Synergistic effect of brassinosteroids on salt-induced inhibition of nodule formation in Lotus japoicus.

Abstract

We present here the effects of sodium chloride (NaCl) and brassinosteroids (BRs) on nodulation of Lotus japoicus. When Lotus seedlings were inoculated with rhizobia on a medium containing 100-150 mM NaCl, the number of nodules was slightly reduced compared with that on the same medium free of NaCl. Growth enhancement of the seedlings due to symbiotic fixation was rarely observed in this condition. Moreover, white-colored nodules were increased, in which leghemoglobins are supposed not to function properly. Interestingly, rhizobia harbored in white-colored nodules were much larger in number than those in red-colored ones. In the presence of more than 175 mM NaCl, nodulation hardly occurred. By contrast, neither applications of the most bioactive BR, brassinolide (BL) nor a specific inhibitor of BR biosynthesis, brassinazole influenced nodulation in the absence of NaCl. However, BL treatment at 10^-8 M or more obviously enhanced the inhibition of nodule formation caused by NaCl.