FIGURE 5.

Overexpression of CAT2 suppresses the early senescence phenotype of nac075 mutant plants. (A) Leaf senescence phenotype of 32-day-old Col-0, nac075, nac075 CAT2ox, and CAT2ox plants. The scale bar represents 1 cm. (B) DAB and NBT staining were used to detect H₂O₂ and O⁻₂ accumulation, respectively, in the third or fourth leaves of Col-0, nac075, nac075 CAT2ox, and CAT2ox plants. The brown and blue color represent H₂O₂ and O⁻₂ accumulation, respectively. Scale bar, 1 cm. (C,D) Measurements of chlorophyll contents (C) and photochemical efficiency (Fv/Fm) (D) in Col-0, nac075, nac075 CAT2ox, and CAT2ox plants as leaves age. Data are represented as means ± SD, n = 3. The experiment was performed three times with similar results. Student’s t-test, ***P < 0.001. (E) A proposed model illustrates the transcription factor NAC075 that delays leaf senescence by deterring reactive oxygen species accumulation in Arabidopsis. NAC075 promotes CAT2 transcription by directly binding to its promoter, which is able to suppress ROS overproduction. Decreased ROS levels are capable of reducing programmed cell death, thereby delaying leaf senescence.