Role of reactive oxygen species generation and Nod factors during the early symbiotic interaction between bradyrhizobia and peanut, a legume infected by crack entry

Aims We evaluated whether reactive oxygen species ( ROS ) production and the plant antioxidant system are involved in the symbiotic interaction between bradyrhizobia and legumes infected by crack entry, without intracellular infection threads ( IT ) formation, such as A rachis hypogaea L. (peanut). The role of bradyrhizobial Nod factors ( NF ) in modulating the plants’ oxidative burst was also analysed. Methods and Results Histochemical and quantitative procedures were used to detect ROS levels in inoculated and in NF ‐treated peanut roots. Increase in root H 2 O 2 production was determined at 10 min postinoculation with B radyrhizobium sp. SEMIA 6144 or after NF addition. ROS production was modulated by NF . From 15 to 30 min postinoculation, the compatibility of B radyrhizobium sp.–peanut interaction depends mostly on the H 2 O 2 detoxification via catalase. Conclusions We demonstrated for the first time that the early events of the symbiotic interaction in legumes invaded by crack entry trigger an increase in ROS production (represented exclusively by a higher H 2 O 2 content) in which NADPH ‐oxidase seems not to be involved. NF modulate this response by enhancing the plant antioxidant machinery, contributing to the creation of adequate conditions for symbiosis development. Significance and Impact of the Study Our data provide new insights into the mechanism involves in the symbiotic interaction that establish legumes infected by crack entry and suggest that ROS response shows differences compared with legumes invaded by IT formation.