It has already been reported that rice dwarf virus (RDV) contains double-stranded RNA and that RDV-RNA is easily separated from host cell nucleic acids by methylated albumine-kieselguhr column chromatography and also by cellulose column chromatography. These procedures make it possible to screen such substances which inhibit the incorporation of
32P into RDV-RNA but do not inhibit the
32P-incorporation into ribosomal RNA (rRNA). Two grams of uppermost and second leaves detached from RDV-infected rice plants were placed in a test tube containing 2m
l of aqueous solution of an antibiotic and 60μc of
32P-H
3PO
4 and kept under greenhouse conditions. After whole the solution was almost absorbed by the leaf sample, 3m
l of water was added to the tube. After 24 hours, nucleic acid was extracted by phenol method and one fourth of the nucleic acid preparation was subjected to cellulose column chromatography. Optical densities at 260nm of rRNA and RDV-RNA and radioactivities of both RNA's were measured. Inhibitory effect of an antibiotic for the syntheses of both RNA's was evaluated by the decrease of cpm/OD
260 values. Cycloheximide at 2μg/g fresh weight inhibited the incorporation of
32P into both rRNA and RDV-RNA equally suggesting that the antibiotic is phytotoxic. This was indeed the case when the antibiotic was applied to RDV-infected rice plants at 2ppm through culture solution, i.e., the plants died within 2 weeks. Blasticidin S at 3μg/g and kasugamycin at 160μg/g fresh weight rather stimulated the
32P-incorporation into both rRNA and RDV-RNA, whereas at higher dosages, 6μg/g and 320μg/g respectively, they inhibited the
32P-incorporation into both RNA's but only very slightly. When these were applied to infected plants through culture solutions at liminal concentrations, i.e., 2 and 40ppm respectively, throughout the whole life period, there was no sign of the recovery of normal growth.
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