Ribonucleic acids of differentiating and non-differentiating uredosporelings of wheat stem rust

摘要

Uredospores of wheat stem rust (Puccinia graminisPers. f. sp.triticiEriks. amp; E. Henn.) were deposited onto Millipore membranes and allowed to germinate. Those remaining continuously at 20deg; formed germ tubes only (non-differentiated), but those exposed to 30deg; for 90ensp;min after the first 2ensp;h of germination developed infection structures corresponding to appressoria and substomatal vesicles (differentiated).Nucleic acids were extracted with a phenol method from resting uredospores and from differentiated and non-differentiated sporelings. The amount of extractable RNA decreased as germination progressed, but no RNA was detected in the germination medium. The decrease in extractable RNA (up to 40) occurred in both differentiated and non-differentiated sporelings.Acrylamide gel electrophoresis was used to separate RNA species and to determine their approximate molecular weights (in daltons): sporelings contained 25-S (1.65ensp;times;ensp;106) and 18-S (0.80ensp;times;ensp;106) ribosomal RNA (rRNA), 5-S (3.6ensp;times;ensp;104) rRNA, and 4.5-S (2.4ensp;times;ensp;104) transfer RNA (tRNA). Radioactive uridine, fed to sporelings, was incorporated mostly into 5-S rRNA and (or) tRNA.Acrylamide gel electrophoresis and sucrose density gradient centrifugation revealed that differentiated sporelings contained a type of RNA that was not detected in non-differentiated sporelings. It was heterogeneous and migrated in the 16-S to 5-S interval on polyacrylamide gels. Some of the RNA present in this fraction may have been preformed in resting spores and released from more complex material during the process of differentiation.