We are interested in the integrity of nucleic acids as a result of storage and processing.  Depending upon the application, the size of DNA fragments may have a significant impact on an experiment, and we have observed significant fragmentation created during sample processing as well as during storage before processing.  For instance, bead beading with small grinding media reduced DNA fragments to less than the 17 Kb (the upper marker for the Bioanalyzer).  Larger grinding balls had a much less significant impact, as did traditional grinding with mortar and pestle.

However we also observed some breakdown of DNA at various storage temperatures.  Refrigerated samples were relatively stable, but then degraded rapidly (we assume from bacterial contamination).  Frozen (-20 C) samples were typically degraded.  However ultralow and cryogenically stored samples showed a mix of stability.  We posted this info with some data on our blog (see link).

In reviewing the literature, we find that the methods for sampling and storing are highly variable.  Some researchers press leaves, others store samples on silica gel, others freeze, some freeze dry, etc.  Is there a consensus as to how samples should be handled when harvested, and then subsequently stored?  Is the methodology dependent upon downstream applications? 

Any input would be very helpful.  Thank you.

http://opsdiagnostics.com/blog/DNA-Integrity-and-Storage-bp3.html