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

Abstract

Uredospores of wheat stem rust (Puccinia graminis Pers. f. sp. tritici Eriks. & E. Henn.) were deposited onto Millipore membranes and allowed to germinate. Those remaining continuously at 20° formed germ tubes only (non-differentiated), but those exposed to 30° for 90 min after the first 2 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 (1.65 × 106) and 18-S (0.80 × 106) ribosomal RNA (rRNA), 5-S (3.6 × 104) rRNA, and 4.5-S (2.4 × 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.

Early Changes in the Nucleotide Pools of Germinating Rust Uredospores

“…With Uromyces phaseoli uredospores a strong reduction of the phospholipid fraction during the first 20 min of germination was reported (LANGENBACH and KNOCHE 1971). Reduction of RNA, mainly ribosomal RNA, occurred in germinating uredospores of flax rust (QUICK 1973) and wheat stem rust (KIM and ROHRINGER 1974). Hence increases of nucleotide pools may indicate de novo synthesis or could also be the consequence of RNA degradation.…”