Assessment of the Biochemical Responses of Wheat Seedlings to Soil Drought after Application of Selective Herbicide

Abstract

Drought is a major environmental constrain with a deleterious effect on plant development leading to a considerable reduction of crop productivity worldwide. Wheat is a relatively drought tolerant crop during the vegetative stage. The herbicide Serrate^® (Syngenta) is a preparation containing two active chemical substances with different modes of action, which inhibit the biosynthesis of fatty and amino acids. It is commonly used as a systemic and selective chemical agent to control annual grass and broadleaf weeds in cereal crops and particularly in wheat, which is tolerant to Serrate^®. Seventeen-day-old wheat seedlings (Triticum aestivum L., cv. Sadovo-1) grown as soil culture under controlled conditions were sprayed with an aqueous solution of Serrate^®. Seventy-two hours later the plantlets were subjected to drought stress for seven days to reach a severe water deficit followed by four days of recovery with a normal irrigation regime. Oxidative stress markers, non-enzymatic, and enzymatic antioxidants were analyzed in the leaves of plants from the different treatment groups (herbicide-treated, droughts-stressed, and individuals which were consecutively subjected to both treatments) at 0, 96, and 168 h of drought stress, and after 96 h of recovery. Herbicide treatment did not alter substantially the phenotype and growth parameters of the above-ground plant parts. It provoked a moderate increase in phenolics, thiol-containing compounds, catalase, superoxide dismutase, glutathione reductase, and H₂O₂. However, significant variations of malondialdehyde, proline, and peroxidase activity caused by the sole application of the herbicide were not detected during the experimental period. Drought and herbicide + drought treatments caused significant growth inhibition, increased oxidative stress markers, and activation of enzymatic and non-enzymatic antioxidant defense reaching the highest levels at 168 h of stress. Plant growth was restored after 96 h of recovery and the levels of the monitored biochemical parameters showed a substantial decline. The herbicide provoked an extra load of oxidative stress-related biochemical components which did not aggravate the phenotypic and growth traits of plants subjected to drought, since they exhibited a good physiological status upon recovery.

Keywords: antioxidants; drought; herbicide; stress markers; wheat.

Figure 1

Phenotypic traits of wheat plants treated with herbicide and subjected to drought stress. (A) 96 h of drought, (B) 168 h of drought, (C) 96 h of recovery after restoring the normal irrigation regime, (D) 24 days of recovery.

Figure 2

Length (A), fresh weight (B), dry weight (C), water content (D) of above-ground part of wheat treated with herbicide and exposed to drought. Control values at 0 h: (A) 32.1 ± 0.4 cm; (B) 0.331 ± 0.011 g; (C) 0.041 ± 0.001 g; (D) 6.922 ± 0.061 g. The same letter means lack of statistical significance between treatments (n = 3, p < 0.05).

Figure 3

Content of malondialdehyde (A), free proline (B), and hydrogen peroxide (C) in leaves of wheat treated with herbicide and exposed to drought. Control values at 0 h: (A) 57.210 ± 4.104; (B) 0.837 ± 0.039; (C) 6.568 ± 0.696. The same letter means lack of statistical significance between treatments (n = 3, p < 0.05).

Figure 4

Activity of catalase (A), guaiacol peroxidase (B), superoxide dismutase (C), and glutathione reductase (D) in leaves of wheat treated with herbicide and exposed to drought. Control values at 0 h: (A) 0.211 ± 0.020; (B) 1.767 ± 0.192; (C) 60.280 ± 9.942; (D) 0.158 ± 0.012. The same letter means lack of statistical significance between treatments (n = 3, p < 0.05).

Figure 5

Content of total phenolics (A), and thiol groups containing compounds (B) in leaves of wheat treated with herbicide and exposed to drought. Control values at 0 h: (A) 4.557 ± 0.223; (B) 2.198 ± 0.115. The same letter means lack of statistical significance between treatments (n = 3, p < 0.05).