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Mit Hilfe einer Os-Fixation unter bestimmten Bedingungen ist es möglich, in den Nukleoiden von 5 verschiedenen Bakterienarten ein feinfädiges Nukleoplasma zu erhalten. Abweichungen von der Standardfixation führen zu den üblichen, mehr oder weniger groben Einschlüssen in einer leeren Kernvakuole. Ein PH von 6, die Anwesenheit von Aminosäuren oder Peptiden während der Osmiumfixation und eine Stabilisierung mit Uranylacetat erwiesen sich als wesentlich, um ein feines Nukleoplasma zu erhalten. Die äußere Form der Kernvakuole ist sehr variabel und für die Teilungsphasen nicht spezifisch. Die biologischen Konsequenzen dieser Beobachtungen werden diskutiert und eine Hypothese betreffend die Mechanismen der Fixation des Nukleoplasmas aufgestellt.

The invasive properties of Azoarcus sp. strain BH72, an endorhizospheric isolate of Kallar grass, on gnotobiotically grown seedlings of Oryza sativa IR36 and Leptochloafusca (L.) Kunth were studied. Additionally, Azoarcus spp. were localized in roots of field-grown Kallar grass. To facilitate localization and to assure identity of bacteria, genetically engineered microorganisms expressing 0-glucuronidase were also used as inocula.P-Glucuronidase staining indicated that the apical region of the root behind the meristem was the most intensively colonized. Light and electron microscopy showed that strain BH72 penetrated the rhizoplane preferentially in the zones of elongation and differentiation and colonized the root interior inter-and intracellularly. In addition to the root cortex, stelar tissue was also colonized; bacteria were found in the xylem. No evidence was obtained that Azoarcus spp. could reside in living plant cells; rather, plant cells were apparently destroyed after bacteria had penetrated the cell wall. A common pathogenicity test on tobacco leaves provided no evidence that representative strains of Azoarcus spp. are phytopathogenic. Compared with the control, inoculation with strain BH72 significantly promoted growth of rice seedlings. This effect was reversed when the plant medium was supplemented with malate (0.2 g/liter). N2 fixation was apparently not involved, because the same response was obtained with a nifK mutant of strain BH72, which has a Nif-phenotype. Also, Western blot (immunoblot) analysis of protein extracts from rice seedlings gave no indication that nitrogenase was present. PCR and Western immunoblotting, using primers specific for eubacteria and antibodies recognizing type-specific antigens, respectively, indicated that strain BH72 could colonize rice plants systemically, probably mediated by longitudinal spreading through vessels.

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