Gel electrophoresis is extremely useful for identifying single and double stranded DNA and RNA fragments from plants, and preparative gels are used for recovery of nucleic acids. Many aqueous solutions, stored concentrated and buffered to a specific pH (usually with EDTA), are used to make the gels (with acrylamide/bis-acrylamide stock solution for PAGE gels), and as running buffers. DNA running speeds vary with buffer, and buffer circulation or replacement can prevent them from becoming exhausted. MOPS-EDTA-sodium acetate (MESA) running buffer is most commonly used for RNA electrophoresis in denaturing formaldehyde-agarose gels, and for separation of RNA prior to membrane transfer for Northern blot analysis. Tris Acetate-EDTA (TAE) buffer is commonly used for DNA agarose gel electrophoresis and non-denaturing RNA agarose gel electrophoresis. Tris-Borate-EDTA (TBE) running buffer is used for DNA and RNA polyacrylamide gel electrophoresis, with non-denaturing or denaturing (7 M urea) gels and in DNA automated sequencing gels and agarose gels.