The present investigation aimed to assess the allelopathic effects of aqueous leaf extracts of Datura stramonium L. (family: Solanaceae) on seed germination, hydroxyl radical (• OH), activities of some metabolic enzymes and antioxidants levels of both Trigonella foenum-graecum L. (fenugreek, family: Fabaceae)and Lepidium sativum L. (cress, family: Brassicaceae).The results revealed that Daturaaqueous leaf extract inhibited seed germination and retarded the activities ofthe following enzymes: glucose-6-phosphate dehydrogenase (G6PD, EC.1.1.1.49), 6-phosphogluconate dehydrogenase (6PGD, EC.1.1.1.44) and adenosine triphosphatase (ATPase, EC.3.6.1.3). However, Datura aqueous leaf extract enhanced NADH-oxidase (EC.1.6.3.1) activity in a concentration-dependent manner. Also, Datura leaf extract enhanced production of OH radical and antioxidants including proline, α-tocopherol and reduced glutathione (GSH) but decreased oxidized glutathione (GSSG) content.

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This study is aimed to investigate the activity of urease (EC 3.5.1.5, urea amidohydrolase) that catalyzes the hydrolysis of urea in 5-day-old Cucurbita pepo cotyledons subjected to various concentrations of different growth regulators. The treatment of C. pepo cotyledons with different concentrations (100-600 µmol) of different auxins [indole-3-acetic acid (IAA), indole butyric acid (IBA), indole propionic acid (IPA) and naphthalene acetic acid (NAA)]; or with different concentrations (100-300 µmol) of different cytokinins [kinetin, zeatin and benzyladenine (6-BA)] resulted in a significant increase of urease activity, compared to control. The optimal effects were recorded for each of 500 µmol of IAA and 300 µmol of zeatin treatments. A gradual increase in urease activity was detected in cotyledons treated with various concentrations (0.2-1.0 mM) of 28-homobrassinolide (HBL), in relative to control. A substantial increase in urease activity was observed in cotyledons subjected to different concentrations of triazole (10-60 mg L -1 ), containing either triadimefon (TDM) or hexaconazole (HEX), compared to control. The combination of 300 µmol zeatin with any of protein inhibitors, namely 5-fluorouridine (FUrd), cordycepin and α-amanitin, resulted in the alleviation of their inhibitory effect on the urease activity.

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