Isopropanol precipitation problem - (May/22/2009 )

Just a little update on our isopropanol problem. It seems that Isek was right on the point regarding contamination with polyphenol compounds in the sample. We are trying to extract DNA from field grown tomato plants showing strong viral symptoms (stunting, leaf curling, mosaics, leaf deformations) for viral identification using PCR. The "bubble" appears during DNA extraction of these samples. For comparison, we used cotyledon leaves from cucumber seedlings and the bubble was absent!. We are going to try some modification to the protocol or use a different one:)
Thanks for the input...

Tubes on the left show the "bubble" (tomato), samples on the right without "bubble" (cucumber seedlings)