| Macroalgae of Phaeophyta plays an important role as the frame of seaweed flora.The genus Sargassum (Sargassaceae, Fucales) is the largest genus in the Phaeophytaand constituting an important part of the marine flora along the Chinese and Japanesecoast, which has extremely important ecological value. Sargassum horneri（Turn.）C. Agard as the species only found in Western North Pacific Ocean and Sargassumvachellianum Greville native to China are both the significant members in the subtidalseaweed flora along the coasts of the Eastern China Sea. The marine environment hasbeen damaged severely recent years by many kinds of human activity. There has beenevidence showing the seaweed flora, especially in shore, which began to deteriorateextensively. For the purpose of restoring the flora by artificial breeding, correlationtechniques have been paid increasing attention to.In order to establish technique of the two seaweeds’ artificial seeding, it wasobserved in this paper that maturation of the alga, release of eggs, embryology ofzygotes, development and growth of the germlings, and the effect of cultureconditions on germlings growth by culture in the lab. Additionally, the developmentof mature receptacles in Sargassum horneri was also completed under controlconditions indoor during culture.The results of culturing Sargassum vachellianum Greville showed thatreceptacles matured and released eggs and sperms at21℃-24℃under60to90μmolphotons·m-2·s-1and long-day (14L:10D) after cultured for1-5days. The fertilized eggswould immediately fall without attaching onto the surface of the receptacles andbegan to germination. Eight nuclei in the fresh released zygote would soon beginfusion to form a larger central nucleus before the first division. The zygote firstly underwent twice horizontal divisions and produced a small cell called as “rhizoidoriginal cell” that finally formed rhizoids after several divisions. The other three cellsof the divided zygote continued to divide and consist of the body of the germlings likelandmine, which could attach on the bottom of the flask after24hours of culture. Thefirst leaflets of Sargassum vachellianum shaped, and the second one appeared aprotuberance at the basal part of the first after cultured for15days. There were6to7leaflets whose edge was waving after the culture of45days. The rule of leafletsformation in Sargassum vachellianum summarized that the new one appeared aprotuberance at the axillae of the old leaflet, and then broadened along the shorter axisfollowing elongation along the longer axis.The margin of leaflets had changed intosmooth-edged after cultured for50days. This kind of leaflets with entire marginsgrew quickly. The rudiments of lateral branches had been visible in the center of thejuvenile sporophyte around100days. Then the lateral branches increased rapidly, andthe number of leaflets on buranchlets increased in good time.The growth and development of the juvenile sporophytes (under age of20days)were significantly influenced by the culture temperature and light irradiance, showingfaster growth at21℃under40μmol photons·m-2·s-1. However, if the age of thegermlings was older than30days, they grew better at24℃under60μmolphotons·m-2·s-1. Before the formation of lateral branches the optimal light regime islong-day (14L:10D), instead of short-day(10L:14D) after the appearance of lateralbranches.In the investigation of culturing Sargassum horneri, it was found that the eggsadhered to the surface of female receptacles, and were released in turn from basal andmiddle partof the receptacles. The egg released newly had8nuclei which changedinto one large nucleolus after fertilization. The first division of zygote was transverseacross the longer axis of cell located at the nuclear plate, dividing zygote into atwo-cell juvenile sporophyte. The second cell division was transverse near theterminal part of one cell, dividing the cell into larger and smaller parts. Due to thesmaller cell would gradually develop into rhizoids which we named the ancestor cellof rhizoids. It took about48hours from the zygotes to multicellular germlings withrhizoids through subsequent cell divisions. The germlings length of Sargassumhorneri increased to more than3mm in average and grew2leaflets within15daysand then they developed5to6leaflets after30days. The rule of leaflets formation inSargassum horneri summarized that the new one appeared a protuberance at the axillae of the old leaflet, and then broadened along the shorter axis followingelongation along the longer axis.The length and number of germlings had increased in culture of35to75days,and the edge of a leaf had changed largely: from waving to toothed, then plumoseleaflet. The leafstalk appeared remarkable with prolonged culture period. The primarybranch increased visibly during80to120days, especially, on which the rudiments oflateral branches had been visible around100days. There were two patterns ofsporophytes during the culture from130to170days: the one had shorter primarybranch from whose basal to apical part the lateral branches developed quickly, theother one had even longer primary branch but the lateral branches developed quiteslowly, just keeping rudiments. The air-visicle occurred at axillae of leaflets on lateralbranches after culturing210days, and the male and female receptacles appeared after240days.Additionally, the growth and leaflets had been enhanced before the formation ofprimary laterals at the optimal condition:24℃,40μmol photons·m-2·s-1and long-day(14L:10D) during the cultivation of early germlings. Differently, after the formationof primary laterals, the growth of sporophytes and primary laterals had been enhancedat the optimal the condition:18℃,60μmol photons·m-2·s-1and short-day (10L:14D).In brief, the life circle of Sargassum horneri by artificial seedling indoor hadbeen completed. The fusion of eggs and sperm and the culture of juvenile sporophytesin Sargassum vachellianum under control conditions by artificial means had also beenachieved. |
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