Making Specialised A Local Blast Db

Hi,

I need to make a local Blast DNA (nt) database that only includes sequences from plants. I'd also like to make one with only chloroplast sequences. Put I can't find any tools to do this. I don't want to download the entire nt and then use masking. I'd rather be using a smaller db.

Are there tools to do this? update_blastdb.pl does not seem to be able to 'filter' sequences.

I can use Entrez to get a subset nt, but can't see a way to download the output (the download browser buttons don't work for this - the download always freezes).

Thanks,

T.