Soybean (Glycine max. L.) and bacteroid glyoxylate cycle activities during nodular senescence

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

“…As shown in Fig. 2f, bacteroids are homogenous and rodshaped, in contrast to the diVerent shapes (oval or round) generally observed by TEM (Cohen et al 1986;Fargeix et al 2004). Moreover, we observed that some symbiosomes were going to merge (data not shown).…”

“…Indeed, King and Purcell (2005) demonstrated that the ureides may contribute to the feedback inhibition of nitrogenase activity speciWcally in soybean nodules. Furthermore, if we consider that the ureide accumulation coincides with the disappearance of nitrogenase transcripts, observed by Fargeix et al (2004), after 11 days of dark treatment, it can be argued that there is a possible down-regulation of nitrogenase at the transcriptional levels by the ureides. Because ureides are exported from the nodules to the shoots where they are catabolised, we suggest that the accumulation of the ureides in senescing nodules can be attributed to water deWcits and/or to the decrease in ureide catabolism in leaves Sinclair 2000, 2001).…”

“…This senescence is also observed in leguminous plants in response to environmental perturbations like drought, low temperature, defoliation, external addition of nitrogen and pathogenic attack (Cots et al 2002;Patriarca et al 2004;Puppo et al 2005). In addition, nodule senescence can be artiWcially triggered by exposing soybean plants to prolonged darkness (Cohen et al 1986;Gordon et al 1993;Fargeix et al 2004). Although dark-induced senescence is a premature phenomenon, it shares many of the molecular, physiological and ultrastructural characteristics found in naturally senescing nodules, such as the loss of nitrogenase activity, the increase in proteolytic activity and the greenish colour of nodule tissues (PfeiVer et al 1983;Cohen et al 1986;Jacobi et al 1994;Fargeix et al 2004).…”

“…In addition, nodule senescence can be artiWcially triggered by exposing soybean plants to prolonged darkness (Cohen et al 1986;Gordon et al 1993;Fargeix et al 2004). Although dark-induced senescence is a premature phenomenon, it shares many of the molecular, physiological and ultrastructural characteristics found in naturally senescing nodules, such as the loss of nitrogenase activity, the increase in proteolytic activity and the greenish colour of nodule tissues (PfeiVer et al 1983;Cohen et al 1986;Jacobi et al 1994;Fargeix et al 2004). Because natural senescence is an irreversible phenomenon, understanding the physiological processes which occur during induced senescence could help to Wnd strategies that delay this phenomenon and extend the active period of rhizobium-plant symbiosis (Espinosa-Victoria et al 2000).…”

“…It concerns the alteration of the structure of the symbiosomes, an organelle-like compartment in which bacteroids are surrounded by a specialised membrane called the peribacteroid membrane (Fargeix et al 2004;Van de Velde et al 2006). However, while this alteration is considered as the earliest observable event associated with a loss of nitrogen-Wxing activity, little information is available on the metabolic modiWcations during nodule senescence in soybean (Cohen et al 1986;Fargeix et al 2004;Van de Velde et al 2006). For these reasons, we performed further experiments to demonstrate unambiguously the autophagic process in relation to the down-regulation of the nitrogen metabolism.…”