Stress-Induced Declines in Soybean N2 Fixation Are Related to Nodule Sucrose Synthase Activity

Abstract

Fixation of N, by legume root nodules can be rapidly and severely inhibited by a range of environmental perturbations, including defoliation, drought, salinity, and application of nitrate. Stress can also be induced by experimental approaches such as placing plants in prolonged darkness (Gordon et al., 1993;Gogorcena et al., 1997). One explanation for this decline in N, fixation in response to stress is that the ODB operates to reduce O, flux into the nodule and thus prevent damage to nitrogenase activity Hunt and Layzell, 1993). However, the means by which such stresses can induce the operation of the ODB have not yet been established.Recently, the idea that the ODB is solely responsible for the control of nodule N, fixation during stress has been challenged (Guérin et al., 1990; Diaz de1 Castillo et al., 1994; Diaz de1 Castillo and Layzell, 1995) because nodule metabolic potential is also impaired in response to drought stress. However, the primary effect is unclear. It could be the reduced import of photosynthates, which means that less carbohydrate is available for nodule function (however, see Durand et al., 1987), or the reduced demand for N This work was funded through the Biotechnology and Biolog-

Nitrogen fixation is synchronized with carbon metabolism inLotus japonicusandMedicago truncatulanodules under salt stress

“…In addition, L. japonicus presented higher SS and AI activities than M. truncatula, in accordance with its higher nitrogenase activity. It has been previously hypothesized that there is a close link between ANA and the capacity of the nodule to metabolize sucrose (Gordon et al 1997. In particular, SS activity was more sensitive to salt stress as compared with AI, in agreement with previous works that have established that nodule sucrose synthase are particularly sensitive to stress (Gonza´lez et al 1995;Gordon et al 1997).…”

“…A strong correlation between sugar accumulation and osmotic stress tolerance has been widely reported (Gilmour et al 2000;Streeter et al 2001;Taji et al 2002), which support a higher tolerance of L. japonicus nodules to salt stress. M. truncatula nodules did not show nodule carbohydrate accumulation; however, amino acids accumulated in these nodules by NaCl, which could be explained as a consequence of damage produced by saline stress, in accordance with results of Gordon et al (1997), Soussi et al (1998) and Khadri et al (2007) in nodules of soybean, chickpea and common bean, respectively.…”

“…It has been assumed the accumulation of organic solutes in response to salt stress is involved in protection mechanisms such as the restoration of the cell volume and turgor, the reduction of the cell damage induced by free radicals, the protection and stabilization of enzymes and membrane structures (Bartels and Sunkar 2005). Salinity is known to boost the nodular carbohydrate content and sucrose is the predominant carbohydrate in legume root nodules (Fouge`re et al 1991;Gordon et al 1997). It has been argued that the accumulation of sucrose under salinity, associated with inhibition of the sucrose hydrolytic enzyme sucrose synthase (Arrese-Igor et al 1999), induces a deficiency of carbon for bacteroids with the subsequent inhibition of nitrogenase activity (Hunt and Layzell 1993).…”

The Response of Carbon Metabolism and Antioxidant Defenses of Alfalfa Nodules to Drought Stress and to the Subsequent Recovery of Plants

“…Studies on soybean (Glycine max), common bean (Phaseolus vulgaris), and pea (Pisum sativum) have shown that the inhibitory effects may be mediated by a decrease in nodule O 2 permeability (Durand et al, 1987;Serraj and Sinclair, 1996;Ramos et al, 1999) and metabolic activity (Díaz del Castillo and Layzell, 1995). The finding that the activity of Suc synthase (SS), but not other carbon and nitrogen metabolism enzymes, rapidly declined in nodules upon imposition of stress provided strong evidence for a major role of SS in the inhibition of N 2 fixation (González et al, 1995;Gordon et al, 1997;Ramos et al, 1999). A detailed biochemical analysis of the rug4 mutant of pea, which displays severely reduced SS activity, further demonstrated an essential role of SS in symbiosis .…”

Stress-Induced Legume Root Nodule Senescence. Physiological, Biochemical, and Structural Alterations

“…Many other important alterations related to oxygen, carbon, and nitrogen metabolism occur in nodules during senescence, but the precise sequence of these biochemical changes is far from clear (Carroll et al, 1987;Layzell et al, 1990;Gordon et al, 1997). There is also a paucity of information regarding the structural changes involved in stressinduced nodule senescence.…”