Colonization and invasion of peanut (Arachis hypogaea L.) roots by gusA-marked Bradyrhizobium sp.

Abstract

Tufted rosettes of long root hairs occur in axils of young lateral roots of peanut (Arachis hypogaea L.). Analyses of serial sections of the axils of emerging lateral roots revealed multiple layers of root hair cells. The cells of the outer layer partially overlie the adjacent cells of the inner layer. When Bradyrhizobium cells with an integrated gusA gene were inoculated onto peanut roots and the roots subsequently stained with X-gluc, blue spots indicating the presence of colonies of Bradyrhizobium were observed in the axils of lateral roots. Blue spots were also observed in other areas on the root surface. Transmission electron microscopy revealed that the primary wall of the base of root hair cells has a loose construction. Upon inoculation of Bradyrhizobium, bacteria entered only between root hair cells through the middle lamella. In other areas of the root surface other than axils of lateral roots, the cells had modified walls similar to those at the base of root hair cells. However, invasion by Bradyrhizobium of the cell wall was not observed.Key words: Arachis hypogaea, gusA-marked Bradyrhizobium, cell wall, invasion, root hair cell, root nodules.

Distribution Pattern of Root Nodules in Relation to Root Architecture in Two Leading Cultivars of Peanut (Arachis hypogaeaL.) in Japan

“…However, our observations showed that nodules were rarely formed on the taproot and were mainly formed on the 1st-order lateral roots in both peanut cultivars (Table. 3). Root nodules of peanut have been reported to develop mainly at the emergence site of lateral roots after the invasion of microorganisms into the root through cracks on the parental roots, which were caused by the emergence of lateral roots (Boogerd and van Rossum, 1997;Uheda et al, 2001), although nodule formation often occurs at the site of root hair formation in many other leguminous species. Most nodules of peanut formed on the 1st-order lateral roots in this study, probably because many 2nd-order lateral roots emerged from the 1st-order lateral roots.…”

“…Nodule formation in peanut is known to differ from that of many other legumes. Root nodules develop only at sites of lateral root emergence in peanut, whereas the nodulation often occurs at sites of root hair formation in other legumes (Uheda et al, 2001). However, information on nitrogen fi xation in peanut is limited compared with that of soybean and common bean (Bell et al, 1994;Khan and Yoshida, 1994;Daimon et al, 1999;Daimon and Yoshikawa, 2001).…”

Nitrogen-Fixing Activity of Root Nodules in Relation to Their Size in Peanut (Arachis hypogaea L.)

“…Although peanut (Arachis hypogaea L.) is an important legume crop in rotation, information on nitrogen fixation in peanut is fewer compared with that in soybean and common bean (Bell et al, 1994;Khan and Yoshida, 1994;Daimon et al, 1999;Daimon and Yoshikawa, 2001). Nodule formation in peanut is known to differ from that in many other legumes: root nodules develop only at the sites of lateral root emergence in peanut, whereas nodulation often occurs at the sites of root-hair formation in other legumes (Uheda et al, 2001). Therefore, more information on the distribution pattern and nitrogen-fixing activity of individual root nodules in peanut is necessary for better understanding and more effective utilization of their nitrogen fi xation.…”

Involvement of Root Hair during <i>Rhizobial</i> Invasion in Cultivated Peanut (<i>Arachis hypogaea</i> L.)

“…No IT observation during peanut rhizobial infection may mean that root hair might not be necessary for peanut root infection by Bradyrhizobia, since the involvement of root hair often results into the formation of ITs [10]. Bradyrhizobia enter peanut root through an intercellular path, where the epidermal and cortical cells have altered cell walls [11].…”

“…Several studies indicated that for intercellular crack entry, rhizobia invade the root at the site of lateral root emergence but none of these studies addressed the role of RoH [11] [12]. However, Chandler [7] stated that infection of peanut only occurs in the presence of root hair and where root hair has large basal cells.…”