## 3 Results
### Coordinated Antioxidant Defense Systems in LT-Tolerant Accession  
Plant tends to ameliorate the cellular oxidative stress by promoting the activity of antioxidant defense system. We profiled activities of antioxidant defense systems in Jing72464 and JingX201 under NT and LT conditions. Activity of SOD shown no difference between two inbred lines (\(p=0.946\)), while activity of CAT was slightly higher (13.9%) in Jing72464 than that of JingX201 (\(p=0.013\)) (Figure S1). Among the four antioxidant enzymes in AsA-GSH pathway, activities of GR and MDHAR showed no difference between the  
Figure 1: Germination rate of different elite maize inbred accessions under low temperature (**a**) Daily average temperature (green line) from 20 March to 20 June in the field where experiment conducted. The color-filled zone indicated the duration time after sowing when 5 percent coleoptile of Jing72464 emerged from the soil. Blue color zone indicated low temperature (LT) condition that seeds were sowing in early spring, while brown color zone indicated normal temperature (NT) condition that seeds were sowing in summer. (**b**) Germination rate of 6 maize inbred accessions in the filed condition under LT or NT. Data represent mean values of three independent replicate (\(n>1000\)). (**c**) Inhibition rate of LT on seed germination. Inhibition rate was calculated as the germination rate in LT versus that in NT. Significant differences in (**b**,**c**) were labeled with different Roman (a, b, c) or Greek letters (\(\alpha\), \(\beta\), \(\gamma\)). two inbred lines (Figure S1). APX, functions as a key enzyme in the fine control of H\({}_{2}\)O\({}_{2}\), showed 34% higher activity in Jing72464 than that of JingX201 (\(p<0.001\)) (Figure 4a). DHAR, function in the direction of DHA consuming with the help of GSH, showed 54% reduced activity in Jing72464 when compared with JingX201(\(p<0.001\)) (Figure 4b). Among the nonenzymatic antioxidants in AsA-GSH pathway, no difference in the AsA content was observed between Jing72464 and JingX201 (\(p=0.298\)). However, DHA content was significantly higher (53.6%) in Jing72464 than that of JingX201 (\(p<0.001\)) (Figure 4c,d). Consistently, the GSH content in Jing72464 was slightly higher (32%) than that of JingX201, whereas GSSG (oxidized form of GSH) content was more than 1.2-fold higher (121.7%) in Jing72464 than that of JingX201 (\(p<0.001\)) (Figure 4f,g). This result implied that activities of APX and DHAR is not only associated with the antioxidants level of AsA and GSH, but also with the content of oxidative substrate of these two antioxidants. As the result, pool size of total ascorbate (AsA + DHA) was 23% higher in LT-tolerant inbred Jing72464 than LT-sensitive inbred JingX201 (Figure 4e). Similarly, pool size of total glutathione (GSH + GSSG) was 38% higher in Jing72464 than JingX201 (\(p<0.001\)) (Figure 4h). The AsA/ DHA and GSH/GSSG ratios were 40.8% and 40.6% lower in Jing72464, respectively (Figure 4i,j). Figure 2: Variation in seedling establishment among maize accessions under low temperature. (**a**) Plant morphology of seedlings with the first true leaf expanded. Scale bar, 2 cm. (**b**) Plant height of 6 maize inbred accessions in the filed condition under LT or NT. Data represent mean values of three independent replicate (\(n>12\)). (**c**) Inhibition rate of LT on plant height. Data were calculated as the plant height in LT versus the means in NT. (\(n>12\)). (**d**) Chlorophylll content of 6 maize inbred accessions in the filed condition under LT or NT. Data are mean \(\pm\) s.e.m. (\(n=10\)). (**b–d**) Significant differences were labeled with different Roman (a, b, c) or Greek letters (\(\alpha\), \(\beta\), \(\gamma\)). Figure 4: Enhanced GSH-AsA redox status in LT-tolerant accession Jing/72464. (**a**,**b**) Cellular activity of ascorbate peroxidase (**a**) and dehydroroscorbate reductase (**b**) in LT-sensitive inbred JingX201 and LT-tolerant inbred Jing/72464 under NT and LT condition. (**c**,**d**) Cellular contents of AsA (**c**) and DHA (**d**).