Phyllotactic Patterns: A Biophysical Mechanism for their Origin

The patterns seen in plant shoots and flowers, ‘phyllotaxis’,originate in an annular region. They are typically propagatedinward from this ring-like area. We show here that an initialundulating periodic pattern (a ‘whorl’ of hump-likeorgans) can arise in a flat unstructured annulus. The patternarises not from pre-localized pushes from below, but ratheras a spontaneous physical response of the expanding surfaceto lateral constraint. Physical properties of a uniform formativelayer (tunica) and a uniform substratum (corpus) provide thewavelength of the undulation and hence the number of organs.Establishment of the parameters for this buckling, as well asthe follow-through of organ development, is biological. We propose,however, that at the moment of periodic pattern initiation theplant tissue simply manifests the spontaneous but complex propertiesof a two-layered inanimate sheet. Phyllotaxis; tunica; corpus; patterning; shoot apex; morphogenesis; biophysics; buckling     

Low Genotyping Error Rates and Noninvasive Sampling in Bighorn Sheep

Abstract Noninvasive DNA sampling allows studies of natural populations without disturbing the target animals. Unfortunately, high genotyping error rates often make noninvasive studies difficult. We report low error rates (0.0–7.5%/locus) when genotyping 18 microsatellite loci in only 4 multiplex polymerase chain reaction amplifications using fecal DNA from bighorn sheep (Ovis canadensis). The average locus-specific error rates varied significantly between the 2 populations (0.13% vs. 1.6%; P < 0.001), as did multi-locus genotype error rates (2.3% vs. 14.1%; P < 0.007). This illustrates the importance of quantifying error rates in each study population (and for each season and sample preservation method) before initiating a noninvasive study. Our error rates are among the lowest reported for fecal samples collected noninvasively in the field. This and other recent studies suggest that noninvasive fecal samples can be used in species with pellet-form feces for nearly any study (e.g., of population structure, gene flow, dispersal, parentage, and even genome-wide studies to detect local adaptation) that previously required high-quality blood or tissue samples.     

Transgenic Grapevines: Regeneration of Shoots Expressing {beta}-Glucuronidase

Genetic transformation has been studied in fragmented shootapex cultures of Vitis vinifera L. following co-cultivationwith Agrobacterium tumefaciens. Transgenic shoots of the cultivarCabernet Sauvignon, tolerant to low levels of kanamycin, havebeen produced. Proliferation of transgenic cells in the presumptivebud forming area of cultured fragments has been observed usingthe enzyme activity of ß-glucuronidase (GUS) as amarker. The distribution of GUS stained cells both in this tissueand in transgenic shoots, the presence of low copy numbers ofthe neomycin phosphotransferase II gene in transgenic shootsand the relatively low levels of kanamycin resistance suggestthat these shoots contain both transformed and untransformedcells. Key words: Grapevine, transformation, Agrobacterium, GUS, NPTII