Biochemical Changes in Terminal Root Galls Caused by an Ectoparasitic Nematode, Longidorus africanus - Nucleic Acids.

Changes in DNA and RNA in roots of bur marigold fed upon by Longidorus africanus were studied using analytical methods, radioactive precursors, and analytical CsC1 density-gradient centrifugation. The analyses showed that almost twice as much RNA and DNA was present in parasitized root tips as in those of nonparasitized control plants. Studies on the rates of incorporation of labeled thymidine and uridine confirmed the DNA levels determined by analytical methods, but revealed a much higher incorporation rate of RNA in healthy root tips than in those attacked by L. africanus. However, (3)(2)P incorporation followed by DNase and RNase digestion showed that the seemingly greater amount of RNA in healthy root tips was due to a rapid formation of a pool of unlabeled uridine following infection.The possibility that L. africanus injected DNA into roots during feeding was examined by the density-gradient centrifugation method, with negative results. However, the rapid increase of RNA precursors in the parasitized roots might have been caused by injection of plant virus particles during nematode feeding.