FIGURE 2.

Effects of elevated CO₂ and heat stress either alone or combined on the photosynthetic apparatus and reactive oxygen species accumulation in tomato leaves. (A) the maximum photochemical efficiency of photosystem II (F_v/F_m) shown in pseudo color images, the false color code depicted in the image ranges from 0 (black) to 1 (purple); (B) F_v/F_m values; and (C) in situ accumulation of superoxide (${\text{O}}_2^{\mathrm{•-}}$) and hydrogen peroxide (H₂O₂) by NBT and DAB staining in tomato leaves. Tomato seedlings kept at ambient (380 μmol mol^-1) and elevated CO₂ concentration (800 μmol mol^-1) were challenged with a 24 h heat stress (42°C temperature) and then allowed to recover for 24 h. F_v/F_m was measured on the third fully expanded leaves after 30 min of dark adaptation using an imaging pulse amplitude modulated (PAM) fluorimeter (IMAG-MAXI; Heinz Walz, Effeltrich, Germany). The results are expressed as the mean values ± SD, n = 6. Different letters above the bars in (B) indicate significant differences at P < 0.05 according to Tukey’s test.