Reis Aryane C, Sousa Saulo M, Vale Aline A, Pierre Patrícia M O, Franco Ana L, Campos José Marcello S, Vieira Roberto F, Viccini Lyderson F
Universidade Federal de Juiz de Fora, Departamento de Biologia/Laboratório de Genética 36036-900, Juiz de Fora, MG, Brazil.
Universidade Federal de Santa Catarina, Campus Universitário Curitibanos, Rodovia Ulisses Gaboardi-km 3 89520-000, Curitibanos, SC, Brazil.
Am J Bot. 2014 Jun 1;101(6):1002-1012. doi: 10.3732/ajb.1400149. Epub 2014 Jun 11.
• Premise of the study: Tropical regions have high species diversity, and polyploidization is a major mechanism of speciation in plants. However, few cases of natural polyploidy have been reported in tropical regions. Lippia alba, is a tropical, aromatic shrub with a wide distribution, extensive morphological plasticity, and several chemotypes. The species has long been recognized as a diploid with 2n = 30 chromosomes. Recently, two variations in chromosome number (2n = 60; 2n = 12-60) have been reported, suggesting the occurrence of polyploidy within the species.• Methods: Flow cytometry was used to investigate the genome size in 106 accessions from 14 Brazilian States. Conventional and molecular cytogenetic techniques and pollen viability analysis were employed to characterize each chromosome number observed.• Key results: The DNA 1C-value varied from 1.17 to 3.45 pg, showing a large variation in genome size. Five distinct chromosome numbers were observed (2n = 30, 38, 45, 60, 90); three are cytogenetically described here for the first time. The 5S rDNA signals varied proportionally according to each chromosome number, but 45S rDNA sites did not. High rates of meiotic irregularity were observed, mainly in cytotypes with higher chromosome numbers.• Conclusions: The data provide new support for the occurrence of a polyploid series in Lippia alba. We provide a hypothesis for how this complex may have arisen. Other cryptic polyploid complexes may remain undiscovered in tropical regions.
• 研究前提：热带地区物种多样性高，多倍体化是植物物种形成的主要机制。然而，热带地区自然多倍体的案例报道较少。 Lippia alba是一种热带芳香灌木，分布广泛，形态可塑性强，有多种化学型。该物种长期以来被认为是二倍体，有2n = 30条染色体。最近，有报道称其染色体数目出现了两种变异（2n = 60；2n = 12 - 60），表明该物种内存在多倍体现象。
• 方法：采用流式细胞术研究来自巴西14个州的106份种质的基因组大小。运用常规和分子细胞遗传学技术以及花粉活力分析来表征观察到的每种染色体数目。
• 主要结果：DNA 1C值在1.17至3.45 pg之间变化，表明基因组大小存在很大差异。观察到五个不同的染色体数目（2n = 30、38、45、60、90）；其中三个在此首次进行细胞遗传学描述。5S rDNA信号根据每个染色体数目成比例变化，但45S rDNA位点并非如此。观察到较高的减数分裂不规则率，主要出现在染色体数目较多的细胞类型中。
• 结论：这些数据为Lippia alba中多倍体系列的存在提供了新的支持。我们提出了一个关于这个复合体可能如何产生的假设。热带地区可能还有其他未被发现的隐性多倍体复合体。
