**3.6 Plant antioxidant defense against low temperature**

Low-temperature stress causes plants to activate their antioxidant defense appliance to counteract negative consequences. Cucumber (*C. sativus* cv. *Xinyan* 4) seedlings were open to low-temperature stress (15/8<sup>o</sup> C day/night) for the period of 8 days and reported that 3- and 2-fold increased Cu-ZnSOD and Fe-SOD activities, respectively, in response to increased H2O2 and O2**\*-**production [84]. Besides, after lowtemperature stress, *Cynodondactylon, Capsella bursa pastoris*, and *Citrus reticulata* showed considerably enhanced CAT activity [85–87]. Higher APX activity was seen in *Jatropha macrocarpa* in reaction to increase H2O2, which enhanced low-temperature

stress tolerance, but lower APX activity (>6-fold) in *J. curcas* was connected to enhanced sensitivity under low-temperature circumstances [88]. Cheng et al. [89] studied *Citrulluslanatus* by exposing low-temperature stress (10/5 0C, 7 days) and found that the antioxidant defence system was activated, with GSH/GSSG and AsA/ DHA ratios increasing considerably just a day after exposure in comparison to the control trial. Wang et al. [90] reported increased AsA and GSH levels in transgenic apple seedlings under low temperature stress in response to elevated H2O2 concentration (8o C, 12 hours). Han et al. [91] subjected 14-days old rice seedlings to low temperature (12o C, 6 days) stress and found increased H2O2 content and O2**\*-** accumulation, as well as enlarged SOD and CAT activity and also increased GSH/GSSG ratio.
