盐度对灰叶马尾藻排卵及幼孢子体早期发育的影响

Effects of salinity on egg release and early development of Sargassum cinereum(Fucales,Phaeophyta) germlings

通过离体组织培养, 观察了灰叶马尾藻Sargassum cinereum 卵细胞分裂过程, 并探讨盐度对其卵释放和幼孢子体发育的影响.结果表明, 在实验盐度范围（15‰~42‰）内, 灰叶马尾藻均能正常排卵, 其中盐度22‰~34‰时, 卵可集中快速放散, 而偏高或偏低盐度导致卵子释放延迟, 同时高盐（30‰~42‰）比低盐（15‰~26‰）处理的灰叶马尾藻释放更多卵子.卵从卵窝孔刚排出时为1 核卵, 在随后4h 内经核分裂形成8 核卵, 其中只有1 个子核可与精子核结合成为受精卵, 其他子核消失.受精卵的第一、二次分裂为横分裂, 而第三、四次为纵分裂, 4 次分裂历时4～5h, 之后分裂速度加快, 细胞数目迅速增多, 1d 内形成幼孢子体.第2d 以假根生长为主, 此后叶状部逐渐生长.盐度显著影响灰叶马尾藻幼孢子体早期发育, 当盐度22‰~38‰时假根生长正常, 偏高或偏低盐度均不利于假根生成和伸长, 其中高盐度对假根生长的抑制程度更强;叶状部生长的适宜盐度为26‰~38‰.综上所述, 灰叶马尾藻卵释放及幼孢子体早期发育的适宜盐度为26‰~34‰, 其中最适盐度为34‰.

Nuclear division of eggs and cell division of zygote of Sargassum cinereum were observed by tissue culturein vitro. The effects of various salinity values （15‰, 22‰, 26‰, 30‰, 34‰, 38‰, and 42‰） on egg release and earlydevelopment of S. cinereum germlings were studied under laboratory conditions. The results indicated that the algaleggs could be released normally in the salinity range studied. The eggs were released concentratedly and rapidly in thesalinity range of 22‰~34‰; however, at 15‰, 38‰, or 42‰, concentrated egg release was delayed. More eggs weredetected at salinity over 30‰ than below 26‰. A freshly released unfertilized egg from the nest hole had only onenucleus in the center, which was then divided into eight daughter nuclei within about 4 hours; finally only one combinedwith sperm nucleus, and changed into zygote with a large nucleus in the center. The first two cell divisions of zygotewere transverse, and the subsequent two were all longitudinal. Four to five hours after fertilization were needed for thefour cell division, then zygote cleavage was speeded up and cell number was increased rapidly, and finally amulticellular germling was formed within about 22 hours. The rhizoid grew prior to thallus in the next day, and thenthallus length increased gradually. Salinity significantly affected the early development of S. cinereum germlings.Rhizoid grew normally in salinity range of 22‰~38‰; however, higher or lower salinity inhibited its forming and elongation, and the inhibition action at 42‰ was stronger than that at 15%o. In addition, tile suitable salinity for growth was 26%0-38‰ for S. cinereum thallus. In conclusion, tile suitable salinity was 26‰-34‰, and tile optimal salinity was 34‰ for early development of S. cinereum germlings.