An unusual infection mechanism and nodule morphogenesis in white lupin (Lupinus albus)

Abstract

Summary• The infection of white lupin ( Lupinus albus ) roots and the early stages in organogenesis of the lupinoid nodule are characterized in detail in this work.• Immunolabelling of Bradyrhizobium sp. ( Lupinus ) ISLU16 and green fluorescent protein labelling of Mesorhizobium loti NZP2037, two strains that induce nodulation in L. albus , allowed us to monitor the infection and morphogenesis process. Light and transmission electron microscopy, low-temperature scanning electron microscopy, fluorescence and confocal microscopy were employed.• Rhizobia penetrated the root intercellularly at the junction between the root hair base and an adjacent epidermal cell. Bacteria invaded the subepidermal cortical cell immediately beneath the root hair through structurally altered cell wall regions. The newly infected cell divided repeatedly to form the central infected zone of the young nodule. Bacteria seemed to be equally distributed between the daughter cells.• A new mode of direct epidermal infection and an unusual morphogenesis for indeterminate nodules lead to the formation of the lupinoid nodule with unique characteristics.

The evolution of determinate and indeterminate nodules within the Papilionoideae subfamily

“…S4-6). This is similar to Lupinus nodules in which it has previously been reported that cells remain mitotically active after release of rhizobia into the cytoplasm (Gonzalez-Sama et al, 2004;. Thus, all studied Indigofera species form determinate nodules and have the ability to form secondary clusters of dividing cells.…”

“…In some legumes, rhizobia enter their host by other mechanisms, such as transcellular penetration (crack-entry) between cells. This is for example the case in some Sesbania, Aeschynomene and Lupinus species (Gonzalez-Sama et al, 2004;Bonaldi et al, 2010;Capoen et al, 2010).…”

“…This nodule type is characterized by the presence of two lateral meristems, by which nodules encircle the roots (Golinowski et al, 1987). Another characteristic is that the infected cells remain mitotically active and the symbiosomes are equally distributed between the daughter cells (Gonzalez-Sama et al, 2004;. This mitotic activity might be facilitated by the absence of infection threads in these nodule cells (Lotocka et al, 2000;Gonzalez-Sama et al, 2004).…”

“…Another characteristic is that the infected cells remain mitotically active and the symbiosomes are equally distributed between the daughter cells (Gonzalez-Sama et al, 2004;. This mitotic activity might be facilitated by the absence of infection threads in these nodule cells (Lotocka et al, 2000;Gonzalez-Sama et al, 2004). Aeschynomenoid nodules are characterized by the fact that central infected tissue contains no uninfected interstitial cells.…”

Overexpression of Flavodoxin in Bacteroids Induces Changes in Antioxidant Metabolism Leading to Delayed Senescence and Starch Accumulation in Alfalfa Root Nodules

“…Semithin sections for light microscopy were stained with 1% (w/v) toluidine blue in aqueous 1% sodium borate for direct observation with a Zeiss Axiophot photomicroscope (Oberkochen). Ultra-thin sections for transmission electron microscopy were processed as reported previously (González-Sama et al, 2004).…”