title: Subcellular organization of N2-fixing nodules of cowpea (Vigna unguiculata) supplied with silicon.
abstract: Provision of silicon (0, 0.048, 0.096, 0.24, 0.48, and 0.96 g/l) in the form of silicic acid (H4SiO4) to nodulated cowpea plants (Vignia unguiculata [L.] Walp.) grown in liquid culture resulted in considerable changes in the internal organization of nodule structure. Compared to the control plants which received no added silicate, bacteroid numbers increased significantly (P < or = 0.05) at silicate concentrations of both 0.096 and 0.48 g/l. The number of symbiosomes also increased by 3.2-fold at the silicate concentration of 0.96 g/l compared to the control. In contrast, the size of bacteroids and symbiosomes decreased significantly (P < 0.05) inside nodules of silicate-treated plants. The peribacteroid space was also decreased considerably (P < 0.05) with the application of 0.096 and 0.96 g of silicate per liter to plants. However, the size of intercellular spaces adjacent to infected and uninfected interstitial cells within the nodule medulla increased significantly (P < or = 0.05) at 0.096 g of silicate per liter followed by a sharply marked (P < or = 0.05) decrease with each subsequent increase in silicate application. The result was a large decrease (P < 0.05) in the area of bacteria-infected tissue occupied by intercellular space at the highest silicate concentration, which was caused by a significant (P < or = 0.05) increase in cell wall thickness. Our findings show that the positive effects of silicon on N2 fixation might actually be due to an increased number of bacteroids and symbiosomes.
authors.affiliation: Department of Botany, University of Cape Town, Private Bag, Rondebosch 7701, South Africa.
authors.forename: A
authors.initials: A
authors.lastname: Nelwamondo
authors.forename: M A
authors.initials: MA
authors.lastname: Jaffer
authors.forename: F D
authors.initials: FD
authors.lastname: Dakora
mesh_terms: D002473:Cell Wall / Q000378:metabolism / Q000648:ultrastructure; D007887:Fabaceae / Q000378:metabolism* / Q000648:ultrastructure; D009586:Nitrogen Fixation; D018517:Plant Roots / Q000187:drug effects* / Q000382:microbiology* / Q000648:ultrastructure; D012824:Silicic Acid / Q000494:pharmacology*; D012825:Silicon / Q000378:metabolism
chemical_list: D012824:Silicic Acid; D012825:Silicon