Exogenous application of l‐histidine suppresses bacterial diseases and enhances ethylene production in rice seedlings

Exogenous application of l ‐histidine enhances resistance to pathogens in tomato ( Solanum lycopersicum ) and Arabidopsis thaliana via activation of the ethylene ( ET )‐dependent signalling pathway. In this study, the efficacy of l ‐histidine for suppression of bacterial diseases in rice seedlings was investigated. Rice seeds were soaked in 10 m m l ‐histidine, 10 m m l ‐lysine, or distilled water ( DW ) as a control for 48 h at 28 °C to stimulate germination. Treated seeds were then vacuum‐inoculated with Burkholderia glumae or B. plantarii . Seedling diseases caused by both of these bacterial pathogens were suppressed by treatment with l ‐histidine but not by treatment with l ‐lysine or DW . Expression of an ET ‐responsive defence‐related gene, OsGLP8‐12 , was induced by treatment of seeds with l ‐histidine. As diseases were not suppressed in rice seedlings treated with l ‐histidine after vacuum‐inoculation, pretreatment of rice seedlings with l ‐histidine before inoculation might activate the plant immune system. Indeed, ethylene production and the abundance of 1‐aminocyclopropane‐1‐carboxylic acid ( ACC ) synthase 2 ( OsACS2 ) transcript increased in healthy seedlings grown from rice seeds treated with l ‐histidine but not in those treated with DW . Furthermore, treatment of rice seeds with ACC , an ethylene precursor, suppressed bacterial rice seedling rot caused by B. glumae as effectively as did treatment with l ‐histidine, whereas treatment of rice seeds with aminooxyacetic acid, an inhibitor of ACC synthase, partially compromised disease suppression. Taken together, l ‐histidine seems to suppress bacterial rice seedling diseases via an ethylene‐dependent resistance pathway.