Plasmodesmata distribution and sugar partitioning in nitrogen-fixing root nodules of Datisca glomerata

Abstract

To understand carbon partitioning in roots and nodules of Datisca glomerata, activities of sucrose-degrading enzymes and sugar transporter expression patterns were analyzed in both organs, and plasmodesmal connections between nodule cortical cells were examined by transmission electron microscopy. The results indicate that in nodules, the contribution of symplastic transport processes is increased in comparison to roots, specifically in infected cells which develop many secondary plasmodesmata. Invertase activities are dramatically reduced in nodules as compared to roots, indicating that here the main enzyme responsible for the cleavage of sucrose is sucrose synthase. A high-affinity, low-specificity monosaccharide transporter whose expression is induced in infected cells prior to the onset of bacterial nitrogen fixation, and which has an unusually low pH optimum and may be involved in turgor control or hexose retrieval during infection thread growth.Electronic supplementary materialThe online version of this article (doi:10.1007/s00425-010-1285-8) contains supplementary material, which is available to authorized users.

MtSWEET11, a Nodule-Specific Sucrose Transporter of Medicago truncatula

“…Increased frequencies of plasmodesmata have been documented in nodules of legumes (Complainville et al, 2003) and the non-legume, Datisca glomerata (Schubert et al, 2011). In nodule primordia of Medicago sativa, plasmodesmata among stele, pericycle, endodermis, and cortex cells were significantly more abundant compared to noninoculated root controls (Complainville et al, 2003).…”

“…In nodule primordia of Medicago sativa, plasmodesmata among stele, pericycle, endodermis, and cortex cells were significantly more abundant compared to noninoculated root controls (Complainville et al, 2003). In D. glomerata root nodules induced by Frankia spp., extensive plasmodesmal connections were observed between all cell types of the nodule, including mature infected cells (Schubert et al, 2011).…”

“…Suc breakdown in root nodules, and more generally in higher plants, is mediated by Suc synthases and invertases (Morell and Copeland, 1984;Winter and Huber, 2000). Nodule-upregulated genes encoding Suc synthases and invertases have been isolated and characterized in several legumes and one actinorhizal species (Küster et al, 1993;Gordon and James, 1997;Gordon et al, 1999;Baier et al, 2007;Horst et al, 2007;Welham et al, 2009;Schubert et al, 2011). Suc synthase is necessary for efficient N-fixation in Pisum sativum (Gordon et al, 1999), M. truncatula (Baier et al, 2007), and Lotus japonicus (Horst et al, 2007).…”

“…It is also capable of transporting Gal, Xyl, and Man, albeit at much lower rates. Because of the specific increase of DgSTP1 transcripts in infected nodule cells and an unusually low pH optimum of the protein, it has been suggested to fulfill the function of Glc export toward symbiotic bacteria prior to the onset of N-fixation (Schubert et al, 2011).…”

“…A proposed function for LjSUT4 is efflux of sugars stored in the vacuole for use in the cytoplasm. Another sugar transporter induced in N-fixing nodules, DgSTP1, was characterized in the nonlegume, D. glomerata (Schubert et al, 2011). DgSTP1 belongs to the sugar porter (SP) family and has the highest relative uptake rate for Glc.…”