Ulva prolifera , a type of marine macroalgae, is the causative species behind green tides mainly in the Yellow Sea and adjacent regions. Nevertheless, it can be used as food or animal feed in South China. The vegetative fragments of U . prolifera are an important seed source for successive green tide blooms. Fragmentation shortens the transition time from the vegetative state to the reproductive state. However, the translation of the algal metabolites during gametogenesis is far from well understood. In this study, the dynamic metabolic profiles of U . prolifera thallus during fragmentation-induced proliferation were investigated using non-targeted metabolomics approach via a series of time course experiments in June 2017. After a 30 min low temperature shock, fragmentation induced a reproductive response of 91.57% of U . prolifera in 48 h, whereas the value was only 21.43% in the control group. A total of 156 chromatographic peaks were detected, and 63 metabolites were significantly changed in U . prolifera during reproduction. Aanlysis of the kinetic metabolic pattern showed that the fragments not only induced the formation of sporangia, but also led to complex metabolite accumulation. During fragmentation-induced proliferation, U . prolifera consumed different sugars at different time points. γ-Aminobutyric acid (GABA), glutamic acid, gallic acid, and malic acid may play important roles in germ cell formation and in the release of U . prolifera , whereas n-hexanol, 2-methyl-3-phenylindole, and 3-indoleacetonitrile may be beneficial for biotic stress resistance. Compared with the control group, in the treatment group, metabolites such as alcohols and organic acids also showed significant difference with the photoperiod at the initial stage of proliferation (before 60 h). In conclusion, changes in the levels of metabolites, including sugars, organic acids, and alcohol with photoperiod may be the strategy adopted by U . prolifera to cope with fragmentation in nature.

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Apical necrosis is a widely distributed disease in the culture of the marine agar-producing alga, Gracilariopsis lemaneiformis. In this study, 16 strains of epiphytic bacteria were isolated from the tip bleaching parts of G. lemaneiformis; of the 16 strains, two strains could induce healthy algal tips to become necrotic. They were identified as Thalassospira sp. and Vibrio parahaemolyticus by 16S rDNA sequence analysis and biochemical characterization. Using solid phase microextraction and gas chromatographymass spectrometry, the variation of volatile metabolites of G. lemaneiformis infected by these two strains of pathogenic bacteria was analyzed. The results showed that E-2-nonenal and 1-octen-3-one differed very significantly (P<0.01) between the Thalassospira infected group and the control group, while trichloromethane, 3-methyl butanal, benzaldehyde, and E-2-decenal differed significantly (P<0.05). The difference of 1-octen-3-one, benzaldehyde, and E-2-nonenal between the V. parahaemolyticus infected group and the control group was very significant (P<0.01), while 3-methyl butanal and octanal were significantly different (P<0.05). In conclusion, 1-octen-3-one, E-2-nonenal, and benzaldehyde might be the characteristic metabolites for the pathogenic infection and could be used as biomarkers for the disease prevention of G. lemaneiformis.

ABSTRACT. The seaweed Sargassum horneri is an important brown alga in the marine environment, and it is an important raw material in the alginate industry. Unfortunately, the fixed resource that was originally reported is now reduced or disappeared, and increased floating populations have been reported in recent years. We sampled a floating population and 4 fixed cultivated populations of S. horneri along the coast of Zhejiang, China. Inter-simple sequence repeat (ISSR) markers were applied in this research to analyze the genetic variation between floating populations and fixed cultivated populations of S. horneri. In total, 220 loci were amplified with 23 ISSR primers. The percentage of polymorphic loci within each population ranged from 53.64 to 95.45%. The highest diversity was observed in population 3, which was the local species that was suspension cultured in the lab and then fixed cultivated in the Nanji Islands before sampling. The lowest diversity was obtained in the floating population 4. The genetic distances among 620 J.R. Ren et al. ©FUNPEC-RP www.funpecrp.com.br Genetics and Molecular Research 14 (1): 619-625 (2015) the 5 S. horneri populations ranged from 0.0819 to 0.2889, and the distance tendency confirmed the genetic diversity. The results suggest that the floating population had the lowest genetic diversity and could not be joined into the cluster branch of the fixed cultivated populations.