Light-dependent Changes in Chlorophyll Fluorescence from Thalli of Porphyra tenera under Osmotic Dehydration and Subsequent Rehydration are not Related with Water Flux

Algae > Volume 13(2); 1998 > Article

Algae 1998;13(2): 241-249.

Tae-Hoon Kim, Dang-Diem Hong, Mi-Sook Hwang, Ik-Kyo Chung, Choon-Hwan Lee

Department of Molecular Biology, Pusan National University, National Center for Natural Science and Technology, Institute of Biotechnology, Namhae Hatchery, South Sea Fisheries Research Institute, National Fisheries Research and Development Institute, Department of Marine Science, Pusan National University

ABSTRACT

In red alga, Porphyra tenera, photochemical efficiency or Fv/Fm decreased in a biphasic manner in thalli treated with 9% or 12% NaCl, with a rapid phase observed within 10min and followed by a slow phase. During rehydration, the increasing pattern of Fv/Fm was also biphasic. The changes in Fv/Fm was mainly due to the changes in a background fluorescence, Fo, and more pronounced changes in these parameters were observed in the light than in darkness. The increase of Fo during osmotic dehydration was not due to the hindrance of excitation energy transfer from phycobilisome to photosystem (PS)II. Instead, the fluorescence emission from PSII decreased without significant changes in PSI fluorescence. Water fluxes in and out of Porphyra thalli were monitored by the changes in cell volume using a light microscope or indirectly by the changes in absorbance at 750nm. The rapid water efflux was completed within 4min, and the rapid influx within 1-2min. The kinetics of the water flux was different from that of the Fo change, and the water flux was independent of the presence of light. These results suggest that the lightdependent changes in Fo are not directly related with the rapid changes in the water flux. The possible candidates for the adaptation mechanism are discussed.

Key words: cell volume, chlorophyll fluorescence, low temperature fluorescence spectra, Porphyra, salinity, water flux