Rieseberg Loren H, Carter Ronald, Zona Scott
Rancho Santa Ana Botanic Garden, 1500 N. College Ave., Claremont, CA, 91711, USA.
Evolution. 1990 Sep;44(6):1498-1511. doi: 10.1111/j.1558-5646.1990.tb03841.x.
Enzyme electrophoresis and restriction-fragment analysis of chloroplast DNA (cpDNA) and nuclear ribosomal DNA (rDNA) were used to test the hypothesis that both Helianthus neglectus and H. paradoxus are stabilized hybrid derivatives of H. annuus and H. petiolaris. The four species are annuals, diploid outcrossers, and have the same chromosome number. Helianthus annuus and H. petiolaris had the same allele in highest frequency for 16 of the 18 isozyme loci examined and had different majority alleles for only 6-Pgd3 and Pgi2. The two species had divergent rDNAs that could be distinguished by seven diagnostic restriction site mutations and three length mutations, and their cpDNAs could be differentiated by three diagnostic restriction site mutations. The alleles observed in H. neglectus were not a combination of those observed in H. annuus and H. petiolaris. Although H. neglectus had only one unique allele, it possessed none of the three alleles specific to H. annuus. In contrast, it had four of the seven alleles specific to H. petiolaris. Furthermore, H. neglectus had the same rDNA type as H. petiolaris and had the same cpDNA as that found in two populations of H. petiolaris ssp. fallax. These data allowed us to speculate that H. neglectus may be a recent derivative of H. petiolaris ssp. fallax, rather than a stabilized hybrid derivative as originally proposed. In contrast, H. paradoxus combined the alleles of H. annuus and H. petiolaris and had no unique alleles. At Adh2, H. paradoxus was monomorphic for an allele found only in H. petiolaris ssp. fallax, whereas at 6-Pgd3 and Pgi2, it was monomorphic for high frequency H. annuus alleles. Furthermore, H. paradoxus combined the rDNA repeat types of both proposed parents and had the chloroplast genome of H. annuus. These data provide compelling evidence that H. paradoxus, in contrast to H. neglectus, was derived via hybridization.
利用叶绿体DNA（cpDNA）和核糖体DNA（rDNA）的酶电泳及限制性片段分析，来检验如下假设：野生向日葵（Helianthus neglectus）和奇异向日葵（H. paradoxus）均为向日葵（H. annuus）和叶柄向日葵（H. petiolaris）的稳定杂交衍生物。这四个物种均为一年生植物，二倍体异交植物，且染色体数目相同。在所检测的18个同工酶位点中，向日葵和叶柄向日葵在16个位点上具有频率最高的相同等位基因，仅在6 - Pgd3和Pgi2位点上具有不同的优势等位基因。这两个物种具有不同的rDNA，可通过7个诊断性限制性位点突变和3个长度突变加以区分，其cpDNA可通过3个诊断性限制性位点突变进行区分。在野生向日葵中观察到的等位基因并非向日葵和叶柄向日葵中所观察到的等位基因的组合。虽然野生向日葵仅具有一个独特的等位基因，但它并不拥有向日葵特有的三个等位基因中的任何一个。相反，它具有叶柄向日葵特有的七个等位基因中的四个。此外，野生向日葵与叶柄向日葵具有相同类型的rDNA，并且其cpDNA与在叶柄向日葵ssp. fallax的两个种群中发现的cpDNA相同。这些数据使我们推测，野生向日葵可能是叶柄向日葵ssp. fallax的近期衍生物，而非如最初所提出的那样是稳定的杂交衍生物。相比之下，奇异向日葵则组合了向日葵和叶柄向日葵的等位基因，且没有独特的等位基因。在Adh2位点，奇异向日葵对于仅在叶柄向日葵ssp. fallax中发现的一个等位基因呈单态性，而在6 - Pgd3和Pgi2位点，它对于向日葵的高频等位基因呈单态性。此外，奇异向日葵组合了两个假定亲本的rDNA重复类型，并拥有向日葵的叶绿体基因组。这些数据提供了令人信服的证据，表明与野生向日葵不同，奇异向日葵是通过杂交产生的。
