Biological nitrogen fixation is differentially affected by waterlogging in two Lotus species.

ANTONELLI C.; CALZADILLA P.I.; BORDENAVE C; ESCARAY, F.J; RUIZ O.A.

Congreso; 11 International Congress of Plant Molecular Biology; 2015

Biological Nitrogen Fixation (BNF) is efficiently carried out in legumes, in symbiosis with rhizobia. However, BNF is greatly affected in waterlogging stress conditions, were hypoxia occurs. Legumes of genus Lotus are important members of plant communities in grasslands and pastures. Although they are considered tolerant to waterlogging, differences between species response have been found. In a preliminary study, we inoculated with Mesorhizobium loti two tolerant contrasting species growing in waterlogging (WL) or free drainage (Control) conditions: L. japonicus ecotype "MG-20" (MG20) (sensible species) and L. tenuis (Lt) (tolerant species). Biomass and tissue nitrogen concentrations were evaluated. MG20 showed a sharply declined in the measured parameters in WL compared to Control, while Lt values remained constants. Based on these results, we studied genes expression of BNF (glutamine synthase and NifH) and fermentative metabolism (alcohol dehydrogenase and pyruvate decarboxylase) key enzymes. Nodulated MG20 and Lt were grown on nitrogen-free substrate and exposed to 28 days of WL or Control treatments. Expression of genes encoding fermentation enzymes were increased in WL nodulated roots of both species. However genes expression levels of BNF metabolism were down-regulated in the stress treatment, and in a less extent in Lt than in MG-20. Chlorophyll fluorescence parameters (Fv/Fm and PI abs) were also measured. Only MG20 waterlogged plants were affected. As a conclusion, though waterlogging stress caused hypoxia in nodulated roots of MG20 and Lt, BNF was affected differentially between species. Chlorophyll fluorescence showed that MG20 is more susceptible to waterlogging than Lt. Our study demonstrated that differences between species could lead to understand waterlogging tolerance mechanism in an important forage leguminosae.