Seed nano-priming with potassium silicate and zinc oxide mitigates drought stress by modulating metabolic homeostasis and forage yield in Sorghum genotypes

Drought stress triggers various physiological and biochemical responses in plants, and osmotic regulation is a key mechanism for maintaining cell turgor under water deficiency. Nano-priming is an emerging strategy to enhance plant resilience. This study examined the effects of seed nano-priming using nano potassium silicate (K 2 SiO 3 ) and nano zinc oxide (ZnO) at a concentration of 250 mg L - ¹ on three forage Sorghum varieties, namely Pegah, Speedfeed, and Pejpal, under drought conditions. A split-plot factorial experiment was conducted employing a randomized complete block design with three replicates ( n = 3). Irrigation levels [100%, 75%, and 50% of field capacity (FC)] served as the main plot factor, while seed treatments (control, hydropriming, nano-K 2 SiO 3 , and nano-ZnO) and varieties were assigned to subplots. Results showed that several physiological parameters were enhanced to promote drought tolerance: the highest fresh and dry forage yields (103.12 and 20.99 t/ha, respectively) were obtained in Zarghan with nano-ZnO treatment. Nano-priming significantly enhanced photosynthetic pigments, achieving maximum chlorophyll a and b contents (32.91 and 13.82 mg/g FW, respectively) in Zarghan. Under severe drought (50% FC), the Pejpal variety exhibited superior resilience by maintaining the highest proline accumulation (1 mg/g FW) and antioxidant activities (POD: 15.19; SOD: 0.17 U/mg protein). Hierarchical clustering and PCA confirmed that proline and antioxidant enzymes formed a distinct subcluster, serving as dual osmolyte and stress-defense markers. Nano-priming modulated these enzymatic responses and mitigated the accumulation of reactive oxygen species (ROS). Principal Component Analysis (PCA) and Heatmap correlation results further confirmed that nano-ZnO effectively reconfigured the physiological profile of Sorghum to maintain metabolic homeostasis under severe water deficit. Nano-priming with nano-ZnO and nano-K 2 SiO 3 improved drought tolerance and forage yield in Sorghum, with nano-ZnO showing superior performance. This approach offers a promising way to enhance crop resilience in water-limited environments.