DNA was extracted from fresh spinach leaves in DNAzol (Invitrogen, part of Life Technologies) by PCT and by a standard bead-beater protocol. Prior to pressure cycling, spinach was ground for 20 seconds in the PCT shredder. PCT extraction was performed for 30 cycles at 35,000 psi. Bead-beater extraction was performed in a bead beater for 10 10-second pulses with 1 mm zirconia beads.
Since bead beating generates a large amount of heat, samples were placed on ice between bead-beating pulses to prevent overheating. Following sample disruption by PCT or bead beating, DNA was extracted from the DNAzol as recommended by the manufacturer.
After DNA purification, triplicate samples were analyzed by electrophoresis. Analysis by gel electrophoresis shows that bead beater-extracted DNA is highly sheared, while PCT-extracted genomic DNA exhibits much less shearing (Figure 3). After extraction by PCT or bead beating, DNA was purified using the DNAzol isolation protocol for plants according to manufacturer’s instructions.