Photosynthesis, Chlorophyll Fluorescence, and Hormone Regulation in Tomato Exposed to Mechanical Wounding

Abstract

To understand the physiological responses of seedlings to mechanical wounding, we analyzed photosynthesis, chlorophyll fluorescence, and endogenous hormones in tomato (Solanum lycopersicum L.) subjected to varying levels of mechanical pressure. The results showed that, at 4 h after wounding, excess excitation energy was dissipated as thermal energy through the reduction in the photosystem II (PSII) opening degree and the increase in non-photochemical quenching. Photodamage was avoided, and stomatal closure was the most prominent factor in photosynthesis inhibition. However, 12 h after wounding, the photoprotective mechanism was insufficient to mitigate the excess excitation energy caused by the wound, leading to photochemical damage to physiological processes. Meanwhile, the non-stomatal factor became the most prominent limiting factor for photosynthesis at 80 N pressure. At 12 and 36 h after wounding, the concentrations of abscisic acid (ABA), methyl jasmonate (MeJA), indole-3-acetic acid (IAA), zeatin riboside (ZR), and gibberellic acid (GA₃) in the stems showed a trend towards being increased, which promoted wound healing. However, after mechanical wounding, the ratio of stress- to growth-promoting hormones first increased and then decreased. This pattern can enhance stress resistance and promote cell division, respectively. Comprehensive analysis showed that the fluorescence parameter, photochemical quenching coefficient (Qp_Lss), was the most suitable indicator for evaluating mechanical wounding conditions.

Keywords: PSII efficiency; hormonal crosstalk; mechanical wounding; photosynthetic limiting factors; principle component analysis.

Figure 1

The schematic diagram of the experimental design.

Figure 2

Changes in (A) photosynthetic rate (P_n), (B) stomatal conductance (g_s), (C) transpiration rates (T_r), and (D) internal CO₂ concentrations (C_i) of Solanum lycopersicum L. under non-wounding and wounding conditions. Values are averages of 5 replicates ± s.e. Different letters refer to significant differences among treatments.

Figure 3

Changes in (A) minimum fluorescence (F_o), (B) maximum fluorescence (F_m), and (C) variable fluorescence (F_v) of Solanum lycopersicum L. under non-wounding and wounding conditions. Values are averages of 5 replicates ± s.e. Different letters refer to significant differences among treatments.

Figure 3

Changes in (A) minimum fluorescence (F_o), (B) maximum fluorescence (F_m), and (C) variable fluorescence (F_v) of Solanum lycopersicum L. under non-wounding and wounding conditions. Values are averages of 5 replicates ± s.e. Different letters refer to significant differences among treatments.

Figure 4

Changes in (A) maximal photochemical efficiency (F_v/F_m), (B) potential activity of PSII (F_v/F_o), (C) photochemical quenching coefficient (QP_L_ss), and (D) steady-state non-photochemical quenching (NPQ_L_ss) of Solanum lycopersicum L. under non-wounding and wounding conditions. Values are averages of 5 replicates ± s.e. Different letters refer to significant differences among treatments.

Figure 5

Changes in (A) stem abscisic acid (ABA), (B) stem methyl jasmonate (MeJA), (C) stem indole-3-acetic acid (IAA), (D) stem zeatin-riboside (ZR), and (E) stem gibberellic acid (GA₃) of Solanum lycopersicum L. under non-wounding and wounding conditions. Values are averages of 5 replicates ± s.e. Different letters refer to significant differences among treatments.

Figure 6

Changes in (A) stem ABA/IAA, (B) stem MeJA/IAA, (C) stem ABA/ZR, (D) stem MeJA/ZR, (E) stem ABA/GA₃, and (F) stem MeJA/GA₃, stem ABA/GA₃, and stem MeJA/GA₃ of Solanum lycopersicum L. under non-wounding and wounding conditions. Values are averages of 5 replicates ± s.e. Different letters refer to significant differences among treatments.

Figure 7

Principal component analysis (PCA) of physiological parameters in Solanum lycopersicum L. at 4 h (black), 12 h (red) and 36 h (green) after 0 N (triangle), 40 N (circle), and 80 N (square) mechanical pressures of wounding.