Figure 3.

Exogenous application of selenium protected the photosynthetic apparatus and alleviated the oxidative stress induced by cold stress. (A) Ultrastructures of cells of cucumber seedlings leaf of control, selenium application, cold stress, and selenium application under cold stress. Red arrow points to starch grain, blue arrow points to osmiophilic granule. (B) ${\text{O}}_2^{-}$ in leaves was detected by NBT staining. (C) The activity levels of SOD, POD, CAT, and APX of control, selenium application, cold stress, and selenium application under cold stress with 5 and 10 days treatments, respectively. Values are expressed as means of three replicates ± SD, and different letters are significantly different (P < 0.05).