Barley preferentially activates strategy-II iron uptake mechanism under iron deficiency

Abstract

Plants utilize two main strategies for iron (Fe) uptake from the rhizosphere. Strategy-I is based on the reduction of ferric (Fe3+) to ferrous (Fe2+) iron by ferric chelate reductase (FCR) and is mainly observed in dicots. Strategy-II utilizes the complexation of Fe3+ with phytosiderophores secreted from the plant roots and mainly evolved in Gramineous species, including barley (Hordeum vulgare). Recent studies suggest that some species use a combination of both strategies for more efficient Fe uptake. However, the preference of barley for these strategies is not well understood. This study investigated the physiological and biochemical responses of barley under iron deficiency and examined the expression levels of the genes involved in Strategy-I and Strategy-II mechanisms in the roots. Fe deficiency led to decreased root and shoot lengths, fresh and dry weights, and Fe accumulation in the roots. Parallel to the chlorosis observed in the leaves, FCR activity and rhizosphere acidification were also significantly reduced in the roots, while the release of phytosiderophores increased. Furthermore, Strategy-II genes expressed higher than the Strategy-I genes in the roots under Fe deficiency. These findings demonstrate that Strategy-II is more activated than Strategy-I for Fe uptake in barley roots under Fe-deficient conditions.