Herbicide-induced Activation of Glutathione S-transferase in Garlic (Allium sativum L.) Exposed to Oxadiazon

Herbicides are widely used in agriculture and may induce detoxification mechanisms in plants through activation of defense-related enzymes. Glutathione S-transferases (GSTs) play a crucial role in xenobiotic detoxification by conjugating toxic compounds with glutathione, thereby enhancing plant tolerance to chemical stress. The present study aimed to investigate the induction of GST activity in garlic (Allium sativum) following exposure to the herbicide oxadiazon and to compare the response among different plant species and tissues.

Garlic plants were treated with varying concentrations of oxadiazon [2-tert-butyl-4-(2,4-dichloro-5-isopropoxyphenyl)- 1,3,4-oxadiazol-5-one]. GST activity was measured in multiple plant tissues, including seedlings, roots, shoots, leaves and stems. Time-dependent enzyme activity was evaluated in eight-day-old plants after herbicide exposure. Comparative analyses were also conducted in shoots of broad bean (Vicia faba), corn (Zea mays), lentil (Lens esculenta), bitter vetch (Vicia ervilia), wheat (Triticum aestivum) and barley (Hordeum vulgare).

Oxadiazon treatment caused a progressive increase in GST activity in all examined garlic tissues. The lowest effective concentration inducing detectable enzyme activation was 0.025 ppm. Maximum GST activity exceeded 275% of control values at concentrations between 10 and 20 ppm. In eight-day-old garlic plants, GST activity in shoots increased significantly within 6 hours of exposure, reaching peak levels between 24 and 26 hours. Moderate increases in GST activity were observed in shoots of broad bean and corn, whereas lentil, bitter vetch, wheat and barley showed no significant enzymatic response following treatment. Oxadiazon effectively induces GST activity in garlic, demonstrating a species and tissue-specific detoxification response. The marked enhancement of GST activity suggests an adaptive biochemical mechanism contributing to herbicide tolerance in garlic and highlights GST as a potential biomarker for herbicide exposure in plants.