Influence of ZnO Nanoparticles on Early Growth Stage of Fragrant Rice at Low Temperature (LT) Stress

Foliar application of ZnO Nanoparticles (ZnO-NPs) could reduce adverse effects of multiple abiotic stresses in crop plants. The present study was conducted to induce the low temperature stress tolerance in growing rice plants by the foliar application of ZnO-NPs. Two fragrant rice cultivars i.e., Meixiangzhan2 and Xiangyaxiangzhan were grown under normal temperature (NT, day/night: 28℃/25℃) and low temperature (LT, day/night: 15℃/12℃) after foliar application of Zn and ZnO-NPs with following treatments viz., application of distilled water only (CK), ZnSO₄·7H₂O at 6.6 mg·L ⁻¹ (CK1), and application of ZnO-NPs at 25, 50, 100, and 200 mg·L⁻¹ regarded as N25, N50, N100, and N200, respectively. The growth and physiological attributes were examined to assess the potential of ZnO-NPs to induce low temperature stress tolerance in growing rice plants. The ZnO-NPs, and temperature × ZnO-NPs had a significant effect on the growth and physiological attributes (p < 0.05) of rice seedlings. The ZnO-NPs application enhanced the root dry weight, root-shoot ratio, total dry weight, and chlorophyll a/b ratio in Xiangyaxiangzhan by 10.48%-18.10%, 1.96%-20.31%, 3.25%-6.02%, and 3.70%-6.11% at low temperature, respectively. The activity of antioxidant enzymes in Meixiangzhan 2 was increased, whilst the malondialdehyde (MDA) content in root was significantly declined. Moreover, lower levels of ZnO-NPs treatment regulated the activity of N-metabolizing enzymes i.e., nitrate reductase (NR), glutamate synthase (GS), glutamine oxoglutarate aminotransferase (GOGAT) and in seedlings under low temperature. Regarding correlation analysis, the N100 and N200 treatment exhibited a stronger correlation with growth-related attributes, compared to other treatments. Foliar application of ZnO-NPs at appropriate concentration (100 mg·L⁻¹) could alleviate the inhibitory effect of low temperature stress on the early growth of fragrant rice.