Tong Pang

Efficacy of binary combinations of botanical pesticides for rotifer elimination in microalgal cultivation

Binary interactions of celangulin, matrine and toosendanin against the rotifer Brachionus plicatilis were studied. Types of interactions (antagonism, synergism and addition) were dependent on the biocides themselves and their ratios in combinations. Mixtures of matrine/toosendanin mainly produced addition owing to their similar modes of action aiming at the nervous system. Combinations of celangulin mixed with matrine or toosendanin at 1:9 exhibited synergism, which is attributed to the interference of matrine or toosendanin with the detoxification enzymes of celangulin. Both the synergistic combinations were inappropriate for rotifer extermination in Isochrysis sp. cultivation owing to the high phytotoxicity resulting from the absence of cell walls. However, the celangulin/toosendanin (1:9) mixture decreased rotifer reproduction without damaging cells of Chlorella and Nannochloropsis sp. Application of frequent, low doses of celangulin/toosendanin (1:9) mixture also reduced the dosage of biocides, thereby reducing the cost of exterminating rotifers, and indicating a considerable practical application in microalgal cultivation.

Transcriptome sequencing and characterization for Kappaphycus alvarezii

The transcriptome of Kappaphycus alvarezii was 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 on de novo assembly. 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 of K. alvarezii provides a valuable resource for potential gene identification and comparative genomic studies.

Changes of photosynthetic performances in mature thalli of the red alga Gelidium amansii (Gelidiaceae) exposed to different salinities

ABSTRACT Photosynthetic parameters, including net O2 evolution, pigment content and fast chlorophyll a (Chl a) fluorescence kinetics, were studied in mature thalli of Gelidium amansii, a marine agar-producing red seaweed, exposed to different salinities (0–35 psu) for 10 days. The results showed that the net O2 evolution 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 Chl a, 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 O2 evolution 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 of G. amansii cultivation in estuarine waters with 20–32 psu salinity.

ENSO and eucheumatoid algae cultivation in China

The outbreaks of ice-ice disease and Epiphytic Filamentous Algae (EFA) on eucheumatoid algae have a close relationship with environmental factors. El Niño together with the corresponding atmospheric Southern Oscillation (ENSO) is the most influential natural climate pattern on Earth. The relationship between the outbreaks of ice-ice disease and EFA on eucheumatoid algae with ENSO was investigated from the perspective of environmental conditions in Lian Bay, Lingshui, China. The low salinity and high temperature during August to October were dangerous for the cultivation of eucheumatoid algae in Lian Bay, especially in La Niña years. The possibility of disease and EFA would be decreased if the algae were cultured in deeper water. We suggest that the algae be cultured in deeper water in the La Niña years in Lian Bay, Lingshui from August to October. Based on the results of this study, future research should pay more attention to the relationship between ENSO and exceptional events in fisheries and aquaculture. Such information will be essential for developing appropriate strategies to predict the timing of exceptional events and help control their impacts.

Effects of low temperature stress on the antioxidant system and photosynthetic apparatus of Kappaphycus alvarezii (Rhodophyta, Solieriaceae)

ABSTRACT 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.

Differences in photosynthetic behaviour of Kappaphycus alvarezii and Kappaphycus striatus during dehydration and rehydration

Abstract 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.