Birdsfoot trefoil (Lotus corniculatus) root nodules: morphogenesis and the effect of forage harvest on structure and function

Abstract

Nodule structure, nodule enzymes of ammonia assimilation, nitrogenase-dependent acetylene reduction, and nodule soluble protein were studied during vegetative regrowth of detopped birdsfoot trefoil (Lotus corniculatus L.) seedlings grown in the glasshouse. Nodules senesced rapidly for a period of 14 days following shoot removal, but then pink nodule populations increased as shoot regrowth occurred. The structural sequence of senescence was similar in nodules whether the result of either aging or shoot removal. Membranes surrounding bacteroids showed degenerative changes as bacteroids senesced. Bacteroids aggregated within the nodule cells and ultimately disappeared in senescent cells. Infection threads and bacteria inside infection threads did not disintegrate.Nodule senescence as a result of shoot removal was accompanied by a marked decline in acetylene reduction, nodule soluble protein, nodule host plant glutamine synthetase (GS), and glutamate synthase (GOGAT). Nodule enzyme activity, soluble protein, and acetylene reduction activity recovered to initial values as shoot regrowth occurred and pink nodule populations increased. Nodule host plant glutamate dehydrogenase (GDH) did not change after shoot removal.This study shows that birdsfoot trefoil nodules respond to shoot removal by an increased senescence. Recovery of nodule function is associated with the formation of a new nodule population. The data also indicate that host plant GS and GOGAT function to assimilate fixed N. Spherical nodules with determinant growth may be less efficient than elongate nodules with indeterminant growth in nodule maintenance and function.

Root nodulation of Sesbania rostrata

“…More shown that A. caulinodans ORS571, the strain used as an inoculant in this study, also produces lipooligosaccharidic Nod factors (21). In S. rostrata, these factors elicit the division of cortical cells at the axils of lateral roots (21) (16) and Lotus corniculatus (40). Infection droplets containing several bacteria have also been noted for Vigna radiata (25).…”

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

“…One route for infection occurs in lateral roots of both flooded and non-flooded L. uliginosus, which were infected via root hairs. This is the most commonly observed infection process in typical indeterminate and determinate temperate and\or crop legumes , where newly-formed root hairs are the most infectible sites (Hirsch, 1992), and has been reported previously with non-flooded L. corniculatus and L. japonicus (Ranga Rao, 1977 ;Vance et al, 1982 ;Szczyglowski et al, 1998).…”

“…In these nodules, infection threads were much smaller and relatively scarce ( Fig. 4c) compared with earlier stages and, as with L. corniculatus and L. japonicus (Vance et al, 1982 ;Szczyglowski et al, 1998), further development of the infected tissue was by division and expansion of already infected cells, rather than by new infections. In contrast to MAC236, MAC265 labelled infection threads and infection droplets relatively lightly (compare the silver-enhanced sections in Fig.…”

“…Moreover, all plants showed acetylene reduction activity (results not shown), suggesting that at least some nodules contained active nitrogenase. As nodules did not form on flooded L. corniculatus, and as the infection and\or nodule development process of L. corniculatus under well drained conditions did not differ from that described in previous studies (Ranga Rao, 1977 ;Vance et al, 1982), it was decided to concentrate on the hitherto undescribed development of flooded L. uliginosus nodules. Unless stated otherwise, all the nodules examined were 0n6 mm in diameter, were white because they contained no Lb (Vance et al, 1982), and gave no reaction with the antibody to nitrogenase component II (results not shown, but see Fig.…”

“…Lotus spp. will form nitrogen (N # )-fixing nodules with Mesorhizobium loti (Ranga Rao, 1977 ;Pankhurst et al, 1979 ;Vance et al, 1982 ;Wood et al, 1985) and Bradyrhizobium sp. (Wood et al, 1985), and these nodules are spherical and hence classically determinate in morphology Hirsch, 1992).…”