichii requires limited protein synthesis in both chloroplast and cytoplasm to completely recover their photosynthetic function from desiccation stress.