Fatty Acid Composition of the Peribacteroid Membrane and the ER in Nodules ofGlycine maxVaries after Infection by Different Strains of the MicrosymbiontBradyrhizobiumjaponicum

Metabolic and structural rearrangement during dark-induced autophagy in soybean (Glycine max L.) nodules: an electron microscopy and 31P and 13C nuclear magnetic resonance study

The effects of dark-induced stress on the evolution of the soluble metabolites present in senescent soybean (Glycine max L.) nodules were analysed in vitro using (13)C- and (31)P-NMR spectroscopy. Sucrose and trehalose were the predominant soluble storage carbons. During dark-induced stress, a decline in sugars and some key glycolytic metabolites was observed. Whereas 84% of the sucrose disappeared, only one-half of the trehalose was utilised. This decline coincides with the depletion of Gln, Asn, Ala and with an accumulation of ureides, which reflect a huge reduction of the N(2) fixation. Concomitantly, phosphodiesters and compounds like P-choline, a good marker of membrane phospholipids hydrolysis and cell autophagy, accumulated in the nodules. An autophagic process was confirmed by the decrease in cell fatty acid content. In addition, a slight increase in unsaturated fatty acids (oleic and linoleic acids) was observed, probably as a response to peroxidation reactions. Electron microscopy analysis revealed that, despite membranes dismantling, most of the bacteroids seem to be structurally intact. Taken together, our results show that the carbohydrate starvation induced in soybean by dark stress triggers a profound metabolic and structural rearrangement in the infected cells of soybean nodule which is representative of symbiotic cessation.

Comparison of Mg2+-dependent ATP hydrolase activities of pea nodule symbiosomes and of pea root plasmalemma, obtained by an aqueous polymer two-phase system

The characteristics of the Mg2+-dependent ATPase activity from the peribacteroid membrane of pea symbiosomes was compared with that from pea root plasma membranes. Enzyme inhibitors, optimum reaction pH, substrate specificity and antibody recognition were the main parameters examined. Both the symbiosomes and the root plasma membrane were purified with an aqueous polymer two-phase system (APS). The final concentration of the APS for the purification of symbiosomes were: 6.3% w/w dextran T500, 6.3% w/w poly(ethylene glycol) 3350, 5 mM KH2PO4-K2HPO4, 5 mM KCl, 0.33 M sucrose, (pH 7.85); for the root plasma membrane was: 6.2% (w/w) dextran T500, 6.2% poly(ethylene glycol) 3350, 330 mM sucrose, 5 mM K2HPO4 and 4 mM KCl (pH 7.8). The lack of contamination of pea symbiosomes with endoplasmic reticulum, mitochondria, broken bacteroids and/or tonoplast vesicles was established. Similarly, the aqueous two-phase system used here provided a fairly enriched root plasma membrane with low cross-contamination from other sources. Both symbiosomal and root plasma membrane ATPase activities were highly specific to ATP. The symbiosome ATPase apparently corresponds to an E1E2-ATPase mechanism, similar to that found at the plasma membrane. The similarity between these two ATPases was further supported by immuno-analysis. Mg2+-ATPase of pea symbiosome and root plasma membranes were very similar, by all parameters tested.

The effect of different temperatures on the fatty acid composition of Rhizobium leguminosarum bv. viciae in the faba bean symbiosis

Fatty acid composition was determined in cells of strains CBhS and CBp7 of Rhizobium leguminosarum bv. viciae grown at four temperatures (10, 15, 22 and 30°C), and in bacteroids and nodules formed with faba bean (Vicia faba L.) grown at two day/night temperature regimes (22/15 and 15/10°C). Growth temperature markedly affected the fatty acid composition of free-living bacteria in both strains studied, and both showed similar variations at each temperature. The proportion of unsaturated fatty acids increased significantly with lowering of temperature. The major fatty acid found in bacteria and bacteroids was cis-vaccenic (C18: 1^Δ11 ), which comprised up to c. 78 (bacteria) and 56% (bacteroids) of total fatty acids. The presence of polyunsaturated fatty acids (linoleic (C18:^Δ,9,12 ) and linolenic (C18:3^Δ9,12,15 ) acids) was noted only in bacteroids, indicating changes following the differentiation of bacteria into bacteroids in the nodules. The fatty acid composition of nodules was similar to that of bacteroids, although major differences were found in their proportions. The different day/night temperature regimes had contrasting effects in bacteroids and in nodules. In bacteroids of both strains, the proportions of stearic (C18:0) and linoleic (C18:^Δ9,12 ) acids decreased at the lower temperature regime. In nodules, the proportion of stearic (C18:0) acid decreased, while that of linolenic (C18:3^Δ9,12,15 ) acid increased at the lower temperature regime. However, those of cis-vaccenic (C18:1^Δ11 ), linoleic (C18:^Δ9,12,15 ) and palmitic (C16:0) acids increased or decreased depending on the rhizobial strain. The proportion of unsaturated fatty acids increased with the lowering of temperatures in bacteroids of both strains, and varied in whole nodules depending on the strain. Strain CBp7 showed a greater symbiotic efficiency (dry matter yield) than strain CBh5 under both temperature regimes, but no relationship was found with the proportion of unsaturated fatty acids of bacteria, bacteroids or nodules.