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Species of Ulva have a wide range of commercial applications and are increasingly being recognized as promising candidates for integrated aquaculture. In South Africa, Ulva has been commercially cultivated in integrated seaweed‐abalone aquaculture farms since 2002, with more than 2000 tonnes of biomass cultivated per annum in land‐based paddle raceways. However, the identity of the species of Ulva grown on these farms remains uncertain. We therefore characterized samples of Ulva cultivated in five integrated multi‐trophic aquaculture farms (IMTA) across a wide geographical range and compared them with foliose Ulva specimens from neighboring seashores. The molecular markers employed for this study were the chloroplast‐encoded Ribulose‐1,5‐bisphosphate carboxylase oxygenase (rbcL), the Internal Transcribed Spacer (ITS) of the nuclear, and the chloroplast elongation factor tufA. All currently cultivated specimens of Ulva were molecularly resolved as a single species, U. lacinulata. The same species has been cultivated for over a decade, although a few specimens of two other species were also present in early South African IMTA systems. The name Ulva uncialis is adopted for the Ulva "Species A" by Fort et al. (2021), Molecular Ecology Resources, 22, 86) significantly extending the distribution range for this species. A comparison with wild Ulva on seashores close to the farms resulted in five new distribution records for South Africa (U. lacinulata, U. ohnoi, U. australis, U. stenophylloides, and U. aragoënsis), the first report of a foliose form of U. compressa in the region, and one new distribution record for Namibia (U. australis). This study reiterates the need for DNA confirmation, especially when identifying morphologically simple macroalgae with potential commercial applications. [ABSTRACT FROM AUTHOR]

Green seaweeds exhibit a wide range of morphologies and occupy various ecological niches, spanning from freshwater to marine and terrestrial habitats. These organisms, which predominantly belong to the class Ulvophyceae, showcase a remarkable instance of parallel evolution toward complex multicellularity and macroscopic thalli in the Viridiplantae lineage. Within the green seaweeds, several Ulva species ("sea lettuce") are model organisms for studying carbon assimilation, interactions with bacteria, life cycle progression, and morphogenesis. Ulva species are also notorious for their fast growth and capacity to dominate nutrient‐rich, anthropogenically disturbed coastal ecosystems during "green tide" blooms. From an economic perspective, Ulva has garnered increasing attention as a promising feedstock for the production of food, feed, and biobased products, also as a means of removing excess nutrients from the environment. We propose that Ulva is poised to further develop as a model in green seaweed research. In this perspective, we focus explicitly on Ulva mutabilis/compressa as a model species and highlight the molecular data and tools that are currently available or in development. We discuss several areas that will benefit from future research or where exciting new developments have been reported in other Ulva species. [ABSTRACT FROM AUTHOR]

The generalized use of molecular identification tools indicated that multispecific green tides are more common than previously thought. Temporal successions between bloom‐forming species on a seasonal basis were also revealed in different cold temperate estuaries, suggesting a key role of photoperiod and temperature controlling bloom development and composition. According to the Intergovernmental Panel on Climate Change, water temperatures are predicted to increase around 4°C by 2100 in Ireland, especially during late spring coinciding with early green tide development. Considering current and predicted temperatures, and photoperiods during bloom development, different eco‐physiological experiments were developed. These experiments indicated that the growth of Ulva lacinulata was controlled by temperature, while U. compressa was unresponsive to the photoperiod and temperatures assayed. Considering a scenario of global warming for Irish waters, an earlier development of bloom is expected in the case of U. lacinulata. This could have significant consequences for biomass balance in Irish estuaries and the maximum accumulated biomass during peak bloom. The observed seasonal patterns and experiments also indicated that U. compressa may facilitate U. lacinulata development. When both species were co‐cultivated, the culture performance showed intermediate responses to experimental treatments in comparison with monospecific cultures of both species. [ABSTRACT FROM AUTHOR]

Ulva compressa, a green tide‐forming species, can adapt to hypo‐salinity conditions, such as estuaries and brackish lakes. To understand the underlying molecular mechanisms of hypo‐salinity stress tolerance, transcriptome‐wide gene expression profiles in U. compressa were created using digital gene expression profiles. The RNA‐seq data were analyzed based on the comparison of differently expressed genes involved in specific pathways under hypo‐salinity and recovery conditions. The up‐regulation of genes in photosynthesis and glycolysis pathways may contribute to the recovery of photosynthesis and energy metabolism, which could provide sufficient energy for the tolerance under long‐term hyposaline stress. Multiple strategies, such as ion transportation and osmolytes metabolism, were performed to maintain the osmotic homeostasis. Additionally, several long noncoding RNA were differently expressed during the stress, which could play important roles in the osmotolerance. Our work will serve as an essential foundation for the understanding of the tolerance mechanism of U. compressa under the fluctuating salinity conditions. [ABSTRACT FROM AUTHOR]

To better understand the effect of temperature on the growth and nitrate reductase activity (NRA) of Ulva prolifera and their relationships, the effects of five different temperatures (10, 15, 20, 25, and 30°C) were investigated in a laboratory setup. In this study, an optimization in vitro analysis method for Ulva prolifera NRA was developed. Under different treatments, the NRA, nitrate concentration, pH, the intracellular nitrate and nitrite concentrations, and the POC/PON were evaluated. The results of the in vitro analysis method showed it was optimal for the NRA assay when the extraction time was 6 min, enzymatic reaction time 30 min, volume of phenazine methosulfate (PMS) solution 50 μL, NADH concentration 0.36 mM, and KNO3 concentration 10 mM. The maximal NRA (NRAmax) appeared on the 2nd day in the 10, 15, and 20°C (low‐temperature) groups and on the 1st day in the 25 and 30°C (high‐temperature) groups. The algal growth ended earlier at a high temperature, ending after 5 d at 30 and 25°C and 7 d at 20°C and 9 d at 15°C, and the alga at 10°C had been growing during the incubation period. Ulva prolifera cultivated in a range of 10–20°C had a long growth cycle and the NRA decreased with increasing temperature when exceeded 15°C, a positive correlation between algal growth and NRA was observed. This study supports NRA is a suitable proxy of the effects of temperature changes on the ability of Ulva prolifera to uptake and metabolize nitrogen nutrients. [ABSTRACT FROM AUTHOR]

Arabinogalactan proteins (AGPs) encompass a diverse group of plant cell wall proteoglycans, which play an essential role in plant development, signaling, plant‐microbe interactions, and many others. Although they are widely distributed throughout the plant kingdom and extensively studied, they remain largely unexplored in the lower plants, especially in seaweeds. Ulva species have high economic potential since various applications were previously described including bioremediation, biofuel production, and as a source of bioactive compounds. This article presents the first experimental confirmation of AGP‐like glycoproteins in Ulva species and provides a simple extraction protocol of Ulva lactuca AGP‐like glycoproteins, their partial characterization and unique comparison to scarcely described Solanum lycopersicum AGPs. The reactivity with primary anti‐AGP antibodies as well as Yariv reagent showed a great variety between Ulva lactuca and Solanum lycopersicum AGP‐like glycoproteins. While the amino acid analysis of the AGP‐like glycoproteins purified by the β‐d‐glucosyl Yariv reagent showed a similarity between algal and land plant AGP‐like glycoproteins, neutral saccharide analysis revealed unique glycosylation of the Ulva lactuca AGP‐like glycoproteins. Surprisingly, arabinose and galactose were not the most prevalent monosaccharides and the most outstanding was the presence of 3‐O‐methyl‐hexose, which has never been described in the AGPs. The exceptional structure of the Ulva lactuca AGP‐like glycoproteins implies a specialized adaptation to the marine environment and might bring new insight into the evolution of the plant cell wall. [ABSTRACT FROM AUTHOR]

Ulva (Ulvophyceae, Chlorophyta) is common in intertidal environments and can also be found in freshwater ecosystems. The difficulty to morphologically identify Ulva species due to cryptic diversity and morphological plasticity has caused a taxonomic conundrum. Fortunately, molecular data have begun to unravel a better understanding of its diversity. Here, we present a molecular analysis with 247 samples of Ulva from the Gulf of Mexico and Atlantic USA based on chloroplast (rbcL and tufA) and nuclear (ITS1‐5.8S‐ITS2) molecular markers. Twenty‐four Ulva taxa had previously been reported for this area based on morphology and earlier molecular studies mostly from Northeastern USA and Canada. In this study, sixteen Ulva clades were identified representing 13 named clades and putatively three undescribed species. Only nine of the 24 taxa previously reported for the Western Atlantic were confirmed. Four species were identified for the first time in the U.S. East and Gulf Coast (U. aragoënsis, U. californica, U. meridionalis, and U. tepida). This study provides a foundation for future research on Ulva in this area and reiterates the necessity of using molecular‐assisted identifications for this group. [ABSTRACT FROM AUTHOR]

Foliose Ulva spp. have become increasingly important worldwide for their environmental and financial impacts. A large number of such Ulva species have rapid reproduction and proliferation habits, which explains why they are responsible for Ulva blooms, known as "green tides", having dramatic negative effects on coastal ecosystems, but also making them attractive for aquaculture applications. Despite the increasing interest in the genus Ulva, particularly on the larger foliose species for aquaculture, their inter‐ and intra‐specific genetic diversity is still poorly described. We compared the cytoplasmic genome (chloroplast and mitochondrion) of 110 strains of large distromatic foliose Ulva from Ireland, Brittany (France), the Netherlands and Portugal. We found six different species, with high levels of inter‐specific genetic diversity, despite highly similar or overlapping morphologies. Genetic variation was as high as 82 SNPs/kb between Ulva pseudorotundata and U. laetevirens, indicating considerable genetic diversity. On the other hand, intra‐specific genetic diversity was relatively low, with only 36 variant sites (0.03 SNPs/kb) in the mitochondrial genome of the 29 Ulva rigida individuals found in this study, despite different geographical origins. The use of next‐generation sequencing allowed for the detection of a single inter‐species hybrid between two genetically closely related species, U. laetevirens, and U. rigida, among the 110 strains analyzed in this study. Altogether, this study represents an important advance in our understanding of Ulva biology and provides genetic information for genomic selection of large foliose strains in aquaculture. [ABSTRACT FROM AUTHOR]

Non‐photochemical quenching (NPQ) is an important photoprotective mechanism in plants, which dissipates excess energy and further protects the photosynthetic apparatus under high light stress. NPQ can be dissected into a number of components: qE, qZ, and qI. In general, NPQ is catalyzed by two independent mechanisms, with the faster‐activated quenching catalyzed by the monomeric light‐harvesting complex (LHCII) proteins and the slowly activated quenching catalyzed by LHCII trimers, both processes depending on zeaxanthin but to different extent. Here, we studied the NPQ of the intertidal green macroalga, Ulva prolifera, and found that the NPQ of U. prolifera lack the faster‐activated quenching, and showed much greater sensitivity to dithiothreitol (DTT) than to dicyclohexylcarbodiimide (DCCD). Further results suggested that the monomeric LHC proteins in U. prolifera included only CP29 and CP26, but lacked CP24, unlike Arabidopsis thaliana and the moss Physcomitrella patens. Moreover, the expression levels of CP26 increased significantly following exposure to high light, but the concentrations of the two important photoprotective proteins (PsbS and light‐harvesting complex stress‐related [LhcSR]) did not change upon the same conditions. Analysis of the xanthophyll cycle pigments showed that, upon exposure to high light, zeaxanthin synthesis in U. prolifera was gradual and much slower than that in P. patens, and could effectively be inhibited by DTT. Based on these results, we speculate the enhancement of CP26 and slow zeaxanthin accumulation provide an atypical NPQ, making this green macroalga well adapted to the intertidal environments. [ABSTRACT FROM AUTHOR]

The physiological and biochemical changes in the green macroalga Ulva pertusa during the progression of sporulation have been characterized. The transition from the vegetative to the sporulation stage was accompanied by an increase in chlorophyll a (Chl a), chlorophyll b (Chl b), and carotenoid content, as well as an increase in DPPH scavenging and responsiveness to diphenylamine. However, oxygen evolution and maximum electron transport rate decreased. The discrepancy between photosynthetic performance and pigment content might relate to the self‐shading of spores within a sporangium. Spore‐forming U. pertusa thalli were low‐light‐adapted, due to an increase in the number of photosynthetic units. Decreased electron transport during sporulation might trigger sporulation, as for some cyanobacteria and other Ulva spp., via oxidization of the plastoquinone pool and cyclic phosphorylation, thus producing ATP to generate carbon and nitrogen skeletons required for spores. It is thus concluded that carotenoids function both in spore initiation and/or maturation and in their photoprotection. [ABSTRACT FROM AUTHOR]

The physiological and biochemical changes in the green macroalga Ulva pertusa during the progression of sporulation have been characterized. The transition from the vegetative to the sporulation stage was accompanied by an increase in chlorophyll a (Chl a), chlorophyll b (Chl b), and carotenoid content, as well as an increase in DPPH scavenging and responsiveness to diphenylamine. However, oxygen evolution and maximum electron transport rate decreased. The discrepancy between photosynthetic performance and pigment content might relate to the self‐shading of spores within a sporangium. Spore‐forming U. pertusa thalli were low‐light‐adapted, due to an increase in the number of photosynthetic units. Decreased electron transport during sporulation might trigger sporulation, as for some cyanobacteria and other Ulva spp., via oxidization of the plastoquinone pool and cyclic phosphorylation, thus producing ATP to generate carbon and nitrogen skeletons required for spores. It is thus concluded that carotenoids function both in spore initiation and/or maturation and in their photoprotection. [ABSTRACT FROM AUTHOR]

Salt stress is a major abiotic stress factor that can induce many adverse effects on photosynthetic organisms. Plants and algae have developed several mechanisms that help them respond to adverse environments. Non‐photochemical quenching (NPQ) is one of these mechanisms. The thalli of algae in the intertidal zone that are attached to rocks can be subjected to salt stress for a short period of time due to the rise and fall of the tide. Ulva prolifera causes green tides and can form floating mats when green tides occur and the upper part of the thalli is subjected to high salt stress for a long period of time. In this study, we compared the Ulva prolifera photosynthetic activities and NPQ kinetics when it is subjected to different salinities over various periods of time. Thalli exposed to a salinity of 90 for 4 d showed enhanced NPQ, and photosynthetic activities decreased from 60 min after exposure up to 4 d. This indicated that the induction of NPQ in Ulva prolifera under salt stress was closely related to the stressing extent and stressing time. The enhanced NPQ in the treated samples exposed for 4 d may explain why the upper layer of the floating mats formed by Ulva prolifera thalli were able to survive in the harsh environment. Further inhibitor experiments demonstrated that the enhanced NPQ was xanthophyll cycle and transthylakoid proton gradient‐dependent. However, photosystem II subunit S and light‐harvesting complex stress‐related protein didn't over accumulate and may not be responsible for the enhanced NPQ. [ABSTRACT FROM AUTHOR]

Species of the genus Ulva (Chlorophyta) are regarded as opportunistic organisms, which efficiently adjust their metabolism to the prevailing environmental conditions. In this study, changes in chlorophyll‐a fluorescence‐based photoinhibition of photosynthesis, electron transport rates, photosynthetic pigments, lipid peroxidation, total phenolic compounds, and antioxidant metabolism were investigated during a diurnal cycle of natural solar radiation in summer (for 12 h) under two treatments: photosynthetically active radiation (PAR: 400–700 nm) and PAR+ ultraviolet (UV) radiation (280–700 nm). In the presence of PAR alone, Ulva rigida showed dynamic photoinhibition, and photosynthetic parameters and pigment concentrations decreased with the intensification of the radiation. On the other hand, under PAR+UV conditions a substantial decline up to 43% was detected and an incomplete fluorescence recovery, also, P‐I curve values remained low in relation to the initial condition. The phenolic compounds increased their concentration only in UV radiation treatments without showing a correlation with the antioxidant activity. The enzimatic activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX) increased over 2‐fold respect at initial values during the onset of light intensity. In contrast, catalase (CAT) increased its activity rapidly in response to the radiation stress to reach maxima at 10 a.m. and decreasing during solar. The present study suggests that U. rigida is capable of acclimating to natural radiation stress relies on a concerted action of various physiological mechanisms that act at different times of the day and under different levels of environmental stress. [ABSTRACT FROM AUTHOR]

As one of the most abundant and ubiquitous representatives of marine and brackish coastal macrophytobenthos communities, the genus Ulva is not only an important primary producer but also of ecological and morphogenetic interest to many scientists. Ulva mutabilis became an important model organism to study morphogenesis and mutualistic interactions of macroalgae and microorganisms. Here, we report that our collections of Ulva compressa Linnaeus (1753) from Germany are conspecific with the type strains of the model organism U. mutabilis Føyn (1958), which were originally collected at Olhão on the south coast of Portugal and have from that time on been maintained in culture as gametophytic and parthenogenetic lab strains. Different approaches were used to test conspecificity: (i) comparisons of vegetative and reproductive features of cultured material of U. mutabilis and German U. compressa demonstrated a shared morphological pattern; (ii) gametes of U. compressa and U. mutabilis successfully mated and developed into fertile sporophytic first‐generation offspring; (iii) molecular phylogenetics and species delimitation analyses based on the Generalized Mixed Yule‐Coalescent method showed that U. mutabilis isolates (sl‐G[mt+]) and (wt‐G[mt‐]) and U. compressa belong to a unique Molecular Operational Taxonomic Unit. According to these findings, there is sufficient evidence that U. mutabilis and U. compressa should be regarded as conspecific. [ABSTRACT FROM AUTHOR]

Phylogenetic clades based on DNA sequences such as the chloroplast rbcL gene and the nuclear ITS region are frequently used to delimit algal species. However, these molecular markers cannot accurately delimit boundaries among some Ulva species. Although Ulva reticulata and Ulva ohnoi occasionally bloom in tropical to warm‐temperate regions and are clearly distinguishable by their reticulate or plain blade morphology, they have few or no sequence divergences in these molecular markers and form a monophyletic clade. In this study, to clarify the speciation and species delimitation in the U. reticulata‐ohnoi complex clade, reproductive relationships among several sexual strains from the Philippines and Japan including offspring that originated from the type specimen of U. ohnoi were examined by culturing and hybridization in addition to the ITS‐based analysis. As a result, both prezygotic and postzygotic reproductive isolation were revealed to occur between genetically perforated U. reticulata and imperforate U. ohnoi. They were also separated on the basis of sequence analysis of the ITS region. That strongly supports that the two taxa are independent biological species. Although no prezygotic barrier among the Philippine and Japanese strains of U. reticulata was observed, unexpectedly zoospores produced by hybrid sporophytes in some of their combinations mostly failed to develop, indicating partial formation of a postzygotic barrier despite a 0.2% divergence in the ITS sequence. These findings suggest speciation is still ongoing in U. reticulata. [ABSTRACT FROM AUTHOR]

Ulva spp. dominates green tides around the world, which are occurring at an accelerated rate. The competitive nitrogen assimilation efficiency in Ulva is suggested to result in ecological success against other seaweeds. However, molecular characterization of genes involved in nitrogen assimilation has not been conducted. Here, we describe the identification of the nitrate reductase ( NR) gene from a green seaweed Ulva prolifera, an alga which is responsible for the world's largest green tide in the Yellow Sea. Using rapid amplification of cDNA ends and genome walking, the NR gene from U. prolifera ( Up NR) was cloned, which consisted of six introns and seven exons encoding 863 amino acids. According to sequence alignment, the NR in U. prolifera was shown to possess all five essential domains and 21 key invariant residues in plant NRs. The GC content of third codon position of Up NR (82.75%) was as high as those of green microalgae, and the intron number supported a potential loss issue from green microalga to land plant. Real-time quantitative PCR results showed that Up NR transcript level was induced by nitrate and repressed by ammonium, which could not be removed by addition of extra nitrate, indicating that U. prolifera preferred ammonium to nitrate. Urea would not repress NR transcription by itself, while it weakened the induction effect of nitrate, implying it possibly inhibited nitrate uptake rather than nitrate reduction. These results suggest the use of Up NR as a gene-sensor to probe the N assimilation process in green tides caused by Ulva. [ABSTRACT FROM AUTHOR]

To further understand the trends in the evolution of mitochondrial genomes (mitogenomes or mt DNAs) in the Ulvophyceae, the mitogenomes of two separate thalli of Ulva pertusa were sequenced. Two U. pertusa mitogenomes (Up1 and Up2) were 69,333 bp and 64,602 bp in length. These mitogenomes shared two ribosomal RNAs ( rRNAs), 28 transfer RNAs ( tRNAs), 29 protein-coding genes, and 12 open reading frames. The 4.7 kb difference in size was attributed to variation in intron content and tandem repeat regions. A total of six introns were present in the smaller U. pertusa mt DNA (Up2), while the larger mt DNA (Up1) had eight. The larger mt DNA had two additional group II introns in two genes ( cox1 and cox2) and tandem duplication mutations in noncoding regions. Our results showed the first case of intraspecific variation in chlorophytan mitogenomes and provided further genomic data for the undersampled Ulvophyceae. [ABSTRACT FROM AUTHOR]

Members of the genus Ulva are widespread and abundant in intertidal and shallow subtidal areas but there are conflicting data regarding susceptibility to herbivory. While some studies have documented that Ulva spp. were favored by a diversity of marine herbivores, other work has revealed herbivore deterrence. We investigated grazing and growth rates of the littorinid species, Littorina littorea and L. obtusata, when offered Fucus vesiculosus, Ascophyllum nodosum, Ulva lactuca, and Chondrus crispus, highlighting distinctive vulnerabilities to toxic effects of U. lactuca. Ulva lactuca was the preferred food of L. littorea, while L. obtusata showed no grazing on this ephemeral algal species. In contrast, F. vesiculosus was highly preferred by L. obtusata. Although L. littorea demonstrated a grazing preference for U. lactuca, growth rate of this gastropod species was nearly 3× greater when fed F. vesiculosus, suggesting a non-lethal, negative effect of U. lactuca on L. littorea with long-term exposure. Mortality of L. obtusata ranged from 0% to 100% when held in the presence of various Ulva densities for 1 week, and Ulva exudate depressed herbivory of this gastropod. We conclude that the water-soluble, toxic exudate produced by U. lactuca in response to herbivory had allelochemical properties, and may contain a cleavage product (acrylic acid) of dimethylsulfoniopropionate or reactive oxygen species (i.e., H2O2). Observed differences in susceptibility to Ulva toxicity by the littorinid species may be related to generalist versus specialist feeding and habitat strategies. [ABSTRACT FROM AUTHOR]

Free-floating Ulva prolifera is one of the causative species of green tides. When green tides occur, massive mats of floating U. prolifera thalli accumulate rapidly in surface waters with daily growth rates as high as 56%. The upper thalli of the mats experience environmental changes such as the change in carbon source, high salinity, and desiccation. In this study, the photosynthetic performances of PSI and PSII in U. prolifera thalli exposed to different atmospheric carbon dioxide ( CO2) levels were measured. Changes in photosynthesis within salinity treatments and dehydration under different CO2 concentrations were also analyzed. The results showed that PSII activity was enhanced as CO2 increased, suggesting that CO2 assimilation was enhanced and U. prolifera thalli can utilize CO2 in the atmosphere directly, even when under moderate stress. In addition, changes in the proteome of U. prolifera in response to salt stress were investigated. Stress-tolerance proteins appeared to have an important role in the response to salinity stress, whereas the abundance of proteins related to metabolism showed no significant change under low salinity treatments. These findings may be one of the main reasons for the extremely high growth rate of free-floating U. prolifera when green tides occur. [ABSTRACT FROM AUTHOR]

Ulvalean algae (Chlorophyta) are most commonly described from intertidal and shallow subtidal marine environments worldwide, but are less well known from mesophotic environments. Their morphological simplicity and phenotypic plasticity make accurate species determinations difficult, even at the generic level. Here, we describe the mesophotic Ulvales species composition from 13 locations across 2,300 km of the Hawaiian Archipelago. Twenty-eight representative Ulvales specimens from 64 to 125 m depths were collected using technical diving, submersibles, and remotely operated vehicles. Morphological and molecular characters suggest that mesophotic Ulvales in Hawaiian waters form unique communities comprising four species within the genera Ulva and Umbraulva, each with discrete geographic and/or depth-related distributional patterns. Three genetically distinct taxa are supported by both plastid ( rbcL and tufA) and nuclear ( ITS1) markers, and are presented here as new species: Umbraulva kaloakulau, Ulva ohiohilulu, and Ulva iliohaha. We also propose a new Umbraulva species ( Umbraulva kuaweuweu), which is closely related to subtidal records from New Zealand and Australia, but not formally described. To our knowledge, these are the first marine species descriptions from Hawai'i resulting from the collaboration of traditional Hawaiian nomenclature specialists, cultural practitioners and scientists. The difficulty of finding reliable diagnostic morphological characters for these species reflects a common problem worldwide of achieving accurate identification of ulvalean taxa using solely morphological criteria. Mesophotic Ulvales appear to be distinct from shallow-water populations in Hawai'i, but their degree of similarity to mesophotic floras in other locations in the Pacific remains unknown. [ABSTRACT FROM AUTHOR]

A method for the stable transformation of the green marine macroalga Ulva mutabilis was developed based on vector plasmids integrating into the genome. By combination of the expression signals (promoter, enhancer, and transcriptional termination sequences) of a chromosomal rbcS gene from U. mutabilis with the bleomycin resistance gene ( ble) from Streptoalloteichus hindustanus, a dominant selectable marker gene was constructed for the preparation of a series of E. coli- U. mutabilis shuttle vector plasmids. Special vectors were prepared for the introduction and expression of foreign genes in Ulva, for insertional mutagenesis and gene tagging by plasmid integration into the genome, and for protein tagging by the green fluorescent protein, as well as tools for posttranscriptional gene silencing and cosmid cloning to prepare genomic gene libraries for mutant gene complementation. The vectors were successfully tested in pilot experiments, where they were efficiently introduced into Ulva gametes, zoospores or protoplasts of somatic blade cells by treatment with Ca2+-ions and polyethylene glycol under isotonic conditions at low ionic strength. The parthenogenetically propagated phleomycin-resistant transformants of the mutant slender (sl) and the wildtype (wt) were demonstrated to be carrying the plasmids randomly integrated into the chromosomes often as tandem repeat clusters. [ABSTRACT FROM AUTHOR]

The cell-cycle progression of Ulva compressa is diurnally gated at the G1 phase in accordance with light-dark cycles. The present study was designed to examine the spectral sensitivity of the G1 gating system. When blue, red, and green light-emitting diodes ( LEDs) were used for illumination either alone or in combination, the cells divided under all illumination conditions, suggesting that all colors of light were able to open the G1 gate. Although blue light was most effective to open the G1 gate, red light alone or green light alone was also able to open the G1 gate even at irradiance levels lower than the light compensation point of each color. Occurrence of a period of no cell division in the course of a day suggested that the G1 gating system normally functioned as under ordinary illumination by cool-white fluorescent lamps. The rise of the proportion of blue light to green light resulted in increased growth rate. On the other hand, the growth rates did not vary regardless of the proportion of blue light to red light. These results indicate that the difference in growth rate due to light color resulted from the difference in photosynthetic efficiency of the colors of light. However, the growth rates significantly decreased under conditions without blue light. This result suggests that blue light mediates cell elongation and because the spectral sensitivity of the cell elongation regulating system was different from that of the G1 gating system, distinct photoreceptors are likely to mediate the two systems. [ABSTRACT FROM AUTHOR]

Macroalgal bloom-forming species occur in coastal systems worldwide. However, due to overlapping morphologies in some taxa, accurate taxonomic assessment and classification of these species can be quite challenging. We investigated the molecular and morphological characteristics of 153 specimens of bloom-forming Ulva located in and around Narragansett Bay, RI, USA. We analyzed sequences of the nuclear internal transcribed spacer 1 region ( ITS1) and the chloroplast-encoded rbcL; based on the ITS1 data, we grouped the specimens into nine operational taxonomic units ( OTUs). Eight of these OTUs have been previously reported to exist, while one is novel. Of the eight OTUs, all shared sequence identity with previously published sequences or differed by less than 1.5% sequence divergence for two molecular markers. Previously, 10 species names were reported for Ulva in Rhode Island (one blade and nine tube-forming species) based upon morphological classification alone. Of our nine OTUs, three contained blade-forming specimens ( U. lactuca, U. compressa, U. rigida), one OTU had a blade with a tubular stipe, and six contained unbranched and/or branched tubular morphologies (one of these six, U. compressa, had both a blade and a tube morphology). While the three blade-forming OTUs in Narragansett Bay can frequently be distinguished by careful observations of morphological characteristics, and spatial/temporal distribution, it is much more difficult to distinguish among the tube-forming specimens based upon morphology or distribution alone. Our data support the molecular species concept for Ulva, and indicate that molecular-based classifications of Ulva species are critical for proper species identification, and subsequent ecological assessment or mitigation of Ulva blooms. [ABSTRACT FROM AUTHOR]

Ulva Linnaeus ( Ulvophyceae, Ulvales) is a genus of green algae widespread in different aquatic environments. Members of this genus show a very simple morphology and a certain degree of phenotypic plasticity, heavily influenced by environmental conditions, making difficult the delineation of species by morphological features alone. Most studies dealing with Ulva biodiversity in Mediterranean waters have been based only on morphological characters and a modern taxonomic revision of this genus in the Mediterranean is not available. We report here the results of an investigation on the diversity of Ulva in the North Adriatic Sea based on molecular analyses. Collections from three areas, two of which subject to intense shipping traffic, were examined, as well as historical collections of Ulva stored in the Herbarium Patavinum of the University of Padova, Italy. Molecular analyses based on partial sequences of the rbcL and tufA genes revealed the presence of six different species, often with overlapping morphologies: U. californica Wille, U. flexuosa Wulfen, U. rigida C. Agardh , U. compressa Linnaeus, U. pertusa Kjellman, and one probable new taxon. U. californica is a new record for the Mediterranean and U. pertusa is a new record for the Adriatic. Partial sequences obtained from historical collections show that most of the old specimens are referable to U. rigida. No specimens referable to the two alien species were found among the old herbarium specimens. The results indicate that the number of introduced seaweed species and their impact on Mediterranean communities have been underestimated, due to the difficulties in species identification of morphologically simple taxa as Ulva. [ABSTRACT FROM AUTHOR]

Axenic Ulva mutabilis gametes develop parthenogenetically into callus-like colonies consisting of undifferentiated cells without normal cell walls. From the accompanying microbial flora of established laboratory strains of U. mutabilis with normal morphology, a Roseobacter, a Sulfitobacter, and a Halomonas species were isolated. Each of these microbe species alone induced the development of the Ulva gametes into thalli composed of differentiated cells with characteristic deficiencies. Typical traits of these thalli were: an enhanced rate of cell division not followed by cell expansion, the presence of unusual cell wall protrusions, and the absence of differentiated rhizoid cells. The addition of a Cytophaga species, also derived from the same microbial flora, to either one of the three other strains resulted in the development of normal fast growing thalli with the typical morphology of the algal strain used. These effects are mediated by specific regulatory factors that are excreted into the environment by the bacteria and could be also isolated from the bacterial cell extracts. In contrast with the Cytophaga-factor, the regulatory factor of the three other bacterial species was also found intracellularly in other bacterial strains not associated with Ulva, but in this case it was not excreted. Functionally, the Roseobacter-, Sulfitobacter-, and Halomonas-factors resemble a cytokinin, while the Cytophaga-factor acts similar to auxin. Neither factor could be replaced by known phytohormones. The Roseobacter species exhibits a specific chemotactic affinity to the rhizoid cells of U. mutabilis and seems to cooperate with the Cytophaga strain and the alga by chemical communication forming a symbiotic tripartite community. [ABSTRACT FROM AUTHOR]

The present study was designed to develop a technique for crossing and to gain insight into how sexual reproduction contributes to the maintenance of local populations of Ulva compressa L. To examine the durations of gamete motility and conjugation ability, freshly released gametes were incubated for various periods of time prior to mixing both mating types. The conjugation ability of the gametes gradually declined after being released from the thalli when the gametes were incubated without mixing with the opposite mating type. The ability to conjugate decreased by half after 6 h, although most of the gametes remained motile. The gametes released 4 h later had the same level of conjugation ability when mixed immediately after releasing. When the mature thalli were wrapped in a moist paper towel to prevent gametes from being released, the gametes were preservable for 7 h without a significant decrease in their conjugation ability. Conjugation occurred soon after mixing gametes of both mating types and reached a plateau after 30 s. However, conjugation rates did not exceed a rate of ∼70%, even though freshly released gametes were used. Interestingly, a portion of the gametes newly conjugated 30 min after mixing both mating types, and conjugation rates reached a second plateau at ∼90%. Gametes with delayed conjugation are provided some period of time that allows them to be transported away and increases their chances of mating with more distant populations, thus contributing to the maintenance of genetic variation. [ABSTRACT FROM AUTHOR]

The present study was designed to develop a technique for crossing and to gain insight into how sexual reproduction contributes to the maintenance of local populations of Ulva compressa L. To examine the durations of gamete motility and conjugation ability, freshly released gametes were incubated for various periods of time prior to mixing both mating types. The conjugation ability of the gametes gradually declined after being released from the thalli when the gametes were incubated without mixing with the opposite mating type. The ability to conjugate decreased by half after 6 h, although most of the gametes remained motile. The gametes released 4 h later had the same level of conjugation ability when mixed immediately after releasing. When the mature thalli were wrapped in a moist paper towel to prevent gametes from being released, the gametes were preservable for 7 h without a significant decrease in their conjugation ability. Conjugation occurred soon after mixing gametes of both mating types and reached a plateau after 30 s. However, conjugation rates did not exceed a rate of ∼70%, even though freshly released gametes were used. Interestingly, a portion of the gametes newly conjugated 30 min after mixing both mating types, and conjugation rates reached a second plateau at ∼90%. Gametes with delayed conjugation are provided some period of time that allows them to be transported away and increases their chances of mating with more distant populations, thus contributing to the maintenance of genetic variation. [ABSTRACT FROM AUTHOR]

Transcripts and enzyme activities of antioxidative enzymes were increased by hypersalinity (90‰) in a marine macroalga, Ulva fasciata Delile (, ). This study examined the effects of polyamines (PAs) on the induction of hypersalinity tolerance through the modulation of expression of antioxidative defense enzymes. Incubation of U. fasciata grown under 30‰ in the presence of putrescine (Put), spermidine (Spd), or spermine (Spm) (1 mM) for 12 h increased internal PA contents prior to 90‰ treatment. Spd or Spm pretreatments reduced HO accumulation and lipid peroxidation during 90‰ treatment and improved the recovery growth rate after transfer from 90‰ to 30‰. Increases in iron superoxide dismutase (FeSOD; EC 1.15.1.1) activity and transcript levels observed under 90‰ were further increased by Spd and Spm pretreatments, while Put pretreatment had no effect. Increases in MnSOD activity and transcript levels observed under 90‰ were enhanced by Spd and Put pretreatment. An observed increase in catalase (CAT; EC 1.11.1.6) activity and transcript levels under 90‰ was not affected by Spd and Spm pretreatments but was inhibited by Put pretreatment. Observed increases in ascorbate peroxidase (APX; EC 1.11.1.11) activity and transcript levels under 90‰ were inhibited by Put, Spd, and Spm pretreatments. In conclusion, Spd and Spm treatment affords U. fasciata protection against hypersalinity through the up-regulation of FeSOD gene expression, thereby alleviating oxidative damage. [ABSTRACT FROM AUTHOR]

The macroalga Ulva limnetica K. Ichihara et S. Shimada is the only known Ulva species to be distributed exclusively in freshwater and is restricted to freshwater bodies in the Ryuku archipelago. Molecular phylogenetic analysis suggests that U. limnetica originally evolved from marine forms of Ulva. The mechanisms of adaptation to freshwater in Ulva spp. are poorly understood. In this study, we isolated genes potentially involved in adaptation or tolerance to freshwater conditions in U. limnetica, using suppression subtractive hybridization between mRNAs of samples cultured in freshwater and seawater conditions. A total of 219 genes, up-regulated by the exposure of the macroalga to freshwater, were isolated. Reverse transcription-PCR (RT-PCR) revealed 39 clones, including malate dehydrogenase, soluble starch synthase, triosephosphate isomerase, plastid ribosomal protein, DnaJ-like protein, and chloroplast ascorbate peroxidase (APX), which were specifically or preferentially expressed in freshwater conditions. These 39 clones were also analyzed for their temporal transcriptional response to freshwater conditions. A large majority of these up-regulated genes showed a transient peak of expression after 1-4 h, followed in the next 24 h by a decrease to a stable level (over the 7 d of the experiment). After the initial response peak, the level of expression either remained higher than in the control (long-term response) or returned to a level similar to pretreatment level. A few genes showed a more delayed response (i.e., after several days) to freshwater exposure. Finally, we discussed the possible contributions of the freshwater-induced genes in the acquisition of freshwater adaptation or tolerance of U. limnetica. [ABSTRACT FROM AUTHOR]

It has been shown that marine algae produce the compatible solute dimethylsulfoniopropionate (DMSP) from methionine (Met) via four enzymatic reactions in which the third step, synthesis of 4-dimethylsulfonio-2-hydroxy-butyrate (DMSHB) from 4-methylthio-2-hydroxybutyrate (MTHB), is the committing step. However, regulation of the biosynthetic pathways and transport properties of DMSP is largely unknown. Here, the effects of sulfur and sodium concentrations on the uptake and synthesis of DMSHB and DMSP were examined in a sterile mutant of Ulva pertusa Kjellm. Sulfur deficiency increased the activity of the sulfur assimilation enzyme O-acetyl serine sulfhydrylase but decreased the MTHB S-methyltransferase activity, suggesting the preferential utilization of sulfur atoms for Met metabolites other than DMSP. Uptake of DMSP and DMSHB was enhanced by S deficiency. High salinity enhanced the MTHB S-methyltransferase activity as well as the uptake of DMSHB. The MTHB S-methyltransferase activity was inhibited by its product DMSP. These data demonstrate the importance of MTHB S-methyltransferase activity and uptake of DMSHB for the regulation of DMSP. [ABSTRACT FROM AUTHOR]

We quantified the effects of initial macroalgal tissue nitrogen (N) status (depleted and enriched) and varying pulses of nitrate (NO) concentration on uptake and storage of nitrogen in Ulva intestinalis L. and Ulva expansa (Setch.) Setch. et N. L. Gardner using mesocosms modeling shallow coastal estuaries in Mediterranean climates. Uptake of NO (μmol · g dry weight [dwt] · h) was measured as loss from the water after 1, 2, 4, 8, 12, and 24 h and storage as total tissue nitrogen (% dwt) and nitrate (ppm). Both species of algae exhibited a high affinity for NO across all N pulses and initial tissue contents. There was greater NO removal from the water for depleted than enriched algae across all time intervals. In the low-N-pulse treatment, U. intestinalis and U. expansa removed all measurable NO within 8 and 12 h, respectively, and in the medium and high treatments, removal was high and then decreased over time. Maximum mean uptake rates of nitrate were greater for U. expansa (∼300 μmol · g dwt · h) than U. intestinalis (∼100 μmol · g dwt · h); however, uptake rates were highly variable over time. Overall, U. expansa uptake rates were double those of U. intestinalis. Maximum tissue NO for U. expansa was >1,000 ppm, five times that of U. intestinalis, suggesting that U. expansa has a greater storage capacity in this cellular pool. These results showed that opportunistic green algae with differing tissue nutrient histories were able to efficiently remove nitrate from the water across a wide range of N pulses; thus, both are highly adapted to proliferate in estuarine environments with pulsed nutrient supplies. [ABSTRACT FROM AUTHOR]

Appreciation of the true species diversity of the genus Ulva in Australian waters has been blinkered by the unproved assumption that its representatives there are largely cosmopolitan. As species of Ulva are some of the longest-standing and most widely reported taxa of macroalgae, the presumption that they are worldwide in distribution has led to most Australian members being equated with species originally described from extra-Australian type localities. Ulva species can be notoriously difficult to identify due to the few and often variable characters on which classical taxonomic studies focus so that names of specimens in hand, as well as names appearing in historical distribution records, are frequently difficult or impossible to verify. The combination of morphological and molecular analyses, the latter involving both nuclear (internal transcribed spacer [ITS]) and plastid ( rbcL) markers, is critically important in taxonomic studies of the genus and has here been applied to selected Ulva populations from mostly cool-temperate southern Australian localities. It has been determined that habit- and anatomy-based keys of standard taxonomic literature are largely adequate for assigning species names based on classical concepts, but they often obscure a number of cryptic and pseudocryptic species that do not conform to extra-Australian populations of the same designation, as indicated by the corresponding molecular data. Here, we present six species ( Ulva australis Aresch., U. compressa Forssk., U. fasciata Delile, U. intestinalis L., U. laetevirens Aresch., U. tanneri H. S. Hayden et J. R. Waaland) for which anatomical and molecular data were congruent with both classical concepts and GenBank accession data and confirm these as cosmopolitan taxa in Australia. We also present six putative species designations based on anatomy [ U. clathrata (Roth) C. Agardh, U. flexuosa Wulfen, U. linza L., U. prolifera O. F. Müll., U. stenophylla Setch. et N. L. Gardner, U. brisbanensis sp. nov.] that are inconsistent with molecular data, suggesting novel or cryptic taxa not represented in GenBank. [ABSTRACT FROM AUTHOR]

The seaweed Ulva lactuca L. was spray cultured by mariculture effluents in a mattress-like layer, held in air on slanted boards by plastic netting. Air-agitated seaweed suspension tanks were the reference. Growth rate, yield, and ammonia-N removal rate were 11.8% · d−1, 171 g fresh weight (fwt) · m−2 · d−1, and 5 g N · m−2 · d−1, respectively, by the spray-cultured U. lactuca, and 16.9% · d−1, 283 g fwt · m−2 · d−1, and 7 g N · m−2 · d−1, respectively, by the tank U. lactuca. Biomass protein content was similar in both treatments. Dissolved oxygen in the fishpond effluent water was raised by >3 mg · L−1 and pH by up to half a unit, upon passage through both culture systems. The data suggest that spray-irrigation culture of U. lactuca in this simple green-mattress-like system supplies the seaweed all it needs to grow and biofilter at rates close to those in standard air-agitated tank culture. [ABSTRACT FROM AUTHOR]

Sequences of the nuclear internal transcribed spacer 1 (ITS1) region and the chloroplast rbcL gene were obtained from 86 specimens of Ulva (including “ Enteromorpha”) from five of the main Hawaiian Islands. These 86 specimens were divided into 11 operational taxonomic units (OTUs) based on analyses of primary sequence data and comparisons of ITS1 secondary structure. Of the 11 OTUs, six have not previously been reported from anywhere in the world. Only three represented exact sequence matches to named species ( Ulva lactuca L., syn. U. fasciata Delile; U. ohnoi Hiraoka et Shimada); two others represented exact sequence matches to unnamed species from Japan and New Zealand. Of the 12 species names currently in use for Hawaiian Ulva, only one, U. lactuca (as U. fasciata), was substantiated. General morphology of the specimens did not always correspond with molecular OTUs; for example, reticulate thallus morphology, previously considered diagnostic for the species U. reticulata Forssk., was expressed in thalli assigned to U. ohnoi and to one of the novel OTUs. This finding confirms a number of recent studies and provides further support for a molecular species concept for Ulva. These results suggest that Ulva populations in tropical and subtropical regions consist of species that are largely unique to these areas, for which the application of names based on types from temperate and boreal European and North American waters is inappropriate. Ulva ohnoi, a “green tide” species, is reported from Hawaii for the first time. [ABSTRACT FROM AUTHOR]

Gametophytes of Ulva mutabilis Føyn and Ulva lactuca L. were artificially induced to form gametangia by removal of sporulation inhibitors. After this treatment, U. mutabilis gametes were ready for swarming on the third morning after induction, while U. lactuca gametangia needed 1–2 d longer for maturation. Release of gametes of U. lactuca was dependent solely upon exposure to the first light in the morning. Gametangia of U. mutabilis, however, also required sufficient dilution of the swarming inhibitor (SWI). SWI was excreted transiently by both Ulva species early during gametogenesis. While the SWI concentration in U. mutabilis medium remained above the inhibitory concentration until the gametangia were mature, the concentration of U. lactuca-SWI dropped rapidly below this level. In the presence of sufficient SWI, mature gametes of U. mutabilis remained motionless within the gametangia despite light and open exit pores. However, using SEM, an additional seal was detected within these pores, which probably prevented premature swarming until dilution of SWI and exposure to light. Observations by time lapse microscopy and experiments with the myosin kinase inhibitor BDM suggest that the gametes may be either extruded by the gametangium or leave the exit pore by active gliding motion, driven by a myosin-like motor protein. The SWIs were purified from both Ulva species, and mass spectral analysis showed their molecular masses (292 Da) were identical. [ABSTRACT FROM AUTHOR]

A field population of Ulva pseudocurvata Koeman et C. Hoek (hereafter termed Ulva) at Sylt Island (North Sea, Germany) exhibited biweekly peaks of gametophytic reproduction during the colder seasons and approximately weekly peaks during summer. The reproductive events lasted 1–5 d and were separated from each other by purely vegetative phases. Under constant conditions in the laboratory, a free-running rhythm was observed with reproductive peaks occurring approximately every 7 d. When artificial moonlight was provided every 4 weeks, fewer reproductive events occurred, and the reproductive rhythm became synchronized to the environmental artificial moonlight rhythm. In the laboratory, apical disks were entirely converted into reproductive tissue after 8 d cultivation, while almost all basal disks stayed vegetative, which prevented the entire loss of the vegetative thallus during reproductive events. Seasonal size reduction of the thallus occurred from late autumn onward and was determined to be controlled by a genuine photoperiodic response, since size reduction could be induced from May onward by experimental short-day (SD) treatment but was prevented in a long-day (LD) or night-break regime (NB). A daily fine-tuning occurred with gamete release early in the morning at the first sign of daylight, following an obligatory dark (“night”) period of at least 1 h duration. No release took place if the overnight dark phase was replaced by continuous light. Blue, green, or red light all triggered gamete release after a dark phase at an irradiance of 0.1 μmol photons · m−2 ·s−1, while 0.001 μmol photons · m−2 · s−1 was equivalent to a dark control. [ABSTRACT FROM AUTHOR]

There is a general lack of genomic information available for chlorophyte seaweed genera such as Ulva, and in particular there is no information concerning the genes that contribute to adhesion and cell wall biosynthesis for this organism. Partial sequencing of cDNA libraries to generate expressed sequence tags (ESTs) is an effective means of gene discovery and characterization of expression patterns. In this study, a cDNA library was created from sporulating tissue of Ulva linza L. Initially, 650 ESTs were randomly selected from a cDNA library and sequenced from their 5′ ends to obtain an indication of the level of redundancy of the library (21%). The library was normalized to enrich for rarer sequences, and a further 1920 ESTs were sequenced. These sequences were subjected to contig assembly that resulted in a unigene set of approximately 1104 ESTs. Forty-eight percent of these sequences exhibited significant similarity to sequences in the databases. Phylogenetic comparisons are made between selected sequences with similarity in the databases to proteins involved in aspects of extracellular matrix/cell wall assembly and adhesion. [ABSTRACT FROM AUTHOR]

Effects of phosphite (Phi) on phosphate (Pi) starvation responses were determined in Ulva lactuca L. by incubation in Pi-limited (1 μM NaH2PO4) or Pi-sufficient (100 μM NaH2PO4) seawater containing 0–3 mM Phi. Exposure to 1 μM NaH2PO4 decreased the growth rate and the content of free Pi and esterified-P but increased the activities of extracellular alkaline phosphatase (EC 3.1.2.1) and intracellular acid phosphatase (ACP; EC 3.1.2.2); two ACP isozymes observed by activity staining on isoelectric focussing (IEF) gel were induced. The Km value of Pi uptake rate was decreased by incubation with 1 μM NaH2PO4 and the decrease in Km value was inhibited by 2 mM Phi, reflecting the operation of a high-affinity Pi uptake system at low Pi concentrations. In the presence of Phi, the growth rate of Pi-sufficient and Pi-starved thalli decreased as Phi concentrations were increased from 0 to 2 mM. As Phi concentrations were increased from 0 to 2 mM, the free Pi contents in both Pi-sufficient and Pi-starved thalli decreased, but the esterified-P contents in Pi-starved thalli increased, whereas those in Pi-sufficient thalli increased at 1 mM Phi and decreased at 2 mM Phi. Cell wall localized AP activity in both Pi-sufficient and Pi-starved thalli decreased as Phi concentrations were increased from 0 to 2 mM. Intracellular ACP activity in Pi-starved thalli decreased as Phi concentrations were increased from 0 to 2 mM but was not affected in Pi-sufficient thalli. The induction of ACP isozyme activity and high-affinity Pi uptake system in Pi-starved thalli was inhibited by Phi. The present investigation shows that Phi interrupts the sensing mechanisms of U. lactuca to Pi-limiting conditions. [ABSTRACT FROM AUTHOR]

Genomes from over 130 organisms have been either sequenced completely or are currently under investigation. These studies include a wide array of Bacteria, a smaller number of Archaea, model-system eukaryotes, parasitic protists, and even several microalgae. However, no major effort is underway to acquire a complete nuclear genome sequence from a single macroalga or seaweed despite their crucial contribution to the biodiversity and energy economy of oceans and estuaries. Here we examine various macroalgae as potential candidates for a genome project. A set of criteria is presented, followed by a brief discussion of how well different candidates from the principal macroalgae groups, green, brown, and red algae, meet these criteria. Based on our analyses, we conclude that the red seaweed, Porphyra yezoensis Ueda, should be the leading candidate for a macroalgal genomics initiative. We realize, of course, that others in the phycological community might have a different opinion and that a broad consensus among algal researchers is required to make seaweed genomics a reality; thus the primary intention of this review is to initiate and encourage further discussion as to where the phycological community should focus its genomic efforts. [ABSTRACT FROM AUTHOR]

Gross oxygen evolution was compared with the electron transport rate (ETR), estimated from chl a fluorescence parameters on the common tropical green macro alga Ulva fasciata Delile with confirmatory carbon saturation curves from U. reticulata Forskål. Theoretically, the relationship between estimated ETR and gross oxygen evolution should be 4:1, that is, four electrons are transported through PSII for each molecule of oxygen evolved. However, deviations of the 4:1 relationship have previously been reported. Measurements were conducted with two commercially available and portable pulse amplitude modulated (PAM) chl fluorometers. We sought experimental approaches that minimize discrepancies between the two different measuring techniques of photosynthetic rates, both for in situ and laboratory conditions. Using fresh algal tissue for each of the different irradiances gave the best fit of gross oxygen evolution and ETR even at irradiances above light saturation, where large discrepancies between oxygen evolution and ETR are common. With increasing dissolved inorganic carbon (DIC) concentrations, there was a curvilinear response of gross oxygen evolution in relation to ETR. We therefore suggest to establish DIC saturation curves in the laboratory, oxygen evolution is probably the most relevant choice. Photorespiration could not readily explain a curvilinear response of O2 evolution and proportionally higher ETR at high irradiances. ETRs measured with the rapid light curve function of the PAM were compared with steady-state rates of gross and net oxygen evolution, and the ETR was found to decrease at higher irradiances whereas oxygen evolution was constant. [ABSTRACT FROM AUTHOR]