Molecular phylogeny and chromosome evolution among the creeping herbaceous Oxalis species of sections Corniculatae and Ripariae (Oxalidaceae).

Oxalis sections Corniculatae DC. and Ripariae Lourteig are composed mainly of creeping herbs. They not only share strong morphological similarities, such as the presence of a reptant stem but also some cytogenetic characteristics. Several species in section Corniculatae share a base chromosome number x=5 with species in section Ripariae, while other species in the former have a x=6. We used a molecular and cytogenetic approach to determine the phylogenetic relationships, test the previous taxonomic classification and study the genome rearrangements that led to the differences in chromosome size and basic chromosome number between both sections. Phylogenetic relationships were inferred based on DNA sequences from chloroplast and nuclear ribosomal ITS. The molecular phylogenetic analyses found that neither of the sections are monophyletic, but do support two clades. The first group contains diploid species with x=5, large chromosomes and high DNA content and the second diploid and polyploidy species with x=6, small chromosomes and low DNA content. The x=5 clade comprises species of both sections, while the x=6 clade was formed mainly by section Corniculatae species and O. serpens from section Ripariae. Our results suggest that x=5 and high DNA content are derived conditions, which may have resulted from descendent disploidy and proliferation of transposable elements. Thus, cytogenetic data superimposed on the phylogeny have shown two different modes of chromosome evolution in both lineages: (1) chromosome rearrangements and increase in genome size in the x=5 lineage and (2) polyploidy playing the main role in chromosome evolution among species in the x=6 species. A taxonomic revision for the two sections is suggested.

A model of bulb evolution in the eudicot genus Oxalis (Oxalidaceae).

The origins and monophyly of the bulbous habit in the eudicot genus Oxalis are uncertain, but key character state transitions in the evolution of true bulbs are currently thought to be reflected in extant pseudobulbous and other geophytic taxa. We test the relationships between the two major groups of bulbous Oxalis taxa, namely the southern African lineage which is centered in the speciose Cape Floristic Region (CFR), and the New World section Ionoxalis, by including the rhizomatous geophyte Oxalis acetosella, the caudiciform stem succulent Oxalis articulata, and the rhizomiform pseudobulbous Oxalis triangularis, in combined phylogenetic analyses of nrITS and trnL-F sequence data. We optimize several key bulbous characters in ancestral state reconstructions on produced phylogenies. Results of our analyses indicate that the evolution of bulbous characters in the genus is more complex than previously thought. Although the two major bulb types are homologous, the rhizomiform pseudobulbous habit arises from within true bulbs, and in most reconstructions the caudiciform stem succulent O. articulata is inferred to have secondarily lost several distinctive bulbous characters. O. acetosella is not as closely related to the bulbous lineage as previously thought. More sampling from other key taxa are needed before the order in which key bulbous characters were acquired can be verified. We discuss these results in terms of the taxonomic and ecological implications for the CFR Oxalis taxa.

Chloroplast-expressed glutamine synthetase (ncpGS): potential utility for phylogenetic studies with an example from Oxalis (Oxalidaceae).

Chloroplast-expressed glutamine synthetase (ncpGS), a nuclear-encoded gene containing several introns, is introduced as a tool for phylogenetic studies at lower taxonomic levels. This gene is a member of a multigene family, but it diverged long ago from the cytosolic-expressed members of the family and appears to be single copy in the majority of taxa examined to date. The conservation of both coding sequence and position of introns has allowed the design of primers for use in a broad range of dicot taxa to amplify and sequence a region of ncpGS that contains four introns. The utility of this region in phylogenetic studies of congeneric species is illustrated by an example using eight Oxalis species. The four introns in these taxa are typical in size (76 to 136 bp), base composition (high T content), and structure (e.g., sequence of splice sites and putative branch points) for plant internal introns. Levels of variation among these ncpGS sequences compare favorably with those of the internal transcribed spacer of nuclear ribosomal DNA (ITS) from the same taxa, and results of phylogenetic analysis of ncpGS data are generally congruent with previous results using ITS.

Origins of domestication and polyploidy in oca (Oxalis tuberosa : Oxalidaceae): nrDNA ITS data.

As part of a study aimed at elucidating the origins of the octoploid tuber crop "oca," Oxalis tuberosa, DNA sequences of the internal trancribed spacer of nuclear ribosomal DNA (nrDNA ITS) were determined for oca and several wild Oxalis species, mostly from Bolivia. Phylogenetic analysis of these data supports a group of these species as being close relatives of oca, in agreement with morphology and cytology, but at odds with traditional infrageneric taxonomy. Variation in ITS sequences within this group is quite low (0-7 substitutions in the entire ITS region), contrasting with the highly divergent (unalignable in some cases) sequences within the genus overall. Some groups of morphologically differentiated species were found to have identical sequences, notably a group that includes oca, wild populations of Oxalis that bear small tubers, and several other clearly distinct species. The presence of a second, minor sequence type in at least some oca accessions suggests a possible contribution from a second genome donor, also from within this same species group. ITS data lack sufficient variation to elucidate the origins of oca precisely, but have identified a pool of candidate species and so can be used as a tool to screen yet unsampled species for possible progenitors.

The endogenous gibberellins of vegetative and reproductive tissue of G2 peas.

The gibberellins (GAs) of both vegetative (leaves and stems) and reproductive (pods and seeds) tissue of the G2 strain of peas Pisum sativum L. were characterized in purified extracts by a combination of sequential silicic-acid partition column chromatography, and gas chromatography-mass spectrometry. Gibberellins A19, A20, A29 and an A29 catabolite were identified in both types of tissue. Gibberellins A9, A17 and A44 were also found in pods and seeds.