38 DNA Replication in Plants

Abstract

The subject of this chapter is chromosomal DNA replication in higher plants. The discussion purposely is limited to results obtained with plants. References to viruses, plasmids, organelles, yeast, and other types of cells are few. Most of the pioneering work and insight on chromosomal DNA replication is traceable to research done with these organisms, but a review of the work need not be repeated here. This chapter has four sections. The first covers the genomic diversity of higher plants; the second covers the replicon, its properties, its hierarchical organization, its relation to the S phase of the cell cycle, and its involvement in chromosomal DNA maturation. The third section discusses the replication of the ribosomal genes. At the end of the chapter is a summary that lists salient points known about chromosomal DNA replication in higher plants.

DIVERSITY: A FEATURE OF THE PLANT GENOME
A striking feature among higher plants is the difference in genome size. Measurements from more than 2000 species show that plant genomes vary at least 2500-fold and cover a range from 0.05 pg of DNA in Cardamine amara to 127.5 pg of DNA in Fritillaria assyricaca (Bennett and Smith 1976Bennett and Smith 1991; Bennett et al. 1982). The chromosome number of different species, likewise, varies widely. For example, Happlopappus gracilis has n = 2, whereas Senescio biserratus has n = 100. The plant kingdom also is populated with allopolyploids which are the products of hybridization between diploid species and which, at first glance, appear as normal diploids. The...