Transcriptome Analysis and Physiological Responses of Economic Macroalga Gracilariopsis lemaneiformis under Sulfate Deficiency

Sulfur is an essential macronutrient for the growth of all photosynthetic organisms and plays important roles in different metabolic pathways.However,sulfur metabolism and its related research on macroalgae with important ecological value is rather limited.In this study,marine ecological valued macroalga Gracilariopsis lemaneiformis was used to study the general physiological responses and transcriptome profiling under the sulfate deficiency.The relative growth rate of algae under sulfate deficiency was statistically significantly lower than that of control after 6 days.However,no significant differences were observed in the pigments content and Fv/Fm value,indicating that the photosynthesis was not obviously affected under the sulfate deficiency.Furthermore,the significantly increased soluble protein and carbohydrate contents,and indistinctively differentially expressed sulfate transporter/permease(ST)and ATP sulfurylase(ATPS)genes suggesting that G.lemaneiformis cells did not use sulfur from internal protein and carbohydrate pools but utilize stored sulfur from vacuole to satisfy their nutritional requirements during the sulfate deficiency.Transcriptome data showed that most annotated differentially expressed genes(DEGs)were down-regulated under the sulfate deficiency,including a large proportion of genes involved in the pathway of sulfur metabolism.Therefore,it was concluded that the pathway of sulfur metabolism was suppressed under the sulfate deficiency in G.lemaneiformis.The results and analysis in this study provide a comprehensive understanding for the physiological and molecular response of G.lemaneiformis to sulfate deficiency.

Eff ects of temperature on photosynthetic performance and nitrate reductase activity in vivo assay in Gracilariopsis lemaneiformis (Rhodophyta)

Gracilariopsis lemaneiformis is an economically-valued species and widely cultured in China at present.After being acclimated to diff erent growth temperatures(15,20,25,and 30°C)for 7 days,the relative growth rate(RGR),nitrate reductase activity,soluble protein content and chlorophyll a fl uorescence of G.lemaneiformis were examined.Results show that RGR was markedly aff ected by temperature especially at 20°C at which G.lemaneiformis exhibited the highest eff ective quantum yield of PSII[Y(II)]and lightsaturated electron transport rate(ETR max),but the lowest non-photochemical quenching.Irrespective of growth temperature,the nitrate reductase activity increased with the incubation temperature from 15 to 30°C.In addition,the greatest nitrate reductase activity was found in the thalli grown at 20°C.The value of temperature coeffi cient Q10 of alga cultured in 15°C was the greatest among those of other temperatures tested.Results indicate that the optimum temperature for nitrate reductase synthesis was relatively lower than that for nitrate reductase activity,and the relationship among growth,photosynthesis,and nitrate reductase activity showed that the optimum temperature for activity of nitrate reductase in vivo assay should be the same to the optimal growth temperature.

The environmental adaptability and reproductive properties of invasive green alga Codium fragile from the Nan'ao Island,South China Sea

It has been widely recognized that biological invasion has become one of the greatest threats to the ecosystem.Codium fragile is an invasive species which exhibits a variety of attributes like parthenogenesis,winter fragment,and vegetative reproduction;and therefore,it has become a successful invader,colonizing most subtropical regions.In China’s southeast coastal aquaculture waters,the green algal bloom caused by C.fragile will probably become a serious problem.In order to understand more details about the species,an experiment focused on its reproductive characteristics was conducted using culture established from a sample collected in the aquaculture raft of the Nan’ao Island in the South China Sea.The results showed that there were two types of gametes resembling aplanospores and zoospores respectively,both of which were able to germinate.During the gametes liberation,a long mucilage tube was formed out of the mouth of the gametangium assisting dispersal of gametes away from the parent plant.This tube was adapted not only to its surrounding flowing water environment but also to its parent plant’s outer gelatinous structure.In general,the optimum temperature for gametes release and germination was 15-20℃ and 15℃,respectively,which corresponded to the local offshore marine water.The plant was observed to produce vegetative buds under favourable reproductive conditions which were called propagules.They were capable of developing into filamentous thalli.The results will provide some scientific evidences for revealing the biological mechanism of bloom and control strategies of invasive green algae.

Variation of Environmental Factors and Dominant Population Succession of Microalgae Planktonic in Closed Shrimp Pond

In order to investigate the influence of season changes of environmental factors in closed shrimp ponds on the community structure of planktonic microalgae,this paper conducted isolated tests to the temperature,pH,total nitrogen( TN),total phosphorus( TP) and chlorophyll a in the shrimp culture ponds,analyzed the planktonic microalgae community structure and changes of dominant species in water over the same period,with the aim to explain the responses of microalgae community to changes of environmental factors in the pond without foreign water sources.The results showed that pond water temperature and TP content gradually increased from April to the end of September and then declined in October; water pH first decreased and then increased; TN and chlorophyll a first increased and then decreased.The dominant species in the pond were Cyclotella sp.,Navicula sp.,Oocystis borgei and S.quadricauda in the early stage( Apirl-May),Chlamydomonas sp.,Chlorella sp.,S.quadricauda,Golenkinia radiata and Pseudanabeanain in medium stage( June-July),Microcystis,Pseudanabeana,Chlorella sp.And S.quadricaudain in the mid-late stage( August-September),Microcystis,Pseudanabeana,Oscillatoria sp.and Chlorella sp.in the late stage( October-December),and Chlorella sp.,Golenkinia radiate,S.quadricauda in the last stage.Diatoms and green algae were the dominant species in the early stage when the water had low temperature,low N and P nutrition but high N/P and a certain salinity.With the increase of temperature,water desalination and accumulation of N and P nutrition,algae became the dominant species.Cyanobacteria became the strong dominant stages in the mid-late stage when the water had high temperature in the state of eutrophication,and there were also some green algae which were fond of high temperature and had resistant to pollution.In the late stage,cyanobacteria were the absolute dominant stage,but with the decrease of water temperature in the last stage,green algae became the dominant species,and planktonic microalgae biomass in the pool decreased.