Establishment and physiological responses of the Rhizobium tropici-Leucaena leucocephala symbiosis in presence of phenanthrene and naphtalene

This study evaluated the establishment of the symbiosis between Rhizobium tropici CIAT899 and Leucaena leucocephala (Lam.) under contaminated systems with naphtalene (NAF) and phenanthrene (FEN), as well as the physiological plants responses such as total content of phenolic compounds (CFT), total antioxidant activity (AAT) and the content of chlorophylls (CloroT) and carotenoids (CaT). After 31 days, NAF had more significant negative effects on nodulation by delaying the formation of nodules until the day 25 at 100 mg/L. In the presence of 20 mg FEN/L, L. leucocephala plants did not show significant differences on the number of nodules when compared to the control, while nodulation decreased 52 % at 60 and 100 mg FEN/L. Inoculation with R. tropici resulted in significant increases of PST (>150 %) in comparison to non-inoculated plants. The foliar content of CFT was significantly greater at non-inoculated treatments in respect to those with R. tropici, and significantly higher in plants exposed to FEN than NAF. For both hydrocarbons, the concentration of 100 mg/L resulted in greater CFT and AAT when compared to 20 or 60 mg/L. For roots, treatments without contamination and R. tropici had more content of CFT and AAT. The AAT in nodules significantly increased due to NAF, while a significant reduction was observed in FEN treatments. Either NAF or FEN did not significantly affect the content of CloroT, although this content was significantly greater in plants with R. tropici than non-inoculated plants. The CaT content significantly increased at non-inoculated plants exposed to NAF and/or FEN.Original Abstract: Este estudio evaluo el establecimiento de la simbiosis entre Rhizobium tropici CIAT899 y Leucaena leucocephala (Lam.) en sistemas contaminados con naftaleno (NAF) y fenantreno (FEN) y la respuesta de la planta con el contenido de compuestos fenolicos totales (CFT), actividad antioxidante total (AAT) y contenido total de clorofilas (CloroT) y carotenos (CaT). A los 31 dias, el NAF tuvo efectos negativos en la formacion de nodulos, retardando su aparicion hasta el dia 25 en presencia de 100 mg/L. Ante 20 mg FEN/L, las plantas de L. leucocephala no mostraron diferencias significativas en la formacion de nodulos con respecto al testigo, mientras que a 60 y 100 mg FEN/L la nodulacion disminuyo significativamente en 52 %. La inoculacion con R. tropici incremento el peso seco total (PST) hasta en 150 % comparado con las plantas no inoculadas. El CFT en hoja fu