*2.2. Seed Priming and Germination Analysis*

Initially, rice seeds were dipped into the solution for sterilization with 5% (*w*/*v*) of NaClO for 20 min, then quickly splashed with purified water (ddH2O) to eradicate the remaining chloride. Secondly, these sterilized seeds were further primed by 0.01 mM SPM and water (H2O) separately at 30 ◦C in the dark for 24 h. Then, to restore the seed's original moisture levels, they were dried at ambient temperature. The seeds primed with water (H2O) were taken as controls. After priming, germination of seed assessment was conducted by using 50 seeds for each box (12 cm × 18 cm) with three repetitions for each treatment. Formerly, all germination boxes were retained inside a growth incubator with a fluctuating phase of 8 h light and 16 h of darkness at 25 ◦C for 14 days [26]. The chromium (0 and 100 μM) was applied to the incubated seeds. The Cr concentration was selected based on the preliminary experiments. The total seeds germinated, counted on the fifth day, were considered as the germination energy (GE) [26]. Furthermore, the total germinated seeds counted on day 14 were used for calculation of percentage of germination (GP), germination index (GI), vigor index (VI), and mean germination time (MGT), using the formulas used by Zheng [26].
