坛紫菜减数分裂位置的杂交试验分析

Cross experiments and analysis of the position of meiosis in Porphyra haitanensis (Rhodophyta)

利用坛紫菜人工色素突变体与野生型进行杂交试验,通过观察F1叶状体中是否出现颜色分离和颜色嵌合体来证明坛紫菜减数分裂发生的确切位置。以红色型人工色素突变体(SPY1和R10)作为母本,其特征:叶状体呈红色或桔红色,藻体薄而弹性差,无边缘刺;以野生型(wt)作为父本,其特征:叶状体呈棕绿色,藻体厚而富有弹性,有丰富的边缘刺。在杂交组SPY1(♀)×wt(♂)和R10(♀)×wt(♂))的F1叶状体中,均出现了2种亲本色和2种新颜色,它们分别为红色(R,母本色),野生色(W,父本色),浅红色(R′,比R色稍浅)和似野生色(W′,比野生色稍红)。4种颜色在F1叶状体上,出现了分离并形成了呈直线型排列的不同色块,从而产生了大量由2～4个色块组成的颜色嵌合体;单个嵌合体上的色块数最多为4块。在颜色嵌合体中,R和R′2种色块的藻体薄而弹性差,无边缘小刺,而W和W′2种色块的藻体厚而弹性好,富有边缘刺。在F1叶状体中,颜色嵌合体占95.2%～96.7%,单色叶状体只占3.3%～4.8%。上述结果说明,坛紫菜杂合丝状体产生的壳孢子,其萌发时进行的最初两次细胞分裂是减数分裂,它所产生的4个子细胞继续分裂,最终发育成含2～4个色块组成的颜色嵌合体;2种新颜色是由于在减数分裂的第一次分裂时发生了染色体交换和重组所产生的。本文使用的两个色素突变体,除含2个或2个以上的颜色变异基因外,还含有分别与藻体厚薄和边缘刺出现相关的变异基因,并且它们与颜色变异基因是连锁的。F1颜色嵌合体中的重组色块在3种主要光合色素和色素蛋白的含量、生长速度和成熟早晚等方面均表现出比亲本色块更好的特性,暗示利用色素突变体杂交方法有可能培育出坛紫菜的优良品系。

Cross experiments between the artificial pigmentation mutants and the wild type in Porphyra haianensis Chang et Zheng, were＂ carried out to examine the occurrence of meiosis in its life history, according to the appearance of color segregation and colorsectored blades in the F1 gametophytic blades developed from the conchospors of the heterozygous conchocelis. Two red types of pigmentation mutants （ SPY- 1 and R-10） were used as female parent, and their blades show red or red orange in color, thin and weak elasticity and have no denticles on their marginal parts. The wild type （wt） was used as male parent, and its blades show wild-type color, thick and good elasticity and have many marginal denticles. Among the Fl gametophytic blades from the crosses of SPY- 1 （ ♀ ） × wt（♂） and R - （ ♀ ） × wt（♂）, two parental colors （R and W） and two new colors （R＇, fighter in color than R; W＇, wild- type-like color and redder than W） appeared. Linear segregation of colors occurred in the blades, and therefore, the color-sectored blades with 2 - 4 sectors were formed. In the color-sectored blades, the sectors of R and R＇ were thinner than sectors of W and W＇, showing weak elasticity and without marginal denticles. However, the sectors of W and W＇ were thick, showing good elasticity with many marginal denticles. 95.2% -96.7% of the F1 gametophytic blades were color-sectored blades, and only 3.3% -4.8% of them were single-colored blades. These results indicated that the meiosis of P. haitanensis occurs during the first two cell divisions of the germinating conchospore, and thus it was considered that the initial four cells of the developing sporeling constitute a linear genetic tetrad leading to the formation of the color-sectored blades. The new colors of R＇ and W＇ were recombinant colors because the occurrence of chromosome recombination during the first cell division of the meiosis. It was certain that the color phenotypes of two mutants used in this paper resulted from two or more mutations in different genes, and that they also have mutations relative to blade thickness and formation of the marginal denticles, which is linked with color mutations. The recombinant colors of R＇ and W＇ were better in contents of chlorophyll a （ Chl. α ）, phycoerythrin （PE） and phycocyanin （PC）, and growth and maturation, indicating that the improved varieties probably could be obtained through crosses between the pigmentation mutants or between the pigmentation mutant and the wild type in P. haitanensis.