de Melo Natoniel Franklin, Guerra Marcelo
Embrapa Semi-Arido, C.P.23, 56302-970, Petrolina, Pernambuco, Brazil.
Ann Bot. 2003 Aug;92(2):309-16. doi: 10.1093/aob/mcg138.
Cytologically, the species of Passiflora with known chromosome number can be divided into four groups: (1) 2n = 12, 24, 36; (2) 2n = 24; (3) 2n = 18, 72; and (4) 2n = 20. The base chromosome number proposed for the genus is x = 6, with x = 9, x = 10 and x = 12 being considered secondary base numbers. In the present study, variability of 5S and 45S rDNA sites was investigated in 20 species of these four groups to check the reliability of this hypothesis. In the group with x = 6, five diploid species (2n = 12) exhibit two 5S rDNA sites and two (P. capsularis, P. morifolia and P. rubra) or four (P. misera 2x and P. tricuspis) 45S rDNA sites. The hexaploid cytotype of P. misera had 12 45S rDNA sites and six 5S rDNA. A tetraploid species, P. suberosa, had ten 45S rDNA sites and four 5S rDNA sites, both in the same chromosomes as the 45S rDNA sites. In the group with x = 9, P. actinia, P. amethystina, P. edmundoi, P. elegans, P. galbana, P. glandulosa and P. mucronata displayed six 45S rDNA sites, whereas P. alata, P. cincinnata, P. edulis f. flavicarpa, P. edulis var. roxo and P. laurifolia had four sites. In this group, all species were diploid (2n = 18) and had only two 5S rDNA sites. Passiflora foetida, the only species with 2n = 20, had six 45S rDNA sites and four 5S rDNA sites. The species with x = 12 (2n = 24), P. haematostigma and P. pentagona, showed four 45S rDNA sites and two 5S rDNA. In general, the number and location of 5S and 45S rDNA sites were consistent with the hypothesis of x = 6 as the probable ancestral genome for the genus, while the groups of species with x = 9, x = 10 and x = 12 were considered to be of tetraploid origin with descending dysploidy and gene silencing of some redundant gene sites, mainly those of 5S rDNA.
从细胞学角度来看，已知染色体数目的西番莲属物种可分为四组：（1）2n = 12、24、36；（2）2n = 24；（3）2n = 18、72；以及（4）2n = 20。该属的基本染色体数被认为是x = 6，而x = 9、x = 10和x = 12被视为次生基本染色体数。在本研究中，对这四组中的20个物种的5S和45S rDNA位点变异性进行了研究，以检验这一假设的可靠性。在x = 6的组中，五个二倍体物种（2n = 12）有两个5S rDNA位点，两个物种（金钟西番莲、多花山竹子叶西番莲和红西番莲）或四个物种（小花西番莲2x和三尖西番莲）有45S rDNA位点。小花西番莲的六倍体细胞型有12个45S rDNA位点和6个5S rDNA位点。四倍体物种苏贝罗西番莲有10个45S rDNA位点和4个5S rDNA位点，两者都位于与45S rDNA位点相同的染色体上。在x = 9的组中，紫花西番莲、紫水晶西番莲、埃德蒙多西番莲、秀丽西番莲、加布纳西番莲、腺叶西番莲和具刺西番莲有6个45S rDNA位点，而具翅西番莲、辛辛那提西番莲、黄果西番莲、紫果西番莲变种和月桂叶西番莲有4个位点。在这一组中所有物种都是二倍体（2n = 18），并且只有两个5S rDNA位点。西番莲，唯一2n = 20的物种，有6个45S rDNA位点和4个5S rDNA位点。x = 12（2n = 24）的物种，血柱头西番莲和五角西番莲，有4个45S rDNA位点和2个5S rDNA位点。总体而言，5S和45S rDNA位点的数量和位置与x = 6作为该属可能的祖先基因组这一假设一致，而x = 9、x = 10和x = 12的物种组被认为是四倍体起源，伴有染色体数减少和一些冗余基因位点（主要是5S rDNA位点）的基因沉默。
