SEPTAL PORES IN THE HETEROBASIDIOMYCETIDAE, PUCCINIA GRAMINIS AND P. RECONDITA

The septal pores in uredial mycelium of Puccinia graminis and P. recondita lack the septal swelling and septal pore cap (dolipore-parenthosome configuration) typically associated with the pores of previouslyinvestigated Homobasidiomycetidae and the Tremellales among the Heterobasidiomycetidae. The pores in young hyphae of these two species of Puccinia are characterized by the presence of a cytoplasmic matrix which apparently occludes the pore and acts as a plug, thus preventing the migration of organelles from cell to cell. Large vesicles are typically present at the periphery of the pore matrix and the matrix may be very incompletely bounded by a membrane. Nuclei and other cytoplasmic structures migrate from cell to cell through an opening in the septum lateral to the pore. The available evidence indicates that this peripheral gap in the septum results from a breakdown of a portion of an initially complete septum rather than from incomplete septum formation. In addition to the centripetally formed septa, the hyphae of P. graminis and P. recondita are further compartmentalized by shallow infoldings of the lateral wall and limited unilateral septum formation. There is apparent free passage of cellular material between adjacent compartments. MoORE and McAlear (1962) published a series of electron micrographs showing septal pores in five species of Ascomycetes and five species of Basidiomycetes. They proposed that the type of septal pore was an ultrastructural morphological feature distinguishing Ascomycetes from Basidiomycetes. The Ascomycetes investigated were shown to have pores which were simple holes, whereas the Basidiomycetes studied were characterized by elaborate "dolipore-parenthosome" septa. Micrographs showing septal pores of a similar nature in Polystictus versicolor had previously been published (Girbardt, 1958, 1961) and have subsequently been reported in a number of other Homobasidiomycetidae (Bracker and Butler, 1963; Berliner and Duff, 1965; Manocha, 1965; Wells, 1965; Wilsenach and Kessel, 1965; Hyde and Walkinshaw, 1966) and in three Heterobasidiomycetidae (Tremellales) (Moore and McAlear, 1962; Wells, 1964). However, this type of elaborate septum was not found in the aecial thallus of Puccinia podophylli (Moore, 1963) or in the uredial mycelium of Puccinia graminis tritici (Ehrlich and Ehrlich, 1963) and Melampsora lini (Manocha and Shaw, 1967). 1 Received for publication 6 February 1968. This investigation was supported by the National Institutes of Health Research Grant No. 5-ROl Al 06378. The authors express their sincere appreciation to Dr. W. Q. Loegering, Cereal Crops Division, Agricultural Research Service, USDA, Beltsville, Md., for the supply of seed and initial urediospore cultures of Puccinia graminis tritici. The technical assistance of Mr. T. Ledoux and Mr. T. McGrath, Department of Biological Sciences, Duquesne University, also is gratefully acknowledged. 2Present address: Department of Plant Pathology, Kansas State University, Manhattan. Giesy and Day (1965) reported that both simple pores and pores having the characteristic septal swelling and pore cap are present in the Homobasidiomycetidae, Coprinus lagopus. The simple pores in this species occur only in heterokaryotic mycelia and apparently arise via a degeneration of the more complex pores. Jersild, Mishkin, and Niederpruem (1967) reported similar simple septa in various common A heterokaryons of Schizophyllum commune, and they also postulate that these simple septa arose via a degeneration of originally complex septa. The reports of Ehrlich and Ehrlich (1963), Moore (1963), and Manocha and Shaw (1967) suggest that septal swellings and pore caps are not characteristic of all basidiomycete septa, particularly of some of the Heterobasidiomycetidae. In view of the phylogenetic implications involved in the septal pore structure of the Basidiomycetes and the recurrent interest in nuclear migration in the Uredinales, the present investigation was initiated to study in greater detail the septa in two species of Puccinia. MATERIALS AND METHODS-Primary leaves of 6or 7-day-old wheat plants, Triticum aestivum L., were inoculated with urediospores of an isolate of race 56, or a selection obtained from a cross of races 111 X 36 of Puccinia graminis Pers. f. sp. tritici Erikss. and E. Henn., or race 104B of P. recomdita Rob. ex Desm. f. sp. tritici. Wheat varieties used included 'Little Club,' 'Timstein 6B,' 'Reliance,' and selections from 'Chinese Spring.' Specimens for electron microscopy were harvested 3, 4, 5, 6, 7, and 9 days after inoculation.