Symbiotic nitrogen fixation is differentially affected by waterlogging in two Lotus species

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

Foz do Iguaçu

Congreso; 11th International Plant Molecular Biology Congress - 2015; 2015

Symbiotic Nitrogen Fixation (SNF) is efficiently carried out betweenlegume plants and rhizobia. However, SNF is greatly affected in waterlogged soils,where hypoxia occurs. Legumes of genus Lotusare important members of plant communities in grasslands and pastures. Althoughmost of them are generally considered tolerant to waterlogging, differences amongspecies responses have been found. In a preliminary study, weinoculated with Mesorhizobium lotitwo contrasting tolerance species, growing in nitrogen-free substrate exposedto 28 days of waterlogging (WL) or free-drainage (Control) conditions: L. japonicus ecotype "MG-20"(MG20) (sensible species) and L. tenuis(Lt) (tolerant species). Biomass andtissue nitrogen concentrations were evaluated. MG20 showed a sharply declined inthe measured parameters in WL compared to Control, while Lt values remainedconstants. Based on these results, we studied genesexpression of SNF (glutamine synthase and NifH subunit of nitrogenase) andfermentative metabolism (alcohol dehydrogenase and pyruvate decarboxylase) keyenzymes. Expression of genes encoding fermentation enzymes were increased in WLnodulated roots of both species. However genes expression levels of SNFmetabolism were strongly down-regulated in MG20 WL plants, whilst in a lessextent in Lt. Chlorophyll fluorescence parameters (Fv/Fm and PIabs)were also measured. Only MG20 waterlogged plants were affected. Though waterlogging stress causedhypoxia in nodulated roots of MG20 and Lt, SNF was affected differentiallybetween species. Consistently, chlorophyll fluorescence showed that MG20 ismore susceptible to waterlogging than Lt. Our study shows that differences betweenspecies could lead to understand waterlogging tolerance mechanism in animportant forage legume.