DNA Content -

Plant cells contain large amounts of DNA, the amount being very variable between species from the smallest (Arabidopsis thaliana, 0.5 picogram (pg) per haploid genome) to some members of Loranthaceae (with over 100 pg per haploid genome)

Even the smallest plant genome is about five times larger than that found in Drosophila melanogaster and contains much more DNA than is required to specify all the proteins synthesized during the course, of development.

Function of this additional DNA - By using renaturation kinetics analysis it has been possible to analyze various plant genomes for additional (repetitive) DNA. Analysis of renaturation kinetics relies on the fact that when double-stranded DNA is denatured into two single strands, then given a suitable temperature and ionic environment, the two strands will anneal again. The process occurs by random collision, so the role of reannealing depends on the initial concentrations of the different sequences present.

A distinguishing feature of many eukaryotic genomes is the presence of, large amounts of repetitive DNA. Most eukaryotic nuclear genomes contain between 10% and 80% repetitive DNA. A great deal of the repeated DNA in higher plant genomes exists in the form of "tandem arrays" in which a basic sequence is repeated serially many times to form a large block. Numerous repeated sequences are interspersed in many regions of the genome rather than concentrated in arrays at one or two sites

In the larger plant genomes, in which there are higher percentages of repetitive DNA, it is likely that interspersed repeat sequences will be found adjacent to other repeats at least as often as they are found next to single copy DNA. It is sometimes possible to distinguish families of moderately repetitive and highly repetitive sequences. Highly repetitive DNA is often found at centromeres in a condensed form known as heterochromatin.