G-Quadruplex in Gene Encoding Large Subunit of Plant RNA Polymerase II: A Billion-Year-Old Story.

G-quadruplexes have long been perceived as rare and physiologically unimportant nucleic acid structures. However, several studies have revealed their importance in molecular processes, suggesting their possible role in replication and gene expression regulation. Pathways involving G-quadruplexes are intensively studied, especially in the context of human diseases, while their involvement in gene expression regulation in plants remains largely unexplored. Here, we conducted a bioinformatic study and performed a complex circular dichroism measurement to identify a stable G-quadruplex in the gene RPB1, coding for the RNA polymerase II large subunit. We found that this G-quadruplex-forming locus is highly evolutionarily conserved amongst plants sensu lato (Archaeplastida) that share a common ancestor more than one billion years old. Finally, we discussed a new hypothesis regarding G-quadruplexes interacting with UV light in plants to potentially form an additional layer of the regulatory network.

Photosynthesis of the Cyanidioschyzon merolae cells in blue, red, and white light.

Photosynthesis and respiration rates, pigment contents, CO2 compensation point, and carbonic anhydrase activity in Cyanidioschizon merolae cultivated in blue, red, and white light were measured. At the same light quality as during the growth, the photosynthesis of cells in blue light was significantly lowered, while under red light only slightly decreased as compared with white control. In white light, the quality of light during growth had no effect on the rate of photosynthesis at low O2 and high CO2 concentration, whereas their atmospheric level caused only slight decrease. Blue light reduced markedly photosynthesis rate of cells grown in white and red light, whereas the effect of red light was not so great. Only cells grown in the blue light showed increased respiration rate following the period of both the darkness and illumination. Cells grown in red light had the greatest amount of chlorophyll a, zeaxanthin, and ß-carotene, while those in blue light had more phycocyanin. The dependence on O2 concentration of the CO2 compensation point and the rate of photosynthesis indicate that this alga possessed photorespiration. Differences in the rate of photosynthesis at different light qualities are discussed in relation to the content of pigments and transferred light energy together with the possible influence of related processes. Our data showed that blue and red light regulate photosynthesis in C. merolae for adjusting its metabolism to unfavorable for photosynthesis light conditions.

Elevated CO2 concentration alleviates UVR-induced inhibition of photosynthetic light reactions and growth in an intertidal red macroalga.

The commercially important red macroalga Pyropia (formerly Porphyra) yezoensis is, in its natural intertidal environment, subjected to high levels of both photosynthetically active and ultraviolet radiation (PAR and UVR, respectively). In the present work, we investigated the effects of a plausibly increased global CO2 concentration on quantum yields of photosystems II (PSII) and I (PSI), as well as photosynthetic and growth rates of P. yezoensis grown under natural solar irradiance regimes with or without the presence of UV-A and/or UV-B. Our results showed that the high-CO2 treatment (~1000 µbar, which also caused a drop of 0.3 pH units in the seawater) significantly increased both CO2 assimilation rates (by 35%) and growth (by 18%), as compared with ambient air of ~400 µbar CO2. The inhibition of growth by UV-A (by 26%) was reduced to 15% by high-CO2 concentration, while the inhibition by UV-B remained at ~6% under both CO2 concentrations. Homologous results were also found for the maximal relative photosynthetic electron transport rates (rETRmax), the maximum quantum yield of PSII (Fv/Fm), as well as the midday decrease in effective quantum yield of PSII (YII) and concomitant increased non-photochemical quenching (NPQ). A two-way ANOVA analysis showed an interaction between CO2 concentration and irradiance quality, reflecting that UVR-induced inhibition of both growth and YII were alleviated under the high-CO2 treatment. Contrary to PSII, the effective quantum yield of PSI (YI) showed higher values under high-CO2 condition, and was not significantly affected by the presence of UVR, indicating that it was well protected from this radiation. Both the elevated CO2 concentration and presence of UVR significantly induced UV-absorbing compounds. These results suggest that future increasing CO2 conditions will be beneficial for photosynthesis and growth of P. yezoensis even if UVR should remain at high levels.

Physiological and biochemical responses driven by different UV-visible radiation in Osmundea pinnatifida (Hudson) Stackhouse (Rhodophyta).

Light, or visible radiation, serves as a source of energy for photosynthesis of plants and most algae. In addition, light and ultraviolet radiation (UV-A and UV-B) act as a biological signal, triggering several cellular processes that are mediated by photoreceptors. The aim of this study was to evaluate the physiological and biochemical responses of Osmundea pinnatifida driven by different radiations through putative photoreceptors. For this, O. pinnatifida was grown under different radiation treatments composed by high intensity of light emitted by a low pressure sodium lamp (SOX), aiming to saturate photosynthesis, which was supplemented by low intensities of visible (red, green and blue) and ultraviolet radiation (UV-A and UV-B), in order to activate photoreceptors. Growth rates, photosynthesis, antioxidant activity, polyphenols, soluble proteins, phycobiliproteins, mycosporine-like amino acids (MAAs) and carotenoids were evaluated during the experiment. Complementary UV-A radiation positively influenced growth rates after 15 days of experiment, although the presence of a peak of blue light in this treatment can also have contributed. UV-B radiation increased the concentration of zeaxanthin and chlorophyll a. The blue light caused the accumulation of chlorophyll a, violaxanthin, phycoerythrin and polyphenols on different days of the experiment. Phycoerythrin also increased under green and red light conditions. Our results showed that some compounds can be modulated by different radiation, and the involvement of photoreceptors is suggested. In red algae, photoreceptors sensitive to red, green and blue light have been identified, however little is known about UV photoreceptors. The presence of photoreceptors sensitive to UV radiation in O. pinnatifida is discussed.

Day/Night Separation of Oxygenic Energy Metabolism and Nuclear DNA Replication in the Unicellular Red Alga Cyanidioschyzon merolae.

The transition from G1 to S phase and subsequent nuclear DNA replication in the cells of many species of eukaryotic algae occur predominantly during the evening and night in the absence of photosynthesis; however, little is known about how day/night changes in energy metabolism and cell cycle progression are coordinated and about the advantage conferred by the restriction of S phase to the night. Using a synchronous culture of the unicellular red alga Cyanidioschyzon merolae, we found that the levels of photosynthetic and respiratory activities peak during the morning and then decrease toward the evening and night, whereas the pathways for anaerobic consumption of pyruvate, produced by glycolysis, are upregulated during the evening and night as reported recently in the green alga Chlamydomonas reinhardtii Inhibition of photosynthesis by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) largely reduced respiratory activity and the amplitude of the day/night rhythm of respiration, suggesting that the respiratory rhythm depends largely on photosynthetic activity. Even when the timing of G1/S-phase transition was uncoupled from the day/night rhythm by depletion of retinoblastoma-related (RBR) protein, the same patterns of photosynthesis and respiration were observed, suggesting that cell cycle progression and energy metabolism are regulated independently. Progression of the S phase under conditions of photosynthesis elevated the frequency of nuclear DNA double-strand breaks (DSB). These results suggest that the temporal separation of oxygenic energy metabolism, which causes oxidative stress, from nuclear DNA replication reduces the risk of DSB during cell proliferation in C. merolaeIMPORTANCE Eukaryotes acquired chloroplasts through an endosymbiotic event in which a cyanobacterium or a unicellular eukaryotic alga was integrated into a previously nonphotosynthetic eukaryotic cell. Photosynthesis by chloroplasts enabled algae to expand their habitats and led to further evolution of land plants. However, photosynthesis causes greater oxidative stress than mitochondrion-based respiration. In seed plants, cell division is restricted to nonphotosynthetic meristematic tissues and populations of photosynthetic cells expand without cell division. Thus, seemingly, photosynthesis is spatially sequestrated from cell proliferation. In contrast, eukaryotic algae possess photosynthetic chloroplasts throughout their life cycle. Here we show that oxygenic energy conversion (daytime) and nuclear DNA replication (night time) are temporally sequestrated in C. merolae This sequestration enables "safe" proliferation of cells and allows coexistence of chloroplasts and the eukaryotic host cell, as shown in yeast, where mitochondrial respiration and nuclear DNA replication are temporally sequestrated to reduce the mutation rate.

Different Photosynthetic Responses of Pyropia yezoensis to Ultraviolet Radiation Under Changing Temperature and Photosynthetic Active Radiation Regimes.

Macroalgae play a crucial role in coastal marine ecosystems, but they are also subject to multiple challenges due to tidal and seasonal alterations. In this work, we investigated the photosynthetic response of Pyropia yezoensis to ultraviolet radiation (PAR: 400-700 nm; PAB: 280-700 nm) under changing temperatures (5, 10 and 15°C) and light intensities (200, 500 and 800 µmol photons m-2  s-1 ). Under low light intensity (200 µmol photons m-2  s-1 ), P. yezoensis showed the lowest sensitivity to ultraviolet radiation, regardless of temperature. However, higher temperatures inhibited the repair rates (r) and damage rates (k) of photosystem II (PSII) in P. yezoensis. However, under higher light intensities (500 and 800 µmol photons m-2  s-1 ), P. yezoensis showed higher sensitivity to UV radiation. Both r and the ratio of repair rate to damage rate (r:k) were significantly inhibited in P. yezoensis by PAB, regardless of temperature. In addition, higher temperatures significantly decreased the relative UV-inhibition rates, while an increased carbon fixation rate was found. Our study suggested that higher light intensities enhanced the sensitivity to UV radiation, while higher temperatures could relieve the stress caused by high light intensity and UV radiation.

Effects of Ultraviolet Radiation (UV-A+UV-B) on the Antioxidant Metabolism of the Red Macroalga Species Acanthophora spicifera (Rhodophyta, Ceramiales) From Different Salinity and Nutrient Conditions.

Acanthophora spicifera (M.Vahl) Børgesen is a macroalga of great economic importance. This study evaluated the antioxidant responses of two algal populations of A. spicifera adapted to different abiotic conditions when exposed to ultraviolet-A+ultraviolet-B radiation (UV-A+UV-B). Experiments were performed using the water at two collection points for 7 days of acclimatization and 7 days of exposure to UVR (3 h per day), followed by metabolic analyses. At point 1, water of 30 ± 1 practical salinity unit (psu) had concentrations of 1.06 ± 0.27 mm NH 4 + , 8.47 ± 0.01 mm NO 3 - , 0.17 ± 0.01 mm PO 4 - 3 and pH 7.88. At point 2, water of 35 ± 1 psu had concentrations of 1.13 ± 0.05 mm NH 4 + , 3.73 ± 0.01 mm NO 3 - , 0.52 ± 0.01 mm PO 4 - 3 and pH 8.55. Chlorophyll a, phycobiliproteins, carotenoids, mycosporins, polyphenolics and antioxidant enzymes (catalase, superoxide dismutase and guaiacol peroxidase) were evaluated. The present study demonstrates that ultraviolet radiation triggers antioxidant activity in the A. spicifera. However, such activation resulted in greater responses in samples of the point 1, with lower salinity and highest concentration of nutrients.

A Simple Procedure to Observe Phototropic Responses in the Red Seaweed Pyropia yezoensis.

The marine red seaweed Pyropia yezoensis exhibits phototropic responses in gametophyte and conchosporangia phases, but not in sporophytes. These responses are easily monitored with a simple culturing box that has one side open to allow for unilateral light irradiation within an incubator. Confirmation of phototropic responses is achieved by changing the direction of unilateral light irradiation via rotation of the culture dishes clockwise 90°.

Ecophysiological responses of a threatened red alga to increased irradiance in an in situ transplant experiment.

The red alga Gelidium corneum is a dominant foundation species in the south-eastern Bay of Biscay, where a decline in its populations has been documented in the few last decades. We investigated the ecophysiological responses of G. corneum to different light conditions by means of an in situ transplant experiment. We found that the stress response measured by physiological and biochemical approaches was higher in G. corneum at higher irradiance levels, for both transplanted and control specimens, than under lower light intensities. In the former case the specimens showed a decrease in maximum quantum yield (Fv/Fm), maximum electron transport rate (ETRmax), photosynthetic efficiency (αETR), photosynthetic pigment contents, nitrogen content and thallus length, whereas the C:N ratio, MAAs and bleaching cover increased. In general terms, these responses were more evident in the apical parts of the thallus than in middle ones. Our results suggest that high light stress at depths of 3 m triggered photobiological changes in G. corneum, involving ineffective photoprotection and the occurrence of chronic photoinhibition. Therefore, considering the upward trend in summer mean surface solar radiation in the study area since the 80s, high light conditions may have played a role in the declines observed in G. corneum beds from the south-eastern Bay of Biscay.

Effects of Ultraviolet Radiation (UVA + UVB) on Germination of Carpospores of the Red Macroalga Pyropia acanthophora var. brasiliensis (Rhodophyta, Bangiales): Morphological Changes.

Carpospores of Pyropia acanthophora var. brasiliensis are dispersion and reproduction units responsible for giving rise to the diploid filamentous structure of this alga's life cycle. The present study assesses the anthropogenic impact of ultraviolet radiation (UVR) on morphology and ultrastructure, spore viability, autofluorescence of chloroplasts and the amount of intensity of ROS during the germination of carpospores. Carpospores were cultivated at 24 ± 1°C, 40 ± 10 µmol photons m-2  s-1 with photoperiod of 12 h and exposed to UVAR + UVBR for 3 h a day for 2 days with a daily dose of 5.05 J cm-2 for UVAR and 0.095 J cm-2 for UVBR. Samples were cultured for another five days exposed only to PAR in order to confirm their viability after the initial 2-day exposure. Carpospores showed significant sensitivity to UVR exposure after only 48 h, including changes in developmental rate, overall morphology, cell organization and chloroplast autofluorescence. UVR exposure inhibited germ tube formation in carpospores, which were mostly nonviable and/or altered, showing retracted cytoplasm and disorganized cytoplasmic content. Even in the absence of UVR exposure, carpospores remained collapsed, indicating irreversible damage. It can be concluded that UVR is a limiting factor for the development of P. acanthophora.

Selective loss of photosystem I and formation of tubular thylakoids in heterotrophically grown red alga Cyanidioschyzon merolae.

We previously found that glycerol is required for heterotrophic growth in the unicellular red alga Cyanidioschyzon merolae. Here, we analyzed heterotrophically grown cells in more detail. Sugars or other organic substances did not support the growth in the dark. The growth rate was 0.4 divisions day-1 in the presence of 400 mM glycerol, in contrast with 0.5 divisions day-1 in the phototrophic growth. The growth continued until the sixth division. Unlimited heterotrophic growth was possible in the medium containing DCMU and glycerol in the light. Light-activated heterotrophic culture in which cells were irradiated by intermittent light also continued without an apparent limit. In the heterotrophic culture in the dark, chlorophyll content drastically decreased, as a result of inability of dark chlorophyll synthesis. Photosynthetic activity gradually decreased over 10 days, and finally lost after 19 days. Low-temperature fluorescence measurement and immunoblot analysis showed that this decline in photosynthetic activity was mainly due to the loss of Photosystem I, while the levels of Photosystem II and phycobilisomes were maintained. Accumulated triacylglycerol was lost during the heterotrophic growth, while keeping the overall lipid composition. Observation by transmission electron microscopy revealed that a part of thylakoid membranes turned into pentagonal tubular structures, on which five rows of phycobilisomes were aligned. This might be a structure that compactly conserve phycobilisomes and Photosystem II in an inactive state, probably as a stock of carbon and nitrogen. These results suggest that C. merolae has a unique strategy of heterotrophic growth, distinct from those found in other red algae.

Ecophysiological implications of UV radiation in the interspecific interaction of Pyropia acanthophora and Grateloupia turuturu (Rhodophyta).

Radiation, both photosynthetic active radiation (PAR, l = 400-700 nm) and Ultraviolet (UVR, l = 280-400 nm) is one of the key factors regulating algal distribution in aquatic environments. Pyropia acanthophora and Grateloupia turuturu have been found over upper rocky shore areas in Southern Brazil, occupying the same niche space. The first species is native and the second one is exotic and considered a potential invader of South Atlantic. The aim of the present study was to evaluate the effects of radiation on physiological responses of both species and infer mechanisms that allow their niche competition in the environment. Samples were cultured in the following conditions: associated or separated, and with an addition of PAR, PAR + UVA (PA) and PAR + UVA + UVB (PAB), totalizing six factorial treatments during 5 days of exposure. Photosynthetic responses of Fv/Fm and ETR were daily evaluated. At the beginning and at the end of the experiment, samples were analyzed for pigment content (chlorophyll a and phycobiliproteins), and mycosporine-like amino acids (MAAs), while oxygen evolution was evaluated at the end of the experiment. As the main results, G. turuturu died when cultivated in PAB conditions. P. acanthophora presented higher amounts of chlorophyll a than G. turuturu during the whole experiment. Phycoerythrin and Fv/Fm remained constant in P. acanthophora but diminished for G. turuturu in UV treatments. ETR was higher for samples that were cultivated in associative treatment. The presence of G. turuturu in the same flask enhanced MAA synthesis in P. acanthophora, regardless of radiation condition. In addition, UV radiation can be a factor controlling species distribution and could counteract the spreading of invasive species, like G. turuturu, allowing P. acanthophora survival in upper rocky shore zones of the natural ecological distribution area.

Impacts of light limitation on corals and crustose coralline algae.

Turbidity associated with elevated suspended sediment concentrations can significantly reduce underwater light availability. Understanding the consequences for sensitive organisms such as corals and crustose coralline algae (CCA), requires an understanding of tolerance levels and the time course of effects. Adult colonies of Acropora millepora and Pocillopora acuta, juvenile P. acuta, and the CCA Porolithon onkodes were exposed to six light treatments of ~0, 0.02, 0.1, 0.4, 1.1 and 4.3 mol photons m-2 d-1, and their physiological responses were monitored over 30 d. Exposure to very low light (<0.1 mol photons m-2 d-1) caused tissue discoloration (bleaching) in the corals, and discolouration (and partial mortality) of the CCA, yielding 30 d EI10 thresholds (irradiance which results in a 10% change in colour) of 1.2-1.9 mol photons m-2 d-1. Recent monitoring studies during dredging campaigns on a shallow tropical reef, have shown that underwater light levels very close (~500 m away) from a working dredge routinely fall below this value over 30 d periods, but rarely during the pre-dredging baseline phase. Light reduction alone, therefore, constitutes a clear risk to coral reefs from dredging, although at such close proximity other cause-effect pathways, such as sediment deposition and smothering, are likely to also co-occur.

A MYB-type transcription factor, MYB2, represses light-harvesting protein genes in Cyanidioschyzon merolae.

While searching for transcriptional regulators that respond to changes in light regimes, we identified a MYB domain-containing protein, MYB2, that accumulates under dark and other conditions in the unicellular red alga Cyanidioschyzon merolae. The isolation and analysis of a MYB2 mutant revealed that MYB2 represses the expression of the nuclear-encoded chloroplast RNA polymerase sigma factor gene SIG2, which results in the repression of the chloroplast-encoded phycobilisome genes that are under its control. Since nuclear-encoded phycobilisome and other light-harvesting protein genes are also repressed by MYB2, we conclude that MYB2 has a role in repressing the expression of light-harvesting genes. The MYB2 mutant is sensitive to a prolonged dark incubation, indicating the importance of MYB2 for cell viability in the dark.

Temperature-Induced Remodeling of the Photosynthetic Machinery Tunes Photosynthesis in the Thermophilic Alga Cyanidioschyzon merolae.

The thermophilic alga C. merolae thrives in extreme environments (low pH and temperature between 40°C and 56°C). In this study, we investigated the acclimation process of the alga to a colder temperature (25°C). A long-term cell growth experiment revealed an extensive remodeling of the photosynthetic apparatus in the first 250 h of acclimation, which was followed by cell growth to an even higher density than the control (grown at 42°C) cell density. Once the cells were shifted to the lower temperature, the proteins of the light-harvesting antenna were greatly down-regulated and the phycobilisome composition was altered. The amount of PSI and PSII subunits was also decreased, but the chlorophyll to photosystems ratio remained unchanged. The 25°C cells possessed a less efficient photon-to-oxygen conversion rate and require a 2.5 times higher light intensity to reach maximum photosynthetic efficiency. With respect to chlorophyll, however, the photosynthetic oxygen evolution rate of the 25°C culture was 2 times higher than the control. Quantitative proteomics revealed that acclimation requires, besides remodeling of the photosynthetic apparatus, also adjustment of the machinery for protein folding, degradation, and homeostasis. In summary, these remodeling processes tuned photosynthesis according to the demands placed on the system and revealed the capability of C. merolae to grow under a broad range of temperatures.

RNA-seq analysis of the transcriptional response to blue and red light in the extremophilic red alga, Cyanidioschyzon merolae.

Light is one of the main environmental cues that affects the physiology and behavior of many organisms. The effect of light on genome-wide transcriptional regulation has been well-studied in green algae and plants, but not in red algae. Cyanidioschyzon merolae is used as a model red algae, and is suitable for studies on transcriptomics because of its compact genome with a relatively small number of genes. In addition, complete genome sequences of the nucleus, mitochondrion, and chloroplast of this organism have been determined. Together, these attributes make C. merolae an ideal model organism to study the response to light stimuli at the transcriptional and the systems biology levels. Previous studies have shown that light significantly affects cell signaling in this organism, but there are no reports on its blue light- and red light-mediated transcriptional responses. We investigated the direct effects of blue and red light at the transcriptional level using RNA-seq. Blue and red lights were found to regulate 35 % of the total genes in C. merolae. Blue light affected the transcription of genes involved in protein synthesis while red light specifically regulated the transcription of genes involved in photosynthesis and DNA repair. Blue or red light regulated genes involved in carbon metabolism and pigment biosynthesis. Overall, our data showed that red and blue light regulate the majority of the cellular, cell division, and repair processes in C. merolae.

Computational Visual Stress Level Analysis of Calcareous Algae Exposed to Sedimentation.

This paper presents a machine learning based approach for analyses of photos collected from laboratory experiments conducted to assess the potential impact of water-based drill cuttings on deep-water rhodolith-forming calcareous algae. This pilot study uses imaging technology to quantify and monitor the stress levels of the calcareous algae Mesophyllum engelhartii (Foslie) Adey caused by various degrees of light exposure, flow intensity and amount of sediment. A machine learning based algorithm was applied to assess the temporal variation of the calcareous algae size (∼ mass) and color automatically. Measured size and color were correlated to the photosynthetic efficiency (maximum quantum yield of charge separation in photosystem II, [Formula: see text]) and degree of sediment coverage using multivariate regression. The multivariate regression showed correlations between time and calcareous algae sizes, as well as correlations between fluorescence and calcareous algae colors.

Differential responses of tetrasporophytes and gametophytes of Mazzaella laminarioides (Gigartinales, Rhodophyta) under solar UV radiation.

The effects of solar UV radiation on mycosporine-like amino acids (MAAs), growth, photosynthetic pigments (Chl a, phycobiliproteins), soluble proteins (SP), and C and N content of Mazzaella laminarioides tetrasporophytes and gametophytes were investigated. Apical segments of tetrasporophytes and gametophytes were exposed to solar radiation under three treatments (PAR [P], PAR+UVA [PA], and PAR+UVA+UVB [PAB]) during 18 d in spring 2009, Punta Arenas, Chile. Samples were taken after 2, 6, 12, and 18 d of solar radiation exposure. Most of the parameters assessed on M. laminarioides were significantly influenced by the radiation treatment, and both gametophytes and tetrasporophytes seemed to respond differently when exposed to high UV radiation. The two main effects promoted by UV radiation were: (i) higher synthesis of MAAs in gametophytes than tetrasporophytes at 2 d, and (ii) a decrease in phycoerythrin, phycocyanin, and SPs, but an increase in MAA content in tetrasporophytes at 6 and 12 d of culture. Despite some changes that were observed in biochemical parameters in both tetrasporophytes and gametophytes of M. laminarioides when exposed to UVB radiation, these changes did not promote deleterious effects that might interfere with the growth in the long term (18 d). The tolerance and resistance of M. laminarioides to higher UV irradiance were expected, as this intertidal species is exposed to variation in solar radiation, especially during low tide.

In silico characterization of DNA motifs associated with the differential expression of the ornithine decarboxylase gene during in vitro cystocarp development in the red seaweed Grateloupia imbricata.

To gain a better understanding of the regulatory mechanism(s) modulating expression of the ornithine decarboxylase gene ODC during cystocarp development in the red seaweed Grateloupia imbricata, DNA motifs found in the 5'-upstream region of the gene were identified by in silico analysis. In addition, when infertile G. imbricata thalli were treated with ethylene, methyl jasmonate, or light as an elicitor of cystocarp development, different ODC expression patterns were observed. ODC expression correlated with (i) the elicitation (treatment) period and the period post-treatment just prior to observation of the first visible developing cystocarps (disclosure period), and (ii) the type of elicitor. Ethylene and light activated ODC expression during the elicitation period, and methyl jasmonate activated its expression during the disclosure period, suggesting that initiation and cystocarp development may involve more than one signaling pathway. In addition, expression of ODC was 450-fold greater when thalli were stimulated by ethylene compared with untreated control thalli, suggesting that G. imbricata mounts an efficient response to sense and activate ethylene-responsive signaling pathways. The patterns of differential ODC expression induced by the different elicitors during cystocarp development might provide an useful tool for characterizing the precise transcriptional regulation of ODC in G. imbricata.

Photosynthetic Performance of the Red Alga Pyropia haitanensis During Emersion, With Special Reference to Effects of Solar UV Radiation, Dehydration and Elevated CO2 Concentration.

Macroalgae distributed in intertidal zones experience a series of environmental changes, such as periodical desiccation associated with tidal cycles, increasing CO2 concentration and solar UVB (280-315 nm) irradiance in the context of climate change. We investigated how the economic red macroalga, Pyropia haitanensis, perform its photosynthesis under elevated atmospheric CO2 concentration and in the presence of solar UV radiation (280-400 nm) during emersion. Our results showed that the elevated CO2 (800 ppmv) significantly increased the photosynthetic carbon fixation rate of P. haitanensis by about 100% when the alga was dehydrated. Solar UV radiation had insignificant effects on the net photosynthesis without desiccation stress and under low levels of sunlight, but significantly inhibited it with increased levels of desiccation and sunlight intensity, to the highest extent at the highest levels of water loss and solar radiation. Presence of UV radiation and the elevated CO2 acted synergistically to cause higher inhibition of the photosynthetic carbon fixation, which exacerbated at higher levels of desiccation and sunlight. While P. haitanensis can benefit from increasing atmospheric CO2 concentration during emersion under low and moderate levels of solar radiation, combined effects of elevated CO2 and UV radiation acted synergistically to reduce its photosynthesis under high solar radiation levels during noon periods.