Basic And Applied Study On Reproduction Biology Of The Economic Seaweeds Sacharina Japonica, Undaria Pinnatifida And Sargassum Horneri

Sacharina japonica, Undaria pinnatifida and Sargassum horneri are three important economic seaweeds in China, study on the basic reproduction biology of the three species and document their reproduction characteristics can help us improve the breeding technology and solve the aquaculture problems.The thesis includes the evaluation of the sperm life-span of S. japoncia and U. pinnatifida, the life-cycle of monoecious gametophtyes of U. pinnatifida and the cryopreservation of zygotes of S. horneri.1)The potential life-span of the sperm of two seaweeds, S. japonica and U. pinnatifida, was first assessed by their ability to fertilize eggs. Results show that some sperm of S. japonica stored in dark at 12°C were able to fertilize eggs up to 12 h after discharge, while the sperm of U.pinnatifida can only survive 1 h in the dark at 18℃. Sperm-contamination was further confirmed in large-scale breeding of S.japonica based on microsatellites. According to the results, independent cultured system for parental-sporophytes was established to solve the mixture problem in the breeding company.2)The unusual zoospore-derived monoecious gametophytes of U.pinnatifida were first discovered. To understand this phenomenon, a comprehensive screening in previously identified male gametophyte cultures isolates was carried out. Forty-three percent of the isolates developed both antheridia and oogonia on the same filamentous fragment, suggesting that the phenomenon was common in the male gametophytes of the cultivars tested. Selfing of the monoecious gametophyte gave rise to morphologically normal sporophytic offspring. The selfed sporophytic offspring were grown to maturity in open sea cultivation. Active zoospores were released from mature sporophylls. The majority of these developed into male gametophytes, while 15–20% developed into the observed monoecious structures on the same filament. Using PCR amplification it was found that all the monoecious gametophyte isolates, the selfed sporophytic offspring and the F1 gametophytes derived from zoospores released by the selfed sporophytes lacked the female-linked microsatellite sequence(a part of the locus Up-AC-2A8, GenBank accession No. AY738602.1), indicating their male nature. Meanwhile, they also have the same genotypes at twenty SSR loci. With the new discovery of the male sporophyte obtained by selfing the monoecious gametophyte, in combination with the previous finding of the potential of parthenosporophyte to release female spores, crossing of the spores from these two lines of sporophytes was successfully applied to the seedling production. The finding of this investigation will pave a way of using pure sporophytic lines to cross for selecting offspring with expected agronomical features demanded by the farming industry in the future.3)The development of zygotes naturally dropping from the conceptacles of S. horneri were investigated after stored at 4°C for fixed time periods. The results showed that the zygotes mortalities conserved at 4 °C for 6 and 20 hours were the same as that of the zygotes preserved at 15°C. The zygotes cultured at 4°C for less than 20 hours showed no problem to attach and grow on the substratum. Discoveries of this investigation provided data support of transporting the zygotes over distance under low temperature for seedling production when necessary.