40 
The host cells for experiments on recombinant DNAs may be cells 
in culture, in seedling or plant parts, or in whole plants. Cells in 
whole plants that cannot be adequately contained should not be used 
as hosts for shotgun experiments at this time, and attempts to infect 
whole plants with DNA recombinants cloned elsewhere should not be 
initiated until their effects on host cells in culture, seedlings, 
or plant parts have been studied. 
Organelle or plasmid DNAs or DNAs of viruses of low pathogenicity 
to plants may be used as vectors. In general, the same preference 
criteria for selecting host-vectors given in the preceding section on 
animal systems apply to plant systems, where organelle and plasmid DNAs 
can be grouped together as offering the potential of highly contained 
vectors that should be investigated. 
Experiments on recombinant DNAs formed between the initial moderately 
contained vectors and DNA from cells of species in which the vector DNA 
can replicate, either autonomously or as an integrated segment of the 
cell's genome, should use P2 physical containment--provided that the 
source of the DNA is itself not pathogenic or known to carry pathogenic 
agents, or to produce products dangerous to plants. In the latter cases, 
of if the vector is an unmodified virus of low pathogenicity, the ex- 
periments should be carried out under P3 conditions. 
Experiments on recombinant DNAs formed between the above vectors 
and DNAs from other species can also be carried out under P2 if that DNA 
has been purified 10 and determined not to contain harmful genes. Other- 
10 TheDNA preparation is defined as purified if the desired DNA represents 
at least 99% (w/w) of the total DNA in the preparation, provided that it 
was achieved or verified by more than one procedure. 
[Ill] 
