Effects of Different Short-Term UV-B Radiation Intensities on Metabolic Characteristics of Porphyra haitanensis.

The effects of ultraviolet (UV) radiation, particularly UV-B on algae, have become an important issue as human-caused depletion of the protecting ozone layer has been reported. In this study, the effects of different short-term UV-B radiation on the growth, physiology, and metabolism of Porphyra haitanensis were examined. The growth of P. haitanensis decreased, and the bleaching phenomenon occurred in the thalli. The contents of total amino acids, soluble sugar, total protein, and mycosporine-like amino acids (MAAs) increased under different UV-B radiation intensities. The metabolic profiles of P. haitanensis differed between the control and UV-B radiation-treated groups. Most of the differential metabolites in P. haitanensis were significantly upregulated under UV-B exposure. Short-term enhanced UV-B irradiation significantly affected amino acid metabolism, carbohydrate metabolism, glutathione metabolism, and phenylpropane biosynthesis. The contents of phenylalanine, tyrosine, threonine, and serine were increased, suggesting that amino acid metabolism can promote the synthesis of UV-absorbing substances (such as phenols and MAAs) by providing precursor substances. The contents of sucrose, D-glucose-6-phosphate, and beta-D-fructose-6-phosphate were increased, suggesting that carbohydrate metabolism contributes to maintain energy supply for metabolic activity in response to UV-B exposure. Meanwhile, dehydroascorbic acid (DHA) was also significantly upregulated, denoting effective activation of the antioxidant system. To some extent, these results provide metabolic insights into the adaptive response mechanism of P. haitanensis to short-term enhanced UV-B radiation.

Bioremediation efficiency of the largest scale artificial Porphyra yezoensis cultivation in the open sea in China.

The bioremediation efficiency of China's largest scale Porphyra yezoensis cultivation for removing dissolved nutrients and controlling harmful algae was studied in the radial sandbanks waters of Jiangsu Province in the year 2012-2013. Mean nutrient concentration values in the P. yezoensis cultivation area were significantly lower than those in the non-cultivation area, especially during the cultivation season (p<0.05). Tissue nitrogen and phosphorus contents of seaweeds were 5.99-0.80% (dry weight (DW)) and 0.16-0.19% (DW), respectively. Production of P. yezoensis was 58950.87tons DW. Based on these values, 3688.15tons of tissue nitrogen and 105.61tons of tissue phosphorus were removed by harvesting P. yezoensis. The richness index of the red tide species Skeleton emacostatum declined from 0.32 to 0.05 during the P. yezoensis cultivation season. These results indicate that large-scale cultivation of P. yezoensis can be used to efficiently alleviate eutrophication and control harmful algae blooms in open sea.

The physiological links of the increased photosystem II activity in moderately desiccated Porphyra haitanensis (Bangiales, Rhodophyta) to the cyclic electron flow during desiccation and re-hydration.

Photosynthetic electron flow changed considerably during desiccation and re-hydration of the intertidal macroalgae Porphyra haitanensis. Activities of both photosystem (PSI) and photosystem (PSII) increased significantly at moderate desiccation levels. Whereas PSII activity was abolished at an absolute water content (AWC) <24 %, PSI remained active with progressive decreases in AWC to values as low as 16 %. This result suggested that cyclic electron flow around PSI was still active after inactivation of linear electron flow following severe desiccation. Moreover, the PSI activity was restored more rapidly than that of PSII upon re-hydration. Pretreatment of the blades with 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU) suppressed PSII activity following desiccation to an AWC of ~16 % AWC. Cyclic electron flow around PSI decreased markedly in blades pretreated with DCMU than in blades without pretreatment of DCMU during re-hydration in seawater containing DCMU. All results suggested that the activity of PSII under desiccation conditions plays an important role in the operation of cyclic electron flow during desiccation and its recovery during re-hydration. Therefore, we proposed the PSII activity during desiccation could eventually lead to the accumulation of NADPH, which could serve as electron donor for P700(+) and promote its recovery during re-hydration, thereby favoring the operation of cyclic electron flow.

Variation of expression levels of seven housekeeping genes at different life-history stages in Porphyra yezoensis.

In order to identify the optimal internal control for relative real-time PCR when studying target gene expression in the red alga Porphyra yezoensis, we quantified the expression of seven housekeeping genes (18S ribosomal RNA, 30S ribosomal protein S8, Polyubiquitin-2, Glyceraldehyde-3-phosphate dehydrogenase, Elongation factor 1-alpha, Beta-tubulin and Actin 3) at different life-history stages. Absolute quantification was done by normalization to total RNA quantity and by normalization to genomic DNA quantity. We used these two normalization approaches, comparing the differences of expression levels of all candidate housekeeping genes between any two generations and across three life-history stages (filamentous sporophytes, leafy gametophytes and conchospores). We found GAPDH had the best stability in all cases and we recommend that GAPDH be considered as a potential internal control for gene expression studies at different life-history stages in P. yezoensis.

Molecular identification of green algae from the rafts based infrastructure of Porphyra yezoensis.

To provide more information on the origin of the Ulva prolifera bloom in Qingdao sea area in China from 2007 to 2011, the diversity of green algae growing on the rafts of Porphyra yezoensis on the coast in Jiangsu Province was investigated based on ITS, rbcL and 5S sequences. Eighty-four of green algal samples from various sites and cruises in 2010 and 2011 were collected. According to ITS and rbcL sequences, samples from the rafts of P. yezoensis fell into four clades: Ulva linza-procera-prolifera (LPP) complex, Ulva flexuosa, Blidingia sp. and Urospora spp. However, based on the 5S rDNA, a more resolved DNA marker, only one of the 84 samples belonged to U. prolifera. Combined with the previous reports, it is likely that U. prolifera bloom in Qingdao sea area might consist of more than one origin, and Porphyra cultivation rafts might be one of the causes.

The enhancement of cyclic electron flow around photosystem I improves the recovery of severely desiccated Porphyra yezoensis (Bangiales, Rhodophyta).

Porphyra yezoensis, a representative species of intertidal macro-algae, is able to withstand periodic desiccation at low tide but is submerged in seawater at high tide. In this study, changes in photosynthetic electron flow in P. yezoensis during desiccation and re-hydration were investigated. The results suggested that the cyclic electron flow around photosystem I (PSI) increased significantly during desiccation, continued to operate at times of severe desiccation, and showed greater tolerance to desiccation than the electron flow around PSII. In addition, PSI activity in desiccated blades recovered faster than PSII activity during re-hydration. Even though linear electron flow was suppressed by DCMU [3-(3',4'-dichlorophenyl)-1,1-dimethylurea], cyclic electron flow could still be restored. This process was insensitive to antimycin A and could be suppressed by dibromothymoquinone (DBMIB). The prolonged dark treatment of blades reduced the speed in which the cyclic electron flow around PSI recovered, suggesting that stromal reductants, including NAD(P)H, played an important role in the donation of electrons to PSI and were the main cause of the rapid recovery of cyclic electron flow in desiccated blades during re-hydration. These results suggested that cyclic electron flow in P. yezoensis played a significant physiological role during desiccation and re-hydration and may be one of the most important factors allowing P. yezoensis blades to adapt to intertidal environments.

Seaweeds early development: detrimental effects of desiccation and attenuation by algal extracts.

The effects of desiccation on the early development stages of Mazzaella laminarioides, Scytosiphon lomentaria and Lessonia nigrescens, algal species with different patterns of distribution across the intertidal zone, were examined in the laboratory. In addition, the protective effect against desiccation was evaluated using algal extracts, including those from Porphyra columbina, a macroalga tolerant to desiccation that lives in the uppermost part of the intertidal zone. Our results showed that M. laminarioides displayed the highest resistance to daily desiccation, followed by S. lomentaria, whereas L. nigrescens was the most susceptible. Spores from L. nigrescens exposed to desiccation, although being able to germinate, ceased further post-germination development. In addition, our results showed that all species exposed to extracts from desiccated P. columbina successfully completed their development and strongly suggest the occurrence of compounds with protective properties that help in attenuating the stress caused by desiccation. Finally, our results indicate that the magnitude of the effects generated by desiccation on the early algal development is related to the position of the species in the intertidal zone, and that the protective effects of P. columbina extracts reveal an exceptional metabolism of this species under desiccation stress.

Morphological and photosynthetic variations in the process of spermatia formation from vegetative cells in Porphyra yezoensis Ueda (Bangiales, Rhodophyta) and their responses to desiccation.

Porphyra yezoensis has a macroscopic foliage gametophyte phase with only a single cell layer, and is ideally suited for the study of the sexual differentiation process, from the vegetative cell to the spermatia. Firstly, we compared variations in the responses of the vegetative and male sectors to desiccation. Later, cell tracking experiments were carried out during the formation of spermatia from vegetative cells. The two sectors showed similar tolerance to desiccation, and the formation of spermatia from vegetative cells was independent of the degree of desiccation. Both light and scanning electron microscopy (SEM) observations of the differentiation process showed that the formation of spermatia could be divided into six phases: the one-cell, two-cell, four-cell, eight-cell, pre-release and spermatia phases. Photomicrographs of Fluorescent Brightener staining showed that the released spermatia had no cell walls. Photosynthetic data showed that there was a significant rise in Y(II) in the four-cell phase, indicating an increase in photosynthetic efficiency of PSII during this phase. We propose that this photosynthetic rise may be substantial and provide the increased energy needed for the formation and release of spermatia in P. yezoensis.

The mechanism of adhesion and germination in the carpospores of Porphyra spiralis var. amplifolia (Rhodophyta, Bangiales).

Spore release is the primary means of dispersion employed by red algae, and it provides insight into the elements linking the stages of their life history. In most red algae, spores are released within a sheath-like envelope of mucilage, which is responsible for their primary attachment. However, few studies have characterized the polysaccharides involved in the adhesion of seaweed spores. Therefore, in this paper, the process of spore germination and adhesion in Porphyra spiralis var. amplifolia is described, as representative of the germination pattern of the Naccaria type. Using FITC-labeled lectins, we discovered high concentrations of α-D-mannose, α-D-glucose and ß-D-galactose in the mucilage. The germ tube reacted with RCA-FITC, indicating the presence ß-D-galactose, and the rhizoidal cells showed the presence of α-D-mannose, α-D-glucose and ß-D-galactose, indicating their importance to substrate adhesion. Using light and transmission electron microscopy, we also conducted an analysis of spore ultrastructure. We found that the differentiation of a vacuole in the spore is one of the most important processes marking the initial stage of germination. Thus, as the degree of vacuolation increases, whole cell contents move towards the germ tube, which undergoes several successive divisions forming the sporophytic phase. Therefore, we can conclude that germination in Porphyra spiralis var. amplifolia is characterized by (1) the fixation of carpospores in the substrate by sugars present in the mucilage and (2) the polarization of cell contents by the processes of vacuolization and germ tube formation.

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.

Porphyra: a marine crop shaped by stress.

The marine red alga Porphyra is an important marine crop, worth ∼US$1.3 billion per year. Cultivation research now includes farm ecology, breeding, strain conservation and new net-seeding technologies. The success of cultivation is due, in part, to the high stress tolerance of Porphyra. Many species of Porphyra lose 85-95% of their cellular water during the daytime low tide, when they are also exposed to high light and temperature stress. Antioxidant and mycosporine-like amino acid activities have been partially characterized in Porphyra, but, as we discuss here, the Porphyra umbilicalis genome project will further elucidate proteins associated with stress tolerance. Furthermore, phylogenomic and transcriptomic investigations of Porphyra sensu lato could elucidate tradeoffs made during physiological acclimation and factors associated with life-history evolution in this ancient lineage.

Recurrence of the world's largest green-tide in 2009 in Yellow Sea, China: Porphyra yezoensis aquaculture rafts confirmed as nursery for macroalgal blooms.

In the summer of 2008, the world's largest green-tide occurred in the Yellow Sea, China. The hypothesized cause was the expansion of Porphyra yezoensis aquaculture along the Jiangsu coastline and the re-occurrence of a green-tide in 2009 was predicted. In this study, satellite and field images showed the formation of the June 2009 green-tide which again originated from the Jiangsu coast. The responsible species, its source and biomass accumulation were studied to support the previous hypothesis. Morphological and phylogenetic analysis demonstrated the homology of Ulva prolifera in the 2008 green-tide with the U. prolifera from P. yezoensis aquaculture rafts. About 91-505kg/ha of U. prolifera was attached to the P. yezoensis aquaculture rafts and a total biomass of 4956 tonnes was estimated during the harvesting of P. yezoensis. This is sufficient to seed a bloom when they are dislodged from the rafts as a result of harvesting practices.

Photosynthetic parameters of sexually different parts of Porphyra katadai var. hemiphylla (Bangiales, Rhodophyta) during dehydration and re-hydration.

Physiological data from extreme habitat organisms during stresses are vital information for comprehending their survival. The intertidal seaweeds are exposed to a combination of environmental stresses, the most influential one being regular dehydration and re-hydration. Porphyra katadai var. hemiphylla is a unique intertidal macroalga species with two longitudinally separated, color distinct, sexually different parts. In this study, the photosynthetic performance of both PSI and PSII of the two sexually different parts of P. katadai thalli during dehydration and re-hydration was investigated. Under low-grade dehydration the variation of photosystems of male and female parts of P. katadai were similar. However, after the absolute water content reached 42%, the PSI of the female parts was nearly shut down while that of the male parts still coordinated well and worked properly with PSII. Furthermore, after re-hydration with a better conditioned PSI, the dehydrated male parts were able to restore photosynthesis within 1 h, while the female parts did not. It is concluded that in P. katadai the susceptibility of photosynthesis to dehydration depends on the accommodative ability of PSI. The relatively lower content of phycobiliprotein in male parts may be the cause for a stronger PSI after severe dehydration.

Phosphatidylinositol 3-kinase activity and asymmetrical accumulation of F-actin are necessary for establishment of cell polarity in the early development of monospores from the marine red alga Porphyra yezoensis.

The polarized distribution of F-actin is important in providing the driving force for directional migration in mammalian leukocytes and Dictyostelium cells, in which compartmentation of phosphatidylinositol 3-kinase (PI3K) and phosphatidylinositol phosphatase is critical for the establishment of cell polarity. Since monospores from the red alga Porphyra yezoensis are a real example of migrating plant cells, the involvement of the cytoskeleton and PI3K was investigated during their early development. Our results indicate that the asymmetrical localization of F-actin at the leading edge is fixed by the establishment of the anterior-posterior axis in migrating monospores, which is PI3K-dependent and protein synthesis-independent. After migration, monospores adhere to the substratum and then become upright, developing into multicellular thalli via the establishment of the apical-basal axis. In this process, F-actin usually accumulates at the bottom of the basal cell and development after migration requires new protein synthesis. These findings suggest that the establishment of anterior-posterior and apical-basal axes are differentially regulated during the early development of monospores. Our results also indicate that PI3K-dependent F-actin asymmetry is evolutionally conserved in relation to the establishment of cell polarity in migrating eukaryotic cells.

Taxonomy, molecular phylogeny, and ultrastructural morphology of Olpidiopsis porphyrae sp. nov. (Oomycetes, straminipiles), a unicellular obligate endoparasite of Bangia and Porphyra spp. (Bangiales, Rhodophyta).

Olpidiopsis porphyrae sp. nov., a marine oomycete endoparasite that infects the commercially cultivated red alga Porphyra yezoensis, is described and its phylogenetic position based on molecular data and ultrastructural morphology is discussed. O. porphyrae infects the host Porphyra by means of encysted zoospores. Spherical-shaped holocarpic thalli develop within the cytoplasm of its algal host, which produce monoplanetic, subapically biflagellate zoospores. The characteristic features of this isolate are the ellipsoidal, unicellular thallus and simple holocarpic zoosporangial development, which show morphological similarity with the genus Olpidiopsis. Laboratory infection experiments with a wide range of green, brown, and red algae revealed that O. porphyrae infects several stages of the bangialean red algae (the genera Bangia and Porphyra). Molecular phylogenetic analyses inferred from both SSU rRNA and cox2 genes showed O. porphyrae branched before the main saprolegnian and peronosporalean lineages within the monophyletic oomycete clade, indicating its phylogenetic separation from them. A single or double K-body-like organelle, which contains tubular inclusions, is found located to one side of the zoospore nucleus and shows similarities to homologous organelles previously described in O. saprolegniae. The ultrastructural morphology of O. porphyrae with zoospore initials containing K-bodies and tubular mitochondrial cristae is characteristic of oomycetes. Group I intron-like multiple insertions were found in the SSU rRNA gene of O. porphyrae. This is the first report of SSU group I introns in the class Oomycetes.

Effect of light quality on the accumulation of photosynthetic pigments, proteins and mycosporine-like amino acids in the red alga Porphyra leucosticta (Bangiales, Rhodophyta).

The effect of different light qualities (white, blue, green, yellow and red light) on photosynthesis, measured as chlorophyll fluorescence, and the accumulation of photosynthetic pigments, proteins and the UV-absorbing mycosporine-like amino acids (MAAs) was studied in the red alga Porphyra leucosticta. Blue light promoted the highest accumulation of nitrogen metabolism derived compounds i.e., MAAs, phycoerythrin and proteins in previously N-starved algae after seven days culture in ammonium enriched medium. Similar results were observed in the culture under white light. In contrast, the lowest photosynthetic capacity i.e., lowest electron transport rate and lowest photosynthetic efficiency as well as the growth rate were found under blue light, while higher values were found in red and white lights. Blue light favored the accumulation of the MAAs porphyra-334, palythine and asterina-330 in P. leucosticta. However, white, green, yellow and red lights favored the accumulation of shinorine. The increase of porphyra-334, palythine and asterina-330 occurred in blue light simultaneous to a decrease in shinorine. The accumulation of MAAs and other nitrogenous compounds in P. leucosticta under blue light could not be attributed to photosynthesis and the action of a non-photosynthetic blue light photoreceptor is suggested. A non-photosynthetic photoreceptor could be also involved in the MAAs interconversion pathways in P. leucosticta.