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

Abstract

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.

Homospermidine synthase contributes to salt tolerance in free-living Rhizobium tropici and in symbiosis with Phaseolus vulgaris

“…5), as previously observed in nodules of M. sativa (López-Gómez et al 2014a). This unusual PA may be produced specifically by the bacteroids during the symbiosis since the differentiation process from free-living bacteria into bacteroids implies a global change in the metabolic profile, including an increment in the Homspd level, three times more abundant in bacteroids than in cultivated rhizobia according to Vauclare et al (2010). The wide distribution of Homspd among a variety of nitrogen-fixing rhizobia (Fujihara 2009) suggests that it might play a role in relation to N 2 fixation.…”

The Legume Root Nodule: From Symbiotic Nitrogen Fixation to Senescence

“…Thus, SIS is a much faster process than developmental senescence. Moreover, whereas developmental senescence is associated with the establishment of the nodule senescent zone which increases over time, SIS induces the degeneration of the whole nodule in a short time period (Matamoros et al, 1999;Perez Guerra et al, 2010;Vauclare et al, 2010). At the structural level, microscopic analyses also show that developmental senescence and dark stress-induced senescence present different features in M. truncatula.…”

“…As stated before, BNF is a highly energetic process which requires a constant energy supply. Modification of nodule sucrose content has been observed during drought stress (Galvez et al, 2005;Gordon et al, 1997), salt stress Lopez et al, 2008;Sanchez et al, 2011;Lopez et al, 2009;Ben Salah et al, 2009), dark stress (Gogorcena et al, 1997;Matamoros et al, 1999;Vauclare et al, 2010) and cold stress (Walsh & Layzell, 1986;van Heerden et al, 2008). However, whereas dark stress induces a diminution of sucrose concentration, www.intechopen.com drought stress, salt stress and cold stress lead in general to its accumulation in nodules.…”

Plant Responses to Sugar Starvation

“…by using HPLC (Morkunas et al 2010), nuclear 1HNMR spectroscopy (Brouquisse et al 2007, Kim et al 2007, and 13 C and 31 P-NMR spectroscopy (Vauclare et al 2010, Gout et al 2011. Electron paramagnetic resonance (EPR) spectroscopy is applied to measure free radicals (Morkunas et al 2004.…”