Help! chloroplast isolation

[Zhu Congju]

I have tried several routine protocols for the choroplast isolation and
cpDNA extraction from a wall-less algal cell (Isochrysis). Unfortunately,
none of them was successful. The EcoRI and BamHI disgestions did not turn
up anything but only one band on 1% argarose gel. I was wondering if the
homogenisation was too intense, because I could not find Yeda or French
press at the moment. Can I use ultrasonication as an alternative for the
cell repture?