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Herbicides are used in agriculture to increase crop yield. However, their use often prompts concern about the consequences safety of crop production. Salicylic acid (SA) is a phenolic compound considered a phytohormone that confers plant resistance to different stresses. To determine the influence of SA on the reduction of herbicide-induced toxicity, we used young bean (Phaseolus vulgarisL.) seedlings treated with 1 mM of SA, 100 µM of prometryne or combined treatments. After 30 days of culture, prometryne treatment resulted in plant growth inhibition (shoot height, leaf area, fresh and dry weight) and decreased photosynthetic pigments content. It increased malondialdehyde (MDA) and hydrogen peroxide (H2O2) levels. Meanwhile, the activities of enzymatic antioxidants, catalase (CAT) and ascorbate peroxidase (APX), as well as herbicide detoxification enzyme glutathione S‑transferase (GST), were significantly improved. Furthermore, herbicide enhanced proline amount and decreased that of glutathione. These findings reflect the presence of stress status. An exogenous supply of SA seemed to reduce the deleterious effects caused by prometryne and appeared to overcome this stress status. Such positive effect was reflected by enhancement of growth and leaf pigments contents, regulating antioxidant enzyme activities (CAT, APX, GST), and decreasing oxidative stress indices. This study demonstrates that exogenous application of SA to young bean plants reversed and/or minimized the damage caused by prometryne through the protection and improvement of some morpho-biochemical characters.

Ascorbate (vitamin C), a major antioxidant in plants, significantly mitigates cellular reactive oxygen species (ROS) accumulation caused by many abiotic stresses such as herbicides. This study examined the protection by ascorbate of a medicinal plant, fenugreek (Trigonella foenum-graecumL.), from oxidative stress induced by paraquat herbicide. Fenugreek was irrigated with 50 mM of ascorbate solution before herbicide treatment at 100 µM. The effects of both treatments were assessed at the physiological and biochemical level by evaluating: shoot and root dry weight, total chlorophyll, malondialdehyde (MDA), proline, and hydrogen peroxide (H2O2) contents, and reactive oxygen detoxifying enzymes. Results showed that paraquat treatment provoked a set of damages in plants. The total chlorophyll content was diminished, fenugreek shoot and root dry weights were retarded, and the contents of proline, MDA, and H2O2were increased. When ascorbate was combined with paraquat, it reduced the proline, MDA, and H2O2contents, fenugreek shoot, root dry weight and catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) activities which were significantly different compared to that noted after paraquat applications. The results conclude that paraquat induces oxidative stress and that ascorbate treatment before herbicide prevents ROS accumulation in plant cells, elicits antioxidative responses, and repairs damages in fenugreek seedlings.

The present study was performed to verify that the exogenous application of proline as an antioxidant can effectively reduce the damage of the herbicide Basagran® on fenugreek (Trigonella foenum-graecum). Sterilized healthy seeds were soaked in proline (7 mM) with or without the herbicide Basagran® (10–4M) applied as a foliar spray. Performance was evaluated based on the plant’s physiological and biochemical attributes. Results revealed that herbicide stress caused seedling growth inhibition, which could be due to hydrogen peroxide (H2O2) accumulation with an increase in malondialdehyde (MDA) level and electrolyte leakage (EL). As a consequence, proline metabolism was affected, including the activity of proline dehydrogenase (PRODH) and pyrroline-5-carboxylate synthetase (P5CS), and levels of pyrroline-5-carboxylate (P5C) and proline (Pro) as well as glutathione (GSH) level, total antioxidant capacity (TAC), and activity of catalase (CAT) and glutathione-s-transferase (GST) were affirmatively influenced. However, the exogenous application of proline attenuated the harmful effects of Basagran® by improving growth performance, which might be related to enhanced antioxidant activities, total chlorophyll, relative water content (RWC), and GSH levels. Proline treatment also reduced the damage caused by increased MDA levels and reactive oxygen species (ROS) by regulating the enzymatic and non-enzymatic defense systems. Principal component analysis showed that increased oxidative damage and water imbalance were the most important contributors to herbicide stress-induced damage; however, the proline-mediated antioxidant defense was the crucial determinant of herbicide tolerance in fenugreek. Collectively, findings obtained from this study revealed that externally used proline protects against herbicide stress by enhancing cellular defense mechanisms. These results indicate the capacity of proline to improve the tolerance of fenugreek plants subjected to herbicide constraints.