Biochemical responses of wheat to silicon application under salinity

Background: Salinity is one of the main threats that can cause crop yield losses by limiting plant growth. Several important cultivated crops including wheat exhibit sensitivity to salt stress by severe yield reductions. Approaches to improve salt resistance are critical for improved food production in the future. Aims: Silicon (Si) is well known for its role as quasi-essential element to enhance growth and development of monocot food crops, especially under a variety of abiotic and biotic stress conditions. However, the mechanism of Si-induced stress resistance is still not fully understood. Here, we investigate the biochemical basis of Si-induced salt resistance of wheat. Methods: Effect of Si treatment on wheat plants under salt stress was measured by biochemical studies of photosynthetic pigments, ions, oxidative stress indicators, enzymatic and non-enzymatic antioxidant systems, phytohormones along with expression of two Si-transport genes. Results: Our results suggest that Si-induced salt resistance of wheat involves a signaling cascade that triggers the biochemical defense responses. Salinity induces production of the stress hormone abscisic acid that upregulates the expression of Si-influx transporter gene TaLsi1 and Si-efflux transporter gene TaLsi2, in the presence of soluble Si in cytosol, and this triggers jasmonate-mediated activation of both enzymatic and non-enzymatic antioxidant systems along with osmolyte production. Moreover, peculiar stoichiometric changes in photosynthetic pigments after Si application, as signatures of shaded condition, also lead us to the hypothesis that insoluble Si phytoliths in plants may aid a physical defense response by creating a "mechanically shielded leaf microenvironment" against a variety of abiotic and biotic stress conditions. Conclusion: This study demonstrates that Si activates biochemical defense responses against salt stress in wheat plants.