Root nodulation of Sesbania rostrata

Abstract

The tropical legume Sesbania rostrata can be nodulated by Azorhizobium caulinodans on both its stem and its root system. Here we investigate in detail the process of root nodulation and show that nodules develop exclusively at the base of secondary roots. Intercellular infection leads to the formation of infection pockets, which then give rise to infection threads. Concomitantly with infection, cortical cells of the secondary roots dedifferentiate, forming a meristem which has an "open-basket" configuration and which surrounds the initial infection site. Bacteria are released from the tips of infection threads into plant cells via "infection droplets," each containing several bacteria. Initially, nodule differentiation is comparable to that of indeterminate nodules, with the youngest meristematic cells being located at the periphery and the nitrogen-fixing cells being located at the nodule center. Because of the peculiar form of the meristem, Sesbania root nodules develop uniformly around a central axis. Nitrogen fixation is detected as early as 3 days following inoculation, while the nodule meristem is still active. Two weeks after inoculation, meristematic activity ceases, and nodules then show the typical histology of determinate nodules. Thus, root nodule organogenesis in S. rostrata appears to be intermediate between indeterminate and determinate types.

Invasion of Lotus japonicus root hairless 1 by Mesorhizobium loti Involves the Nodulation Factor-Dependent Induction of Root Hairs

“…For example, in the semiaquatic S. rostrata, a close relative of L. japonicus, a crack entry mechanism at the sites of lateral root emergence is used as the principal mode of bacterial entry for nodule colonization under hydroponic conditions (Goormachtig et al, 2004a(Goormachtig et al, , 2004b. This mechanism manifests itself as the formation of pockets of bacteria embedded in the intercellular matrix that narrow down to intracellular infection threads prior to entering the plant cells (Sprent and Raven, 1992;Ndoye et al, 1994;Subba-Rao et al, 1995). Interestingly, in Chamaecytisus proliferus (tagasaste)-Bradyrhizobium sp.…”

Development of N2‐fixing nodules on the wetland legume Lotus uliginosus exposed to conditions of flooding

“…This second mode of infection appears to occur where there are no root hairs and follows a pattern similar to that observed within roots of Sesbania rostrata, Lupinus angustifolius, Mimosa scabrella and Mimosa pellita (Ndoye et al, 1994 ;Tang et al, 1992 ;De Faria et al, 1988 ;Loureiro et al, 1998). For example, like S. rostrata (Ndoye et al, 1994) and L. angustifolius (Tang et al, 1992), nodule initiation can occur in the region of the lateral root that lies within the tap root cortex, far from the region of root hair development. Furthermore, as with M. pellita (Loureiro et al, 1998), it appears that enlarged cells comprising the aerenchyma on flooded roots are most susceptible to infection.…”

Rhizobial and Actinorhizal Symbioses: What Are the Shared Features?

“…In legumes infected via intercellular penetration of the epidermis, rhizobia can proceed toward the nodule primordium cells in different ways. In some legumes, such as Sesbania rostrata and Neptunia sp, infection threads are formed in the cortex after intercellular penetration of the epidermis (see, for example, Tsien et al, 1983;Ndoye et al, 1994;Subba-Rao et al, 1995). These examples represent intermediates between intercellular and intracellular infection routes.…”

“…Alternatively, Frankia strains, and in some cases, rhizobia, can enter the root by penetrating the middle lamella between intact epidermal cells (Miller and Baker, 1985;de Faria et al, 1988;Racette and Torrey, 1989;Ndoye et al, 1994). In the roots of actinorhizal plants infected intercellularly, bacteria move through the cortex toward the nodule primordium intercellularly and become intracellular only when they are taken up into primordium cells in a process resembling infection thread formation ( Figure 1B; Miller and Baker, 1985;Racette and Torrey, 1989).…”