DETECTION AND MINIMIZATION OF BACTERIAL COMPONENTS IN BARLEY DNA

Four types of bacteria were found in the extracts of barley tissues following inadequate surface sterilization of seeds prior to germination. The buoyant densities of their DNA were 1.700, 1:714, 1719 and 1721 g cm-3. Silver nitrate treatment of seeds reduced the extent of bacteria from more than 106 to 105colonies per gram of tissue and the types from 4 to 2. The number of bacterial colonies were always less in shoots than in roots.

While shoot DNA displayed a single peak at 1.700 g cm-8 in a CsCl gradient DNA from root extracts showed 3 additional peaks (1.714, 1.719 and 1.724 g cm-3) when seeds were not sterilized before germination. The buoyant densities of the three additional peaks in DNA preparations from roots correspond well with that of the three bacterial types. The fourth type's DNA has the same bouyant density as that of the barley main band DNA. It was estimated that the contribution of contaminant DNA in the total DNA preparation could be less than 0.025 per cent at the reduced contamination level following silver nitrate treatment. The present findings raise doubts about the claims of bacteria DNA uptake and integration by barley seeds.