Ricerche al Microscopio Elettronico sui Tubercoli Radicali di Alcune Leguminose

Abstract

Electron microscope studies on root nodules of some leguminous plants. — From this study of ultrathin sections of root nodules of Pea, Bean and Kidney-bean plants, it has been possible to recognize the infrastructural changes which occur during the development of the root nodules, both in the special cells (containing Rhizobia) and in the intermediary cells (free of Rhizobia). With regard to the symbiotic bacteria it has been possible to ascertain that their penetration into root nodules occurs by means of an infection's thread (delimited by its own wall), which contains numerous Rhizobia dipped in an abundant mucilage, with which they, at the beginning, are released into the host plant's cells. The Rhizobia appear enveloped by three membranes, namely a thin citoplasmic membrane, a cell wall, and a « membrane envelope », this last looking at the beginning rather detached from bacterial cell, by the presence of mucillaginous substances which afterward become less and less reduced. The membrane envelope, which is common for several bacteria in the kidney-bean plants, surrounds instead a single bacterium in the pea and in the bean plants. The importance of this membrane seems to rely on the fact that, according to some Authors, it would be formed around the bactetia which are active in nitrogen fixation. Moreover, it has been possible to find out that, among the varous Leguminous plants studied, there are remarkable differences in the morphology of the bacteria as well as in their modifications during the evolution to bacteroid stage.