Obligater Parasitismus phytopathogener Pilze

Summary

• 1. By physiological investigations (Fehrmann, 1971 a, 1971 b) the ecologically obligate parasite Phytophthora infestans (Oomycetes, fam. Peronosporaceae) was compared with related species. In contrary to other species of the same genus, Phytophthora infestans is not able to persist saprophytically under natural conditions. According to previous results, the fungus is disordered in its energy metabolism. Main target of this paper is a comparison of the fine structure in the hyphae of Phytophthora infestans with that of Phytophthora erythroseptica, in order to find out, whether the mentioned physiological disorder is accompanied by changes in ultrastructure. Phytophthora erythroseptica is able to persist saprophytically and to parasitize living host plants as well.

• 2. In very young hyphae of Phytophthora erythroseptica the cytoplasma is free of vacuoles; in the numerous mitochondria the interior membrane systems are smaller than in later stages of development. In younger mycelium some endoplasmatic reticulum with cisternae was found, often neighbouring relatively high differentiated dictyosomes forming small vesicles. Cytosomes—smaller than mitochondria—with optically homogeneous content and a single membrane sometimes are connected with neighbouring mitochondria. With increasing differentiation the cytoplasma matrix is divided up into an optically dense and a less dense fraction. Gradual separation by membranes leads to the formation of extended vacuolar systems from the less dense fraction. In the fully developed stage the mitochondria are longish. Their interior, mostly tubular structures are of irregular and multi-form shape. In older hyphae their size is reduced drastically. The cytosomes increase in size somewhat with increasing age of the hyphae. A plasmalemma was observed in older mycelium only. Pores in the nuclear envelope are comparably big in diameter.

• 3. Older hyphae of Phytophthora infestans withstood all efforts in contrasting them sufficiently. Essentially the fine structure in young mycelium coincides with that of Phytophthora erythroseptica. However, the membrane structures in the interior of the mitochondria are much less multiform in shape. Apparently, during the formation of vacuoles membranes are formed at a very early stage.

• 4. The results gave no evidence for a primary disorder in the fine-structure of Phytophthora infestans. On the other hand, the different formation of the interior structures in the mitochondria may well be related to the defective energy metabolism of this fungus.

Zusammenfassung

• 1. In sehr jungen Hyphen von Phytophthora erythroseptica ist das Cytoplasma noch vacuolenfrei, die inneren Membransysteme der zahlreichen Mitochondrien kleiner als in späteren Entwicklungsstadien der Organelle. In jungem Mycel findet sich endoplasmatisches Reticulum in begrenztem Umfang, häufig in enger Nachbarschaft mit relativ hoch differenzierten Dictyosomen. Mit zunehmender Differenzierung kommt es zunächst zur Entmischung des Cytoplasmas in einen optisch dichteren und einen optisch weniger dichten Anteil; dies führt bei sukzessiver Membranabgrenzung schließlich zur Vacuolenbildung. In älteren Hyphen beherrschen das Bild große Vacuolensysteme. Die Mitochondrien sind in voll entwickeltem Zustand sehr langgestreckt, mit reich und unregelmäßig gestalteten, zumeist tubulär erscheinenden Innenstrukturen, die später stark reduziert erscheinen. In jungen Hyphen konnte die räumliche Beziehung von Cytosomen zu benachbarten Mitochondrien beobachtet werden. Ein Plasmalemma war erst in älterem Mycel erfaßbar.

• 2. Der Feinbau der Hyphen von Phytophthora infestans stimmt in den Grundzügen mit dem von Phytophthora erythroseptica überein. Membranstrukturen des Mitochondrien-Innenraumes sind jedoch weniger vielgestaltig. Bei der Vacuolenbildung kommt es offenbar schon früh zur Membranabgrenzung gegen das umgebende Grundplasma.