Caffeic acid decreases salinity-induced root nodule superoxide radical accumulation and limits salinity-induced biomass reduction in soybean

Abstract

Caffeic acid (3,4-dihydroxycinnamic acid; CA) is a cinnamic acid occurring naturally in a variety of plant species. In this study, the effects of caffeic acid (100 μM caffeic acid) on soybean root nodule superoxide content, cell viability and superoxide dismutase (SOD; EC 1.15.1.1) activity were evaluated in the presence and absence of salinity stress (imposed by application of 70 mM NaCl), along with the effects of CA on growth of soybean in the presence or absence of salinity. Treatment with CA caused a decrease in superoxide content, enhanced cell viability and SOD activity, with changes in SOD activity accounted for by increased activity of two manganese SOD isoforms and one copper/zinc SOD isoform. Furthermore, CA improved soybean growth under salinity but reduced soybean biomass in the absence of salinity. We suggest that CA improves soybean salinity stress tolerance, possibly via signals that regulate accumulation of reactive oxygen species (ROS) during salinity stress.