Membrane peribacteroid

Nickel availability to the host plants severely limits the expression of the R. leguminosarum hydrogenase genes in the P. sativum symbiosis (Brito et al. 1994) and probably in other symbioses such as M. loti-L. corniculatus (Brito et al. 2000). This limitation occurs at the level of processing of the enzyme subunits (Brito et al. 1994). It is not clear, however, whether Ni limitation is due to the bacterial or the plant component of the symbiosis. Recent results of nickel transport experiments with intact pea symbiosomes indicate that the peribacteroid membrane is not a specific barrier for Ni transport into the bacteroid (Bascones et al. unpublished). 

Successful infection proceeds simultaneously with nodule morphogenesis triggered by the signal compounds produced by Rhizobium in response to its host, and leads to the release of bacteria from the infection threads into the cortical cells. Concomitantly, the bacteria are enveloped in a host-derived plasma membrane called the peribacteroid membrane (PBM) (Verma et al., 1978 Robertson et al., 1978). Both host- and bacterium-derived proteins are specifically targeted to this membrane (Fortin et al., 1985, 1987 Katinakis Verma, 1985 Katinakis et al., 1988), making it a unique subcellular compartment. 

Fig. 2. Proposed topology of soybean nodulin-26 in the peribacteroid membrane a-f, six membrane-spanning domains. T, Phosphorylation sites , potential glycosylation sites that are not glycosylated 0, gly-cosylation site facing the bacteroid is in fact glycosylated as shown by Con-A binding , trypsin target site closer to the first and last transmembrane domains , phosphate residues possibly interacting with the membrane.

Day, D. A., Ou Yang, L.-J. Udvardi, M.R. (1990). Nutrient exchange across the peribacteroid membrane of isolated symbiosomes. In Nitrogen Fixation Achievements and Objectives, ed. P.M. Gresshoff, L.E. Roth, G. Stacey W.E. Newton, pp. 219-26. New York Chapman and Hall. 

Fortin, M.G., Morrison, N.A. Verma, D.P.S. (1987). Nodulin-26, a peribacteroid membrane nodulin, is expressed independently of the development of the peribacteriod compartment. Nucleic Acids Research 15, 813-24. 

Katinakis, P. Verma, D.P.S. (1985). Nodulin-24 gene of soybean codes for a peptide of the peribacteroid membrane and was generated by tandem duplication of an insertion element. Proceedings of National Academy of Sciences (USA) 82, 4157-61. 

Mellor, R.B., Christense, T.M.I.E. Werner, D. (1986). Choline kinase II is present only in nodules that synthesize stable peribacteroid membranes. Proceedings of the National Academy of Sciences (USA) 83, 659-63. 

Morrison, N. Verma, D.P.S. (1987). A block in the endocytotic release of Rhizobium allows cellular differentiation in nodule but affects the expression of some peribacteroid membrane nodulins. Plant Molecular Biology 7, 51-61. 

Robertson, J.G., Lyttleton, P., Bullivant, S. Grayston, G.F. (1978). Membrane in lupin root nodules I. The role of Golgi bodies in the biogenesis of infection threads and peribacteroid membranes. Journal of Cellular Science 30, 129-49. 

Verma, D.P.S., Miao, G.-H., Joshi, C.P., Cheon, C.-I. Delauney, A. (19906). Internalization of Rhizobium by plant cells targeting and role of peribacteroid membrane nodulins. In Plant Molecular Biology 1990, ed. R.G. Herrmann B.A. Larkins, pp. 121-30. New York Plenum Press. 

Werner, D., Morschel, E., Garbers, C., Bassarab, S. Mellor, R.B. (1988). Particle density and protein composition of the peribacteroid membrane from soybean root nodule is affected by mutations in the microsymbiont Bradyrhizobium japonicum. Planta 174, 263-70. 

Perotto, S., VandenBosch, K.A., Butcher, G.W., Brewin, N.J. Molecular composition and development of the plant glycocalyx associated with the peribacteroid membrane of pea root nodules. Development 112 (1991) 763-773. 

Fig. 2. Transmission electron micrograph (16,000x enlargement) through an infected root cell of a soybean plant. The subcellular organelles of the host cell [mitochondria and plasts (a)] are present at the periphery of the cell adjacent to the host cell wall (b). The nitrogen-fixing bacteroids (c) are kept apart from the host cell cytoplasm (the location of leghemoglobin) by the peribacteroid space (d) and the peribacteroid membrane (e), which regulates transport of materials to and from the bacteroids.

Fig. 14. Quenching by peribacteroid membranes (PBMs) of the dimerization process of Fe(III) Lb in the presence of H202. Fe(III) Lb (210 /liM) was incubated with H202 (420 fj,M) for 1 h in the absence (lane 2) or in the presence of PBMs at the following protein concentrations 0.23 mg/mL (lane 3), 1.16 mg/mL (lane 4) and 2.33 mg/mL (lane 5). Lane 1 represents Fe(III) Lb alone and lane 6 and 7 PBMs plus H202 and PBMs alone, respectively (reprinted with permission from Moreau, S. Davies, M. J. Mathieu, C. Herouart, D. Puppo, A. J. Biol. Chem., 1996,271, 32557-32562).

Fig. 3. Bacteroid in the plant cell cytoplasm near the cell wall. A Golgi body occurs close to the peribacteroid membrane. Plasma membrane, pi peribacteroid membrane, pb bacteroid envelope outer membrane, bo bacteroid envelope inner membrane, bi bacteroid, b Golgi body, g.

Fig. 4. Segment of the bacteroid envelope and peribacteroid membrane at high magnification. Peribacteroid space, pbs. The region between the bacteroid envelope inner and outer membranes is the periplasmic space.

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