Paul J. Allen

Infection Structures from Rust Urediospores: Effect of RNA and Protein Synthesis Inhibitors

Urediospores of Puccinia graminis tritici, floated on buffer, produce infection structures when subjected briefly to 30�C soon after germination. Inhibitors of RNA synthesis interfere with the difierentiation of infection structures if present during this heat treatment. Inhibitors of protein synthesis prevent differentiation if present following heat treatment. Apparently infection structure formation is accompanied by synthesis of RNA, and the completion of infection structure development requires protein synthesis.

Identification of the Germination Self-Inhibitor from Wheat Stem Rust Uredospores

Two germination inhibitors from wheat rust uredospores were identified as the cis and trans isomers of methyl 4-hydroxy-3-methoxycinnamate (methyl ferulate). They are the self-inhibitors from these spores described previously.

Mode of action of methyl cis-ferulate, the self-inhibitor of stem rust uredospore germination

Abstract Germination of uredospores of Puccinia graminis var. tritici begins by digestion of the wall material next to the cytoplasm in the region of the pores (pore plugs) and progresses outward. The endogenous self-inhibitor, methyl-cis-ferulate prevents digestion of the pore plug at concentrations similar to those required to inhibit germination (10 to 100 nm ). Removal of the inhibitor allows digestion to proceed but it is interrupted if inhibitor is re-introduced before digestion has progressed to the outer periphery of the spore wall. Digestion is insensitive to inhibitors of RNA and protein synthesis. The data suggest that a preformed enzyme required for digestion of the plug is inhibited by the self-inhibitor. Removal of the inhibitor leads to reversal of the inhibition of this postulated enzyme and to the ensuiing rapid digestion of the plug.

Uredospore wall digestion during germination independent of macromolecular synthesis

Abstract Dissolution of the wall in the germ pore region of uredospores of Puccinia graminis tritici is completed within 30 min when spores are incubated in suspension in a medium containing a germination stimulant. The spores are immediately permeable to l -leucine, uracil and phosphorus, but impermeable to orotic acid. Uracil and phosphorus are incorporated into a macromolecule, which in the case of phosphorus was shown not to be RNA. l -Leucine is incorporation into protein from the first few minutes of incubation. Cycloheximide inhibits the incorporation of leucine without interference with wall dissolution. Methyl cis-ferulate, on the other hand, prevents wall dissolution but has no effect on l -leucine incorporation. Wall dissolution, the first observable phase of germination, does not therefore depend on RNA or protein synthesis, and inhibition of this step in germination by methyl cis-ferulate does not result from an inhibition of protein synthesis.