Unfolding the role of silicon dioxide nanoparticles (SiO2NPs) in inducing drought stress tolerance in Hordeum vulgare through modulation of root metabolic, nutritional, and hormonal profiles

Drought, a serious global issue and a threat to sustainable agriculture, causing crop inhabitation and hindering agricultural growth and development. Metal oxide nanoparticles (NPs) are essential for growth and development of plants in the face of abiotic stressors. The present study investigated the impact of silicon dioxide nanoparticles (SiO₂NPs) at the rate of 10 mg/L and 20 mg/L taken as (1-SiO₂NPs and 2-SiO₂NPs, respectively) on the morphological, nutritional, biochemical, hormonal, and the changes in metabolites alterations and/or modifications in Hordeum vulgare roots under three different levels of drought stress [75, 50, and 25 % filed capacity (FC)]. Furthermore, we tested hypothesis that i) drought stress affect the specific transporter proteins named NRT1, AMT1, PHT1, and HKT1 in barley roots causes nutritional imbalance, ii) SiO₂NPs application reduce the osmotic stress and nutritional imbalance improve the barley's overall growth, iii) N-R-T transporters work in collaboration with the growth hormones helps drought sensitive barley roots. The current results suggested that maximum damage to barley roots was occurred at 50 and 25 % FC while the exogenous 2-SiO₂NPs application substantially improved the biochemical processes, and metabolic activities, alleviated the oxidative stress by substantially reducing H₂O₂, OH^-, and MDA by 9, 12, and 17 % significantly enhanced the nutritional content including K⁺, NO₃^-, NH₄⁺, and P up to 1.4-, 1.1-, 1.3-, and 1.5-fold of the barley roots under severe drought condition (25 % FC). The results also indicated that the nutrient transporters work in conjugation with the growth hormones such as tZR, tZ, and cZ showed an up-regulation of 97.9-, 8-, and 1.1-fold, whereas, ABA and JA derivatives showed an increment of 1.1-, 1.4-, 1.2-, and 1.4-fold (ABA, ABA-GE, JA, JA-Me), while the others e.g. IAA, IAA-Glu, IAA-GE, SA, GA3, and GA4 showed a slight reduction of 6, 24, 21, 6, 6, and 4 % under severe (25 % FC) water-deficit condition, respectively. Another finding of this research revealed that drought stress substantially reduced the Total Pro. content up to 12 and 20 % under both 50 and 25 % FC, while NRT1, AMT1, and PHT1 showed an inhabitation of 14, 20, and 15 % under moderate drought (50 % FC) whereas (26, 34, and 33 %) under severe drought conditions in Hordeum vulgare roots, respectively. On the other hand, HKT1 experienced a substantial rise (1.23- and 1.45-fold) under both the water stress conditions. Interestingly, SiO₂NPs application (20mg/L) ameliorated the negative effects of droughts and restored the nutrients transporter proteins in barley roots.