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

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 (<i>Zea mays</i>), 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 <i>a</i> fluorescence due to the application of 3-cyanobenzoic acid, indicating compromised photosynthetic activity. Parameters such as the chlorophyll index, net assimilation (<i>A</i>), stomatal conductance (<i>g</i>_s), intercellular CO₂ concentration (<i>C</i>_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 <i>A</i>/PAR curve revealed reductions in the maximum net assimilation rate (<i>A</i>_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 (<i>J</i>), and mesophilic conductance (<i>g</i>_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.