(American Journal of Botany. ;90:0.)
© Botanical Society of America, Inc.
Rapid rDNA evolution in tobacco
Skalick;aaa et al. address the interaction between allopolyploidy and rDNA evolution in tobacco (Nicotiana tabacum), which is thought to have formed up to six million years ago as a natural hybrid and polyploid derived from ancestors of the modern diploid species Nicotiana sylvestris and Nicotiana tomentosiformis. In nascent polyploids the sudden duplication of all genetic loci and their physical context coupled with the abrupt need to regulate the expression of divergent but homologous genes in a nucleus that is often meiotically chaotic has long been hypothesized to sponsor rapid sequence and chromosome structural changes. The authors' data provide evidence for these historical hypotheses.
(see p. 988)
Gaya et al. reconstruct the phylogeny of three widespread genera of typically yellow-orange lichens, the lichenized ascomycetes Fulgensia, Caloplaca, and Xanthoria. The position of these genera as well as their monophyly or polyphyly has been extensively debated in lichenological literature. One reviewer wrote about the paper that "its major strength, in addition to dealing with a problem of current interest, is the outstanding phylogenetic method. I particularly liked the separate analysis on ambiguous alignment (MP2), which was extremely interesting, even fun!"
(see p. 1095)
Recognizing the limitations to data collection in dune communities, Seliskar presents results from a well-designed investigation of the effects of grazing by feral horses, affectionately known as wild ponies, on the dune vegetation of Assateague Island, a dynamic mid-Atlantic Barrier Island, off the coast of Maryland, USA. As the horse population has increased since the 1960s, overgrazing and dune erosion have become problems. Employing fenced and unfenced plots on foredunes of four different morphologies, the author assessed grazing on two grass species, gathering useful information to aid managers balance herd size and vegetation.
(see p. 1038)
How the early growth environment in which plant cells grow influences subsequent developmental patterns is the subject of Jayasankar et al.'s study, in which somatic embryos derived from proembryogenic masses of Vitis vinifera anther and leaf tissue cultures placed in either liquid or solid media were compared by light and scanning electron microscopy. The liquid-culture-derived embryos (vs. solid-culture-derived embryos) have pronounced and persistent suspensors (vs. little or not visible), complex apical meristems (vs. rudimentary), and germinate rapidly (vs. dormant), leading the authors to speculate that the suspensor may be the production site for growth regulators responsible for enhanced development.
(see p. 973)
