Ranunculus

The term apomixis encompasses a suite of processes whereby seeds form asexually in plants. In contrast to sexual reproduction, seedlings arising from apomixis retain the genotype of the maternal parent. The transfer of apomixis and its effective utilization in crop plants (where it is largely absent) has major advantages in agriculture. The hallmark components of apomixis include female gamete formation without meiosis (apomeiosis), fertilization-independent embryo development (parthenogenesis), and developmental adaptations to ensure functional endosperm formation. Understanding the molecular mechanisms underlying apomixis, a developmentally fascinating phenomenon in plants, is critical for the successful induction and utilization of apomixis in crop plants. This review draws together knowledge gained from analyzing ovule, embryo, and endosperm development in sexual and apomictic plants. It consolidates the view that apomixis and sexuality are closely interrelated developmental pathways where apomixis can be viewed as a deregulation of the sexual process in both time and space.

Genome size (DNA C-value) data are key biodiversity characters of fundamental significance used in a wide variety of biological fields. Since 1976, Bennett and colleagues have made scattered published and unpublished genome size data more widely accessible by assembling them into user-friendly compilations. Initially these were published as hard copy lists, but since 1997 they have also been made available electronically (see the Plant DNA C-values database http://www.kew.org/cval/homepage.html). Nevertheless, at the Second Plant Genome Size Meeting in 2003, Bennett noted that as many as 1000 DNA C-value estimates were still unpublished and hence unavailable. Scientists were strongly encouraged to communicate such unpublished data. The present work combines the databasing experience of the Kew-based authors with the unpublished C-values produced by Zonneveld to make a large body of valuable genome size data available to the scientific community. C-values for angiosperm species, selected primarily for their horticultural interest, were estimated by flow cytometry using the fluorochrome propidium iodide. The data were compiled into a table whose form is similar to previously published lists of DNA amounts by Bennett and colleagues. The present work contains C-values for 411 taxa including first values for 308 species not listed previously by Bennett and colleagues. Based on a recent estimate of the global published output of angiosperm DNA C-value data (i.e. 200 first C-value estimates per annum) the present work equals 1.5 years of average global published output; and constitutes over 12 % of the latest 5-year global target set by the Second Plant Genome Size Workshop (see http://www.kew.org/cval/workshopreport.html). Hopefully, the present example will encourage others to unveil further valuable data which otherwise may lie forever unpublished and unavailable for comparative analyses.