Goff L J, Coleman A W
J Cell Biol. 1987 Mar;104(3):739-48. doi: 10.1083/jcb.104.3.739.
Cells with polyploid nuclei are generally larger than cells of the same organism or species with nonpolyploid nuclei. However, no such change of cell size with ploidy level is observed in those red algae which alternate isomorphic haploid with diploid generations. The results of this investigation reveal the explanation. Nuclear DNA content and other parameters were measured in cells of the filamentous red alga Griffithsia pacifica. Nuclei of the diploid generation contain twice the DNA content of those of the haploid generation. However, all cells except newly formed reproductive cells are multinucleate. The nuclei are arranged in a nearly perfect hexagonal array just beneath the cell surface. When homologous cells of the two generations are compared, although the cell size is nearly identical, each nucleus of the diploid cell is surrounded by a region of cytoplasm (a "domain") nearly twice that surrounding a haploid nucleus. Cytoplasmic domains associated with a diploid nucleus contain twice the number of plastids, and consequently twice the amount of plastid DNA, than is associated with the domain of a haploid nucleus. Thus, doubling of ploidy is reflected in doubling of the size and organelle content of the domain associated with each nucleus. However, cell size does not differ between homologous cells of the two generations, because total nuclear DNA (sum of the DNA in all nuclei in a cell) per cell does not differ. This is the solution to the cytological paradox of isomorphy.
具有多倍体细胞核的细胞通常比同一生物体或物种中具有非多倍体细胞核的细胞大。然而，在那些单倍体和二倍体世代交替出现同形的红藻中，并未观察到细胞大小随倍性水平发生这样的变化。本研究结果揭示了其中的原因。对丝状红藻太平洋格氏藻的细胞进行了核DNA含量及其他参数的测量。二倍体世代的细胞核DNA含量是单倍体世代细胞核的两倍。然而，除新形成的生殖细胞外，所有细胞都是多核的。细胞核排列在细胞表面下方近乎完美的六边形阵列中。当比较这两个世代的同源细胞时，尽管细胞大小几乎相同，但二倍体细胞的每个细胞核周围的细胞质区域（一个“结构域”）几乎是单倍体细胞核周围细胞质区域的两倍。与二倍体细胞核相关的细胞质结构域所含质体数量是与单倍体细胞核相关结构域的两倍，因此质体DNA含量也是两倍。因此，倍性加倍反映在与每个细胞核相关的结构域大小和细胞器含量的加倍上。然而，这两个世代的同源细胞之间细胞大小并无差异，因为每个细胞的总核DNA（一个细胞中所有细胞核内DNA的总和）没有差异。这就是同形性细胞学悖论的答案。
