Efficacy of a bacterial siderophore, pyoverdine, to supply iron to Solanum lycopersicum plants.

Active uptake of ferric iron in microorganisms is based on siderophores. During iron deficiency, Pseudomonas fluorescens synthesizes siderophores, called pyoverdine, which have a high affinity for ferric iron. Strategy I plants generally cannot synthesize pyoverdine or take up ferric iron. We assessed the effect of pyoverdine chelated to ferric iron on iron nutrition in Solanum lycopersicum . Weight and photosynthetic pigment concentrations in the plants supplemented with the pyoverdine and ferric iron were restored to the rates of plants supplemented with ferrous iron. Leaves and roots accumulated significant iron after pyoverdine and ferric iron supplementation than when supplemented with ferric iron alone. When leaves and roots were supplemented with pyoverdine and ferric iron, the SlFRO1 expression level was suppressed to 20% and 50% relative to those decreased with ferric iron alone, respectively. The level of SlIRT1 in roots supplemented with pyoverdine and ferric iron decreased to 50% compared with the level in roots supplemented with ferric iron alone. These results suggest that SlFRO1 and SlIRT1 expression levels were suppressed and that iron content was restored by pyoverdine and ferric iron supplementation. Thus, the downregulation may have occurred because of negative feedback on mRNA expression. Pyoverdine-mediated ferric iron uptake by tomato is suggested to be a useful strategy to increase iron uptake from the environment.