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Respiratory Changes During Germination of Urediospores of Puccinia graminis f. sp. tritici. Ramesh Maheshwari, Research Associate, Department of Botany, University of Michigan, Ann Arbor 48104; Alfred S. Sussman, Professor, Department of Botany, University of Michigan, Ann Arbor 48104. Phytopathology 60:1357-1364. Accepted for publication 6 April 1970. DOI: 10.1094/Phyto-60-1357.

Urediospores of Puccinia graminis f. sp. tritici germinated rapidly when agitated in a buffer containing nonyl alcohol and Tween 20 (polyoxyethylene sorbitan monolaurate). Synchronous and nearly complete germination occurred when urediospores were vapor-phase hydrated prior to use. This method permitted measurements of endogenous respiration of urediospores with an oxygen electrode during the germination process. The results were compared with those obtained using conventional manometric techniques. Initially the manometric measurements of respiratory rates were higher than the polarographic measurements, but as germination began the situation was reversed. The differences observed in the two methods of measurements were attributed to problems of wetting the spores, the drying out of germ tubes, and a metabolic restriction in Warburg respirometer flasks caused by the lack of carbon dioxide. The respiration of germinating urediospores, when measured with an oxygen electrode, was characterized by four distinct phases. Phase 1 was characterized by the development of respiratory activity upon contact of urediospores with liquid, preceding germination. Phase 2 was initiated by a decline in respiratory rate, during which germination was initiated. Phase 3 was marked by a second and greater increase in respiratory rate which paralleled the rate of germination and germ tube elongation. Phase 4 showed a gradual decline in respiratory rate which commenced after germination was completed and the germ tubes had grown more than half of their maximal length. In contrast to germinating spores, nongerminating ones incubated under conditions of self-inhibition did not show phase 3. The addition of the partially purified self-inhibitor of urediospore germination inhibited both respiration and germination, with the latter being more sensitive. The respiratory quotient of vapor-phase hydrated urediospores declined from an initial high value of 0.88 to lower values from 0.33 to 0.59. The respiratory pattern observed was suggestive of a qualitative change in urediospore metabolism during the progress of germination.