No abstract

A preliminary analysis of the sequence alignment of the chloroplast intergene atpβ-rbcL in tribe Valerianeae reveals that insertion-deletion evolutionary events ('indels'), combined with nucleotide substitutions, have occurred in large zones in some of the studied taxa. Due to the frequent occurrence and large size of indels within this tribe, intergene length varies from 531 to 788 base pairs within the studied species. This situation poses gap coding problems that we had to tackle before phylogenetic analysis. Four methods of gap coding were used: elimination of gapped sites ('complete omission'), 'missing data', 'fifth base' and Barriel's coding method, which translates indels into new multistate characters in the data matrix. After application of these four methods of data treatment, phylogenetic analyses (maximum parsimony) did not lead to very different results. Three robust clades emerged in each case, corresponding to the Centranthinae subtribe (genus Centranthus), the Fediinae subtribe (genera Fedia and Valerianella), and the American species of Valeriana. The theoretical basis and biological significance of these four methods are discussed in order to apply the best ones in future studies. To cite this article: M.B.

Pollen morphology and exine structure of the seven Hymenocallis Salisb. species present in Venezuela were investigated using scanning (SEM) and transmission (TEM) electron microscopy. Pollen grains of all species are monosulcate, heteropolar, with bilateral symmetry, oblate to peroblate, heterobrochate, semitectate-columellate, possess unequal tectal surfaces, and are clavate or baculate when viewed with TEM. They present two equatorial apexes. When observed under SEM their surfaces appear as granulate; however, it is evident from TEM that they are in fact constituted by pila. All the species possess very large pollen (ranging from 64 to 85 lm and from 125 to 155 lm for polar and equatorial axes, respectively), and no relationship was evident between pollen size and chromosome number. All the taxa are also very similar in relation to their pollen outline, ornamentation and internal structure, thus indicating that the genus is accurately delimited from the palynological point of view and that discrete characteristics can only be used in some cases to delimit individual species.

Nucleolar organizing region of eight species of Aloe was analyzed in somatic metaphases and interphase nuclei. All species showed a uniform 2n=14, with eight large chromosomes and six small chromosomes. Satellites were observed on the long arm of one or two pairs of large chromosomes and/or on the short arm of one of the small pairs. The silver-stained nucleolus organizing regions were located on the subtelomeric region of the long arm of one or two pairs of large chromosomes, except for Aloe dichotoma and Aloe maculata, which the AgNORs were located at a short arm of one of their small chromosomes. In most studied species, the active AgNOR number was four. However, this number changing from one to eight. For all species, the interphase number of nucleoli can be one or two, while, in Aloe excelsa, this number can be changing from one to eight. Polymorphism of active AgNORs and the number of interphase nucleoli were revealed, except for Aloe petricola, which active AgNORs were located only in the subtelomeric regions at the long arm of one of the L2 chromosomes, as well as in the L4 pair, which is agrément with the maximum number (three) of interphase nucleoli.

Summary Cytogenetic traits were examined in Aloe saponaria (2S), A. vera (2V and 4V), and the experimental diploid (VS) and triploid (VVS) hybrids. Karyotype 2nϭ2xϭ14 (8Lϩ6S) was confirmed in 2S and 2V, whereas 2nϭ4xϭ28 (16Lϩ12S) was ascribed to 4V. VS showed the expected karyotype 2nϭ2xϭ14 (8Lϩ6S), with slight differences between the long (L) homologues. VVS also showed the expected karyotype 2nϭ3xϭ21 (12Lϩ9S); however, several chromosome deviations reflecting the absence or addition of small (S) chromosomes, terminal deletions of variable size which led to the formation of atypical chromosomes, or the loss of a L chromosome were also observed. The implication of these karyological variations is discussed.