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Kappaphycus alvarezii provides an important raw material for the extraction of κ-carrageenan. Comparative transcriptome analysis of K. alvarezii after 24 h extreme temperature treatments (17°C and 34°C) was performed to uncover the molecular mechanisms controlling temperature-related photosynthesis regulation. Optimum temperature (28°C) was employed as the control. After de novo assembly of these three transcriptome samples and searching the assembled transcripts by BLAST against the NCBI nr databases, 11,537 top-hit transcripts were assigned as unigenes. Through comparisons, 302 significantly differentially expressed genes were identified. Twenty-three of the differentially expressed unigenes encoded photosystem antenna protein subunits and a further 25 were associated more broadly with photosynthesis functions. Compared to the light-harvesting complex (LHC) protein, the expression of phycobiliproteins (PBPs) was stable after extreme low and high temperature (ELT/EHT) treatments. Both ELT and EHT were found to inhibit the expression of subunits of photosystem II (PsbA, PsbC, Psb27, PsbW, PsbS), photosystem I (PsaF, PsaG, PsaK) and photosynthetic electron transport (PetE). These results were confirmed through targeted analysis of the mRNA and protein abundance of individual proteins, and were congruent with the results of chlorophyll a fluorescence (OJIP) measurements performed with temperature-stressed lines. In conclusion, similarities and differences in the behaviours of photosynthesis-related genes were summarized to provide opportunities for understanding the responses of K. alvarezii after extreme temperature treatments. [ABSTRACT FROM AUTHOR]

To understand the effects of low temperature stress on Kappaphycus alvarezii and the responses of antioxidant systems and photosystem II (PSII), behaviour in K. alvarezii thalli exposed to low temperatures (20°C, 17°C and 14°C) for 2 hours was evaluated. Compared with the control at 26°C, activities of some antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD), ascorbate peroxidase (APX) and the level of antioxidant substance (reduced glutathione) increased in K. alvarezii thalli when exposed to lowered temperatures (20°C, 17°C). Hydroxyl free radical (·OH) scavenging activity of K. alvarezii thalli also increased at 20°C and 17°C compared with the control. This indicated that the resistance to low temperature stress in the antioxidant system of K. alvarezii increased at lowered temperatures of 20°C and 17°C. However, at the lowest temperature (14°C), no significant increases of this algal antioxidant were observed. Under low temperature stress, the maximum quantum yield of PSII photochemistry (FV/FM) and PSII actual photochemical efficiency (ΦPSII) decreased in K. alvarezii thalli, suggesting that the photosynthetic capacity declined. Components of the photosynthetic apparatus (such as the oxygen-evolving complex, light absorption antennas, reaction centres, electron acceptor sides and electron donor sides of PSII) were damaged by low temperature stress to varying degrees. In addition, it was found that low temperature stress led to decreases of both D1 protein and Rubisco LSU (Rubisco large subunit) protein levels. This work is a significant contribution towards understanding the basic mechanism involved in the resistance and the adaptation of K. alvarezii to low temperature stress conditions. [ABSTRACT FROM AUTHOR]

Background: Kappaphycus are farmed in tropical countries as raw material for carrageenan, which is widely used in food industry. The sea area available for farming is one limiting factor in the production of seaweeds. Though cultivation is spreading into subtropical regions, the lower seawater temperature is an important problem encountered in subtropical regions for the farming of Kappaphycus. This research of physiological response to low temperature stress will be helpful for screening Kappaphycus strains for growth in a lower temperature environment. Results: Responses of antioxidant systems and photosystem II (PSII) behaviors in Kappaphycus alvarezii and Kappaphycus striatum were evaluated during low temperature treatments (23, 20, 17 °C). Compared with the controls at 26 °C, the HO concentrations increased in both species when the thalli were exposed to low temperatures (23, 20, 17 °C), but these increases were much greater in K. striatum than in K. alvarezii thalli, suggesting that K. striatum suffered more oxidative stress. The activities of some important antioxidant enzymes (e.g. superoxide dismutase and ascorbate peroxidase) and the hydroxyl free radical scavenging capacity were substantially higher at 23, 20 and 17 °C than at the control 26 °C in K. alvarezii, indicating that the antioxidant system of K. alvarezii enhanced its resistance to low temperature. However, no significant increases of antioxidant enzymes activities were observed at 20 and 17 °C in K. striatum. In addition, both the maximal efficiency of PSII photochemistry (F/F) and the performance index (PI) decreased significantly in K. striatum at 23 °C, indicating that the photosynthetic apparatus was damaged at 23 °C. In contrast, no significant decreases of either F/F or PI were observed in K. alvarezii at 23 °C. Conclusions: It is concluded that K. alvarezii has greater tolerance to low temperature than K. striatum. [ABSTRACT FROM AUTHOR]

Photosynthetic parameters, including net O2evolution, pigment content and fast chlorophylla(Chla) fluorescence kinetics, were studied in mature thalli ofGelidium amansii, a marine agar-producing red seaweed, exposed to different salinities (0–35 psu) for 10 days. The results showed that the net O2evolution at 25–32 psu was unchanged, but significantly decreased at either lower or higher salinities. Hypo-saline (15 psu and below) and hyper-saline (35 psu) conditions induced significant losses of Chla, carotenoids and phycobiliproteins, which correlated with the decrease in the absorption flux per cross-section of fronds (ABS/CSo). Polyphasic fluorescence transients revealed that salinities at 10 and 35 psu both caused multiple effects on photosynthetic electron transport. Algae exposed to low salinity at 10 psu showed extensive damage to the donor side of the oxygen-evolving complex (OEC), reaction centre and acceptor side of PSII. Data on net O2evolution showed that 35 psu salinity was more destructive than 10 psu, with the absence of marked osmotic injury to the OEC. The results of this study indicate the possibility ofG. amansiicultivation in estuarine waters with 20–32 psu salinity. [ABSTRACT FROM AUTHOR]

The transcriptome ofKappaphycus alvareziiwas profiled using high-throughput Solexa paired-end sequencing technology. A total of 61 million sequencing reads was generated by filtering the low-quality reads, and 28 701 unigenes with a mean length of 901 bp were obtained based onde novoassembly. In similarity alignments against the NCBI non-redundant protein sequence (NR) database, Swissprot database, Cluster of Orthologous Groups (COG) database, Gene ontology (GO) database, and Kyoto Encyclopedia of Genes and Genomes (KEGG) database, 11 996 (41.79%) unigenes were identified with significant hits (E-value < 10−5) against existing genes. Functional annotation with the KEGG pathway database identified 8975 unigenes and mapped to 125 pathways. Through functional enrichment analysis of the genes with a higher expression value than the average RPKM (reads per kilobase per million reads), we found that some important pathways were highly expressed. The substantial number of transcript sequences ofK. alvareziiprovides a valuable resource for potential gene identification and comparative genomic studies. [ABSTRACT FROM PUBLISHER]

The kappa-carrageenan-producing seaweed Kappaphycus striatus is different from K. alvarezii in that it grows well in the intertidal zone, where the thalli are exposed periodically to dehydration and rehydration. To investigate the specific tolerance mechanism of K. striatus, the photosynthetic behaviour of K. alvarezii and K. striatus exposed to osmotic variation was compared. K. striatus had a lower dehydration rate in the dark treatments and a higher rehydration rate in both the dark and light treatments as compared with K. alvarezii. The FV/FM of K. striatus was significantly higher than that of K. alvarezii during the process of dehydration and rehydration in both the light and dark treatments. The increase in amplitude of JIP-test fluorescence parameters VK, VJ and VI of K. striatus was smaller than that of K. alvarezii during the dehydration process in both the light and dark treatments. The increased amplitude of VK, VJ and VI in K. striatus was significantly lower than that in K. alvarezii when they were rehydrated in the dark treatments. Therefore, during the process of dehydration and rehydration, the tolerance of the oxygen evolving complex, the ability to balance photosynthetic light absorption and energy utilization, as well as the tolerance of PSII reaction centres were relatively higher in K. striatus compared with K. alvarezii. Such an increased tolerance of PSII may help to improve the tolerance of the whole plant to dehydration. [ABSTRACT FROM AUTHOR]

Gelidium amansii , a commercial marine red alga, yields agar of excellent quality, but thus far its cultivation has been unsuccessful. Effects of temperature, especially high temperature, on the photosynthetic performance of this alga are poorly understood. The responses of net O 2 evolution and pigment content in mature thalli exposed to various temperatures of 14, 18, 22, 26, and 30 °C for 2 days were studied. Fast Chl-a fluorescence kinetics and RuBPCase activity of plants exposed to 30 °C for 6, 12, 24, and 48 h were also determined. The results showed that 14–26 °C favored the net O 2 evolution of G. amansii , which ranged from 0.50 to 1.53 μmol O 2 ∙g−1∙min−1. High temperature (30 °C) decreases the contents of Chl-a and carotenoids. Phycobiliproteins increased in the thalli treated for 12 h and longer at 30 °C, suggesting that phycobiliproteins might play an important role in alleviation of oxidative damage caused by high temperature. In addition, the carbon assimilation process, light harvesting pigments, PSII reaction centers, and PSII acceptor side of G. amansii were damaged under 30 °C at 12 h; however, the PSII acceptor side was relatively stable during the initial 24 h treatment. At 30 °C both PSII photochemistry and carbon assimilation were negatively affected and impacted the photosynthetic response of G. amansii. RuBPCase activity showed a stronger positive correlation with photosynthetic oxygen release than the photochemistry. The results of this study confirm that the optimal temperature for G. amansii photosynthesis is between 22 °C to 26 °C and high temperatures of 30 °C and above limit G. amansii growth in near-shore waters. • Temperature played an important role in adjusting the photosynthesis of Gelidium amansii. • Hyperthermic stress of 30 °C was quickly lethal to G. amansii. • Oxygen-evolving complex displayed a higher tolerance to heat stress than the donor side of PSII. • RUBPCase activity was also inhibited by 30 °C stress. [ABSTRACT FROM AUTHOR]