Re-translocation of photoassimilates by Nano-TiO2 spraying in favor of osmotic adjustment in water-stressed sunflower

Abstract

Abstract Background Water deficit is one of the main environmental stresses that modifies the biomass allocation patterns between shoots and roots. Any attempt to improve the water status of plants, especially in regions of water scarcity, will be significantly important. In this study, the effect of foliar application of nanoparticles or ordinary TiO2 on water status of Helianthus annuus subjected to water deficit stress was evaluated. Results The water content of H. annuus shoots or roots didn’t change significantly by spraying with different concentrations of Nano- or Ord-TiO2. The dry mass (DM), relative dry mass (RDM) and root / shoot ratio of sunflower sprayed with Nano-TiO2, when averaged across all concentrations, mostly didn’t differ significantly from those sprayed with Ord-TiO2. In roots, the DM and RDM were decreased with increasing concentration of Ord-TiO2 but unchanged significantly by spraying with Nano-TiO2. Under all levels of water availability, total osmotic potential (ψs) and osmotic potential contributed by organic substances (ψorganic) didn’t change significantly by Ord-TiO2. Nano-TiO2 doesn't have any effect on the shoot or root dry mass and osmotic potential contributed by electrolytes (ψelect). Low concentrations of Nano-TiO2 significantly decreased relative water content (RWC) and ψs due to decreasing ψorganic. The ψs and ψelect of the root sap of sunflower were greatly lower than that of leaf sap. The soluble sugars partitioning and re-translocation was mainly in the priority of osmotic adjustment of the roots as a functional equilibrium under water deficit stress. Conclusion The foliar application of Nano-TiO2 didn’t significantly improve the sunflower water status built up by the shortage in water supply, and the quite small effect was via re-translocation of electrolytes and organic substances from shoots to roots.