02415nam a2200325 a 450000100080000000500110000800800410001910000210006024501160008126000410019730000100023849000230024850000560027152015440032765000280187165000150189965000160191465000140193065000140194465000140195865000140197265000120198665000160199865000090201465000140202365000130203765300120205065300090206265300180207116215221996-01-24       1978    bl uuuu  m   00u1 u    #d1 aUMALI-GARCIA, M.  aEarly events in the establishment of an associative symbiosis of Azospirillum brasilense sp 7 with grass roots.  aFlorida: University of Floridac1978  a103p.  aTese de Doutorado.  aTese de Doutorado. Orientada por: David H. Hubbell.  aThe objectives of this study were to document by light and electron microscopy the events leading to the successful establishment of an associative symbiosis of Azospirillum brasilense sp 7 with the roots of a grass host under axenic conditions and to define physiological and biochemical interactions of the association suggested by the ultrastructural studies. The association between grass roots and Azospirillum brasilense sp 7 was investigated by the Fahraeus glass slide technique for axenic plant culture. Young inoculated roots of pearl millet and guinea grass produced more mucigel, more root hairs and more lateral roots than did the uninoculated controls. Within 12 h after inoculation cells of A. brasilense sp 7 were embedded in the mucigel at the root capand along the root axis. The bacteria were also firmly adsorbed to root hairs and epidermal cells but supplementing the medium with combined nitrogen reduced the adherence to root hairs. Preincubation in root exudate enhanced ability of the bacteria to attach firmly to root surfaces. The active root exudate factor is non-dialyzable and is inactivated by protease. Examination of the grass rhizosphere by electron microscopy revealed azospirilla enclosed within a slime layer with high affinity for electron dense materials normally associated with the host root cell wall. The bacteria entered the root tissue through lysed root hairs, open spaces created by sloughing of epidermal cells and lateral root emergence, and afterward invaded the middle lamellae of .......  aAzospirillum brasilense  amicroscopy  arhizosphere  asymbiosis  aBactéria  aGramínea  aGramineae  aMétodo  aMicroscopia  aRaiz  aRizosfera  aSimbiose  aMethods  aRoot  aSchizomycetos