Tolerance to oxidative stress induced by desiccation in Porphyra columbina (Bangiales, Rhodophyta).

Unravelling the mechanisms underlying desiccation tolerance is crucial in order to understand the position of algal species in the intertidal zone. The alga Porphyra columbina lives in the uppermost part of the rocky intertidal zones around the world and was selected as a model for this study. Naturally desiccated plants were collected during low tide and studied for morphological changes, oxidative burst induction, biomolecule oxidation, antioxidant responses, and photosynthetic status. Naturally hydrated plants collected during high tides were used for comparative purposes. In addition, changes induced by desiccation were assessed in vitro and the capacity to recover from desiccation was determined by rehydrating the fronds in seawater. The global results show that desiccation induces morphological and cellular alterations accompanied by a loss of ∼96% of the water content. Overproduction of reactive oxygen species (ROS) was induced by desiccation and two peaks of H(2)O(2) were detected at 1 and 3 h of desiccation. However, during in vitro rehydration post-desiccation, the ROS quickly returned to the basal levels. At the biomolecular level, only a low production of oxidized proteins was recorded during desiccation, whereas the activity of diverse antioxidant enzymes increased. However, this activity diminished to near basal levels during rehydration. The photosynthetic efficiency (F(v)/F(m)) during desiccation declined by 94-96% of the values recorded in hydrated plants. This reduction was generated by the low levels of trapped energy flux per cross-section (TRo/CS), electron transport flux per CS (ETo/CS), and density of reaction centres (RC/SCo) as well as the chlorophyll content. The inverse pattern was observed for the levels of phycocyanin and phycoerythrin content. F(v)/F(m) and the photosynthetic indicators were restored to normal levels after only 5 min of rehydration. The results indicate that desiccation in P. columbina causes overproduction of ROS that is efficiently attenuated. The morphological and photosynthetic changes could be operating as tolerance mechanisms due to the fact that these responses principally prevent biomolecular alteration and cellular collapse. Thus, the activation of different physiological mechanisms helps to explain the high tolerance to desiccation of P. columbina and, at least in part, the position of this species at the highest level in the intertidal zone.

Visualization of nuclear localization of transcription factors with cyan and green fluorescent proteins in the red alga Porphyra yezoensis.

Transcription factors play a central role in expression of genomic information in all organisms. The objective of our study is to analyze the function of transcription factors in red algae. One way to analyze transcription factors in eukaryotic cells is to study their nuclear localization, as reported for land plants and green algae using fluorescent proteins. There is, however, no report documenting subcellular localization of transcription factors from red algae. In the present study, using the marine red alga Porphyra yezoensis, we confirmed for the first time successful expression of humanized fluorescent proteins (ZsGFP and ZsYFP) from a reef coral Zoanthus sp. and land plant-adapted sGFP(S65T) in gametophytic cells comparable to expression of AmCFP. Following molecular cloning and characterization of transcription factors DP-E2F-like 1 (PyDEL1), transcription elongation factor 1 (PyElf1) and multiprotein bridging factor 1 (PyMBF1), we then demonstrated that ZsGFP and AmCFP can be used to visualize nuclear localization of PyElf1 and PyMBF1. This is the first report to perform visualization of subcellular localization of transcription factors as genome-encoded proteins in red algae.