Treatment of winter rye ( Secale cereale L.) seeds with thidiazuron mitigates the toxic response of seedlings to short-term treatment with a herbicide, paraquat

Winter rye ( Secale cereale L. cv. Rushnik) seeds were treated with thidiazuron (TDZ; 0.01–10 nmol/L), a plant growth regulator (PGR) with cytokinin-like activity, and grown hydroponically for 7 days. The aim of pretreatment with TDZ was to try and mitigate herbicide-induced stress in winter rye plants. The leaves of 7-days-old seedlings were sprayed with 100 μM of paraquat (PQ), a herbicide, and biochemical and physiological responses were assessed after 4 or 8 h in fully developed leaves. After 8 h, PQ treatment significantly increased H 2 O 2 and lipid peroxidation levels (39% increase for both relative to 0 h) as well as APOX activity (35% increase), but significantly decreased total antioxidant activity (33% decrease) and photosynthetic apparatus activity (up to 38% decrease), as assessed by chlorophyll fluorescence parameters. Pretreatment with TDZ weakened the toxic effects of PQ on rye seedlings, especially 8 h after PQ treatment. This was most evident for low doses (0.01 to 1 nmol/L) of TDZ. An index of efficiency indicated that 0.1 nmol/L TDZ was the most effective concentration to reduce the toxic effect of PQ on winter rye seedlings. This research provides fundamental information about the practical use of TDZ as a means to diminish the toxic effects of a herbicide (PQ) on cultivated winter rye plants.