Karyological observation on Saccharina japonica chromosomes stained with DAPI

Saccharina japonica (Aresch.)C.E.Lane,C.Mayes et G.W.Saunders(=Laminaria japonica Aresch.)(Phaeophyta)is an important economic seaweed in China.There is a distinct outcome about the chromosome number in this kelp due to the tiny size of these chromosomes.The karyotypes and chromosomes of S.japonica were observed after a series of treatments including pretreatment with 0.2% colchicines for about 10 h,Carnoy’s fixative,and mixture of enzymes prior to dropping from 30 cm height overhead glass slides for spreading the surface coat.The prepared chromosomes were stained with 4′,6-diamidino-2-phenylindole(DAPI), a fluorescent probe sensitive and specific to DNA.The chromosome numbers of the haploid male and female gametophytes were 31, respectively,and there were 62 in diploid sporophytes.Most of the chromosomes were either droplet or short bacilliform.In the meantime,the female gametophyte chromosomes were between 0.78 μm and 2.61 μm in size,larger than the males that were between 0.57 μm and 2.17 μm.Based upon the relative size of chromosome,the karyotypes of the female or male gametophyte chromosomes were primarily analyzed.All the results laid a solid foundation for a basic technique for localization of molecular markers on kelp chromosomes.