Assessment of 3-Cyanobenzoic Acid as a Possible Herbicide Candidate: Effects on Maize Growth and Photosynthesis

Abstract

Chemical weed control is a significant agricultural concern, and reliance on a limited range of herbicide action modes has increased resistant weed species, many of which use C4 metabolism. As a result, the identification of novel herbicidal agents with low toxicity targeting C4 plants becomes imperative. An assessment was conducted on the impact of 3-cyanobenzoic acid on the growth and photosynthetic processes of maize (Zea mays), a representative C4 plant, cultivated hydroponically over 14 days. The results showed a significant reduction in plant growth and notable disruptions in gas exchange and chlorophyll a fluorescence due to the application of 3-cyanobenzoic acid, indicating compromised photosynthetic activity. Parameters such as the chlorophyll index, net assimilation (A), stomatal conductance (g_s), intercellular CO₂ concentration (C_i), maximum effective photochemical efficiency (F_v'/F_m'), photochemical quenching coefficient (q_P), quantum yield of photosystem II photochemistry (ϕ_PSII), and electron transport rate through PSII (ETR) all decreased. The A/PAR curve revealed reductions in the maximum net assimilation rate (A_max) and apparent quantum yield (ϕ), alongside an increased light compensation point (LCP). Moreover, 3-cyanobenzoic acid significantly decreased the carboxylation rates of RuBisCo (V_cmax) and PEPCase (V_pmax), electron transport rate (J), and mesophilic conductance (g_m). Overall, 3-cyanobenzoic acid induced substantial changes in plant growth, carboxylative processes, and photochemical activities. The treated plants also exhibited heightened susceptibility to intense light conditions, indicating a significant and potentially adverse impact on their physiological functions. These findings suggest that 3-cyanobenzoic acid or its analogs could be promising for future research targeting photosynthesis.

Keywords: chlorophyll a fluorescence; enzyme inhibitor; gas exchange; phenolics; phytotoxicity; pyruvate O-phosphate dikinase; weeds.

Figure 1

Hydroponically grown maize plants treated with 3-cyanobenzoic acid for 14 days: 0 mM (A), 0.5 mM (B), and 1.0 mM (C). Scale bars represent 10 cm.

Figure 2

Effects of 3-cyanobenzoic acid on hydroponically grown maize plants for 14 days. Parameters measured include (A) chlorophyll content (SPAD index), (B) maximum quantum efficiency of PSII photochemistry (F_v/F_m), (C) net assimilation (A), (D) stomatal conductance (g_s), (E) intercellular CO₂ concentration (C_i), (F) maximum efficiency of PSII (F_v′/F_m′), (G) non-photochemical quenching (NPQ), and (H) photochemical quenching (q_P). Means values (n = 16–22 ± SEM) significantly different from the control are marked with * p ≤ 0.05, ** p ≤ 0.01, according to Dunnett’s test.

Figure 3

Effects of 3-cyanobenzoic acid on hydroponically grown maize plants for 14 days on quantum yield of photosystem II photochemistry (ϕ_PSII) (A) and electron transport rate through PSII (ETR) (B). Means (n = 22 ± SEM) marked with * or ** are statistically different from the control according to Dunnett’s test at 5% and 1% significance levels, respectively.

Figure 4

Average net assimilation (A) curves in response to varying photosynthetically active radiation (PAR) for maize plants grown hydroponically with 3-cyanobenzoic acid for 14 days. The initial linear region of the graph is magnified for clarity. Data are presented as mean values (n = 4).

Figure 5

Effects of 3-cyanobenzoic acid on hydroponically grown maize plants after 14 days, focusing on parameters derived from the A/PAR curve: (A) net assimilation (A_max), (B) apparent quantum yield (ϕ), (C) light compensation point (LCP), and (D) dark respiration rate (R_D). Means values (n = 3–4 ± SEM) significantly different from the control are marked with, ** p ≤ 0.01, according to Dunnett’s test.

Figure 6

Average net assimilation (A) curves in response to varying intercellular CO₂ concentration (C_i) forma maize plants grown hydroponically with 3-cyanobenzoic acid for 14 days. Data are presented as mean values (n = 4–6).

Figure 7

Effects of 3-cyanobenzoic acid on maize plants grown hydroponically for 14 days, focusing on parameters derived from the A/C_i curve: (A) maximum carboxylation rate of RuBisCo (V_cmax), (B) maximum carboxylation rate of PEPCase (V_pmax), (C) rate of photosynthetic electron transport (J), and (D) mesophyll conductance (g_m). Means values (n = 4–6 ± SEM) significantly different from the control are marked with * p ≤ 0.05, ** p ≤ 0.01, according to Dunnett’s test.

Figure 8

Chlorophyll a fluorescence OJIP transient curves in maize plants grown hydroponically with 3-cyanobenzoic acid for 14 days. The OJIP curve represents key fluorescence intensities: the minimal fluorescence when all PSII reaction centers are open (O step), the intensity at 0.002 s (J step), the intensity at 0.03 s (I step), and the maximal fluorescence when all PSII reaction centers are closed (P step, at 0.3 s). Data are presented as means (n = 18 ± SEM).

Figure 9

Effects of 3-cyanobenzoic acid on specific energy flux parameters in hydroponically grown maize plants after 14 days of treatment. Parameters include: absorption flux per reaction center (ABS/RC), energy trapping per reaction center (TR₀/RC), electron transport per reaction center (ET₀/RC), energy dissipation per reaction center (DI₀/RC), reaction center density per cross-sectional area (RC/CS), quantum yield of primary PSII photochemistry (TR₀/ABS), efficiency with which a trapped electron is transferred from Q_A to Q_B (ET₀/TR₀), quantum yield of electron transport from Q_A to Q_B (ET₀/ABS), and performance indices (PI_ABS and PI_Total). Data are presented as means (n = 18 ± SEM). Mean value significantly different from the control is marked with * p ≤ 0.05, according to Dunnett’s test.