Figure 6.

Response mechanisms underlying resistance to low-temperature stress in maize seedlings. The traits included chlorophyll level, i.e., chlorophyll a content (Chl a), chlorophyll b content (Chl b), chlorophyll a+b content (Chl a+b), chlorophyll a:b ratio (Chl a/b); photosynthetic performance, i.e., net photosynthetic rate (Pn), intercellular CO₂ concentration (Ci), stomatal conductance (Gs), transpiration rate (Tr), water use efficiency (WUE), ribulose 1,5–biphosphate carboxylase activity (Rubisco); antioxidant enzymes system, i.e., superoxide dismutase activity (SOD), peroxidase activity (POD), catalase activity (CAT), ascorbate peroxidase activity (APX); reactive oxygen species (ROS) level, i.e., O₂^•− production rate (O₂^•−), H₂O₂ content (H₂O₂), membrane system, malondialdehyde content (MDA), membrane stability index (MSI); osmotic adjustment ability, i.e., proline content (Pro); and polyamines (PAs) metabolism, i.e., putrescine concentration (Put), spermidine concentration (Spd), and spermine concentration (Spm). The red and green arrow indicated that the corresponding traits were increased and decreased under low-temperature treatment, respectively. “+ +” and “− −” indicated that the corresponding pathways acted positively and negatively, respectively.