## 3 Results
However, compared with the Ca(NO\({}_{3}\))\({}_{2}\) treated alone, the concentrations of O\({}^{2-}\), H\({}_{2}\)O\({}_{2}\), MDA and the relative electrical conductivity of plant samples decreased by 30%, 16.7%, 36.9% and 28% with FA application, respectively (Figure 3c-f). This result suggested that FA could alleviate the oxidative damage induced by calcium nitrate stress. As shown in Figure 4, compared with the Con, the activities of SOD, POD, APX and CAT in Chinese flowering cabbage were enhanced to some degree by excess Ca(NO\({}_{3}\))\({}_{2}\), which increased by 37.5%, 69.64%, 33.33% and 27.27%, respectively (Figure 4). When treated with 100 \(\mu\)M FA, the reductase activities of SOD, POD, APX and CAT were further increased. That is, compared with Ca(NO\({}_{3}\))\({}_{2}\) treatment alone, the activities of SOD, POD, APX and CAT were observably increased by 8.3%, 9%, 18.2% and 6.7% with FA, which revealed that FA was able to strengthen the salt tolerance by improving the antioxidant ability of Chinese flowering cabbage. Figure 2: Effects of FA on photosynthetic parameters of Chinese flowering cabbage under Ca(NO\({}_{3}\))\({}_{2}\) stress. Measurements of (**a**) transpiration rate (_Tr_), (**b**) intercellular CO\({}_{2}\) concentration (_Ci_), (**c**) net photosynthetic rate (_Pn_) and (**d**) stomatal conductance (_Gs_) with different treatments. The indices were determined with three independent replicates of 10 plants each (n = 10). Different letters indicate a significant difference at \(p\leq\) 0.05. Figure 4: Effect of FA on the activities of SOD (**a**), POD (**b**), APX (**c**) and CAT (**d**) in Chinese flowering cabbage seedlings under Ca(NO\({}_{3}\))\({}_{2}\) stress. The plants cultivated in quarter-strength Hoagland’s solution with 15 mM Ca(NO\({}_{3}\))\({}_{2}\) were the control. Different letters indicate a significant difference at \(p\leq 0.05\). Figure 3: Effect of FA on histochemical localization and concentrations of ROS, MDA and relative electric conductivity in Chinese flowering cabbage under Ca(NO\({}_{3}\))\({}_{2}\) stress. The histochemical localization of O\({}^{2-}\) (**a**) and H\({}_{2}\)O\({}_{2}\) (**b**) in leaves. The accumulation of O\({}^{2-}\), (**c**), H\({}_{2}\)O\({}_{2}\) (**d**), MDA (**e**) and the relative electric conductivity (**f**) in leaves with different treatments. The plants cultivated in quarter-strength Hoagland’s solution with 15 mM Ca(NO\({}_{3}\))\({}_{2}\) were the control. Different letters indicated a significant difference at \(p\leq 0.05\). Root activity can directly affect the growth conditions of plants. Compared with Con, Ca(NO\({}_{3}\))\({}_{2}\) stress dramatically inhibited the root activity of Chinese flowering cabbage by 34.5%. However, the application of FA alleviated the inhibitory effect of Ca(NO\({}_{3}\))\({}_{2}\) stress on root activity. The root activity of Chinese flowering cabbage was increased by 24% with the FA+ Ca(NO\({}_{3}\))\({}_{2}\) octreatment (Figure 5). Effect of Exogenous FA on Nitrate Content, NO\({}^{3-}\)-N Ratio (Shoot: Root) and Nitrate-Related Enzyme Activity in Seedlings under Ca(NO\({}_{3}\))\({}_{2}\) Stress  
The nitrate content and ratio of NO\({}^{3-}\)-N (shoot/root) of Chinese flowering cabbage were determined (Figure 6). Compared with the Con, the nitrate contents of the shoots and roots were significantly increased by 55% and 105% with Ca(NO\({}_{3}\))\({}_{2}\) alone (Figure 6a). When cotreated with FA, the nitrate concentrations of roots and shoots were reduced by 27.7% and 12%, respectively (Figure 6a). In addition, Ca(NO\({}_{3}\))\({}_{2}\) + FA treatment could decrease the shoot-root translocation ratio of Ca(NO\({}_{3}\))\({}_{2}\), which could retain more Ca(NO\({}_{3}\))\({}_{2}\) in the root and protect the shoot growth of seedlings from nitrate toxicity (Figure 6b). It has been reported that the NRT1 gene family is involved in the absorption and transfer of nitrate [5]. Similarly, the transcriptional levels of _BCNRT1.1_ and _BCNRT1.5_ were studied.