Primary leaves of two oat varieties were inoculated with Puccinia coronata Corda and the changes in ³²P incorporation into nucleic acid fractions were studied by MAK column chromatography.
In the susceptible variety, Victoria, the inoculated/uninoculated ratio of radioactivity in the rRNA fraction increased slightly at the initiation period of reproductive growth of the rust fungus (3 days after inoculation), then largely during the uredosorus development (4 to 5 days). The ratio in the sRNA fraction increased only at the beginning of sporulation (5 days). The change in the ratio for the TB-RNA as well as rapidly labeled RNA fractions showed a similar trend to that for the rRNA fraction.
In the resistant variety, Shokan No.1, the increases in the ratio were noted to be of similar extent among the sRNA, rRNA, and TB-RNA fractions: being slight at the prehaustorial stage of infection (20hr after inoculation), and thereafter being large until 48hr. The rapidly labeled RNA was also increased by infection.
The base analysis of labeled RNA's indicated that the increased synthesis of rRNA may be originated from the rust fungus in the susceptible leaves, and from the host in the resistant leaves.