Off the top of my head it's around 70 I think - all carbon-based life on the planet shares that much.

Hmm. I tried Science (http://www.sciencemag.org/cgi/search?src=hw&site_area=sci&fulltext=humans+and+plants%2C+dna%2C+percent), and can't help thinking I could find the answer there, if only I asked the question correctly. It could be that the archives of a botany journal or a journal of plant genetics would be more helpful, though.

A lot of it depends on how one does the calculation. For instance, humans and other primates all use the same base pairs. I don't recall seeing mitochondrial and nuclear DNA lumped in together.

That sounds fascinating. Would that I knew where to start!

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Googling again: plant genetics + human + DNA (http://www.google.com/search?hl=en&q=plant+genetics%2C+human%2C+DNA)
yields a number of very dense but promising resources.

This, for instance (http://www.thetech.org/genetics/ask.php?id=83) (lighter than most): Below is a table with genome size (number of base pairs), number of chromosomes, and number of genes for several species. As you can see, there is almost no connection between the size of the genome and the complexity of a plant or animal.

Species / Number of Chromosomes / Number of Genes / Size of Genome (million base pairs)
Human 46 ~25,000 3,300
Chicken 78 ~23,000 1,000
Fruit Fly 8 ~14,000 165
Butterfly ~380 unknown 124,900
Wall cress 10 ~25,000 125
Corn 20 ~59,000 2,500
Rice 24 45-56,000 441

* This list of resources in genetic mapping and linkage analysis (http://bioresearch.ac.uk/nb/c5272de5be6fc0cdf1153bbbf6ea7394.html) is as promising as anything so far. If all else fails, perhaps you could post a request for references on the bionet.genome.chromosomes (http://www.bio.net/hypermail/biochrom/) newsgroup?

* A nice introduction to genetic analysis (http://www.ncbi.nlm.nih.gov/About/primer/mapping.html)here, if you need something explained in plain(ish) English.

Have you any particular plant in mind? A lot more is known about some than about others, though very few have been fully sequenced. Sequencing of the maize genome (http://mednews.wustl.edu/news/page/normal/6180.html?emailID=7210), for instance, is just getting under way:

Maize is found in thousands of products in supermarkets and stores. The maize genome's 2.5 billion base pairs in 10 chromosomes make it nearly as long as the human genome, which has 2.9 billion base pairs in 23 chromosomes. When completed, maize will be the largest plant genome sequenced.

Although smaller than the human genome, the maize genome is estimated to contain approximately twice as many genes: 50,000 to 60,000 genes, while the human genome has about 26,000. The maize genome also has large repetitive stretches and regions devoid of genes that will make sequencing challenging.

* This Geocities article (http://www.geocities.com/geneinfo/facts/engineerfr.html) has a few good bits: ... plant cells are, not surprisingly, very different from those of humans. First, the nature of plant genetics makes it easier to insert and remove genes from the genome. In addition, plant seeds are accustomed to being exposed to harsh environmental conditions. Thus, plant cells can be relatively easily manipulated in the laboratory and then used to grow genetically modified crops. Genetic manipulation of some laboratory animals, such as flies and mice, is also routinely used in research.

In contrast, the technology available to manipulate human genes and embryos is not well developed. The human genome is unusually resistant to manipulation, so we currently do not have technology with allows the efficient removal and insertion of genes in human cells. Also, if it were ever to be done, human genetic engineering would have to be carried out on a zygote or very small embryo in a laboratory. Because the normal environment of a developing human embryo in the womb is very sheltered and controlled, the embryos are extremely sensitive to any handling. Currently, very small human embryos are handled in infertility clinics and in limited cases of screening for genetic disease. Even with the aid of powerful drugs and implantation of multiple embryos, the survival rate in these cases is still quite low. Given the difficulties in manipulation of human genes and the delicate nature of human embryos, our technology is far from being able to produce a genetically engineered human. ...