Preliminary Study On Growth And Reproduction Of Attached Ulva Prolifera And Its Continuous Multi-generation Ploidy Ratio On Raft Frames From South Yellow Sea

Ulva prolifera belongs to Chlorophyceae,Ulvaceae,which is a species of eurythermal and euryhalinous macroalgae distributed in worldwide oceans.Its growth state is divided into floating and fixed.In recent years,whenever green tide erupting in Yellow Sea,its advantage species of floating U.prolifera grows very fast and has various ways of reproduction under particular circumstances,which has caused huge disasters of ocean environment.It is generally recognized that green tide U.prolifera has a life cycle pattern:isomorphic alternation of sporophyte and gametophyte generations.It has four modes of reproduction:sexual reproduction,asexual reproduction,parthenogenesis and vegetative reproduction.Meanwhile,unlike the short-lived outbreak of floating U.prolifera,U.prolifera which attached in the South Yellow Sea has perennially lived in shore reef of intertidal zone and Porphyra rafts of Subei shoal,and together with Blidingia sp.constituted the advantage species of green algae population.Due to the popularity of molecular identification and remote sensing monitoring techniques.many experts have speculated that the floating U.prolifera in the period of green tide erupting originated from the attached U.prolifera in the shoaly Porphyra rafts of the South Yellow Sea.Therefore,in order to better understand whether the same species exists biological difference in different geographical locations and growth states,it appears to be particularly important to study the growing development and life history of attached U.prolifera.In this study,four major reproductive breeding modes,which are the same as floating U.prolifera,were observed by long-term culture using attached U.prolifera as materials,and the process of each phase was described with corresponding diagrams.We used flow cytometry to measure DNA contents of generative cells released from different stages of U.prolifera,verifying the microscopic changes in the two critical phases in the metagenesis life history of U.prolifera:the sporophyte to gametophyte(diploid to haploid)and gametophyte to sporophyte(haploid to diploid)do occur.In the cultivation process of a large number of single thalli,we found a phenomenon that the attached U.prolifera in the wild often appeared to release two or more types of germ cells,so we purified and cultivated the parthenogenetic life history of the common species of attached green algae:U.prolifera and U.flexuosa.Through the amplification and sequencing of ITS and 18S rDNA sequences,found that each generation can stabilize heredity,the growing development ability of male gametophytes being weaker than female gametophytes,and decreased growing development ability with higher generations.Through separating the observed U.prolifera and U.flexuosa individuals of every phase of life history under laboratory conditions,we obtained the sporophyte and gametophyte purified from them.It was found that different types of generative cytocyst within the same species were different in cell size:gametangia was larger than sporangia in U.flexuosa and U.prolifera while the difference in cell area was not significant.There were also some difference in generative cell size:spores of the same strain>female gametes>male gametes,and the morphological boundaries of different types of generative cells of U.flexuosa were less obvious,the size difference was smaller than that of U.prolifera.The spores,female and male gametes of U.prolifera was more easily distinguished because of differences in cell size.The results of the study can be used to distinguish between sporophyte generations and gametophyte generations.In this experiment the effects of attachment and germination of generative cells on different material substrates were also studied.It was found that the attachment rate of U.prolifera spores was the highest in materials used in the Porphyra aquaculture rafts,followed by materials used in fishing-boats,while the attachment rate of other materials like cotton eloth was very low.In addition,the biomass of U.prolifera seedlings germinated on the material with higher attachment rate is not necessarily high.In this experiment,the biomass of seedlings germinated from different materials per unit area:wood pulp>filter paper>chemical fiber>cotton cloth.rubber and nylon rope>plastic.As a dominant source of green tide,the floating and attached Ulva population both have an alternation of isomorphic metagenesis:Life history of sporophyte and gametophyte circulation.Based on methods of conventional morphological classification and 18S rDNA sequence data among ribosomal RNA gene were widely used to classify relative species in Ulva spp.collected from six sites of Porphyra raft frames in the coast of South Yellow Sea over a period of>1.5 years,it was found that the Ulva population,which attached on the raft,was composed of Blidingia minima,U.prolifera,U.flexuosa,Ulva intestinalis and Ulva compressa.Among them,the perennial fixed species were dominated by U.prolifera and U.flexuosa.In the study,We also used traditional observing generative cell method and flow cytometry method to obtain the continuous changes in biphase and sex ratios of U.flexuosa and U.prolifera,and to assess their phase advantage with time and seasonal changing.It showed that the ploidy alternated quantitative superiority with seasonal changing:sporophyte are predominant mainly in winter and spring,and gametophyte mainly in summer and autumn.Meanwhile?the sex ratio of male and female gametophytes remained 1:1 throughout the year.Results also showed that quantity ratio of thalli in sporophyte generation and gametophyte generation was different in different sites within the same month though these raft areas being very close to each other,which indicated that there was phenomen of a continuous reproduction,multiple generations coexisting and growing continuously in these populations.This study provides evidence for explaining Jiangsu maritime space of attached green algae mainly in which ways for reproducing when the green tide erupted.It also provides a new idea for the cause of the large-scale outbreak of U.prolifera in this period.