Cysteine and thiourea represent natural antioxidants (compounds containing sulfur) that can protect plants against a broad spectrum of environmental stresses. A field trial directly assessed the probable influence of foliar treatment of cysteine (50, 75, and 100 mg L^-1) and thiourea (200, 400, and 600 mg L^-1) on growth parameters, photosynthetic pigments, seed yield quantity and quality, and some biochemical characteristics of flax plants grown in sandy soil. A foliar spray of cysteine and thiourea markedly increased growth characters, concurrently with an increase in Indole acetic acid content and photosynthetic pigments. Compatible osmolytes and yield components also improved compared with untreated plants. All treatments increased seed yield, oil content, and its components. The ratio of unsaturated fatty acids to saturated fatty acids bore enrichment in the yielded seeds. It was also noticeable that the 400 mg L^-1 thiourea was the most pronounced in increasing to maximum the tested parameters of the flax plant. It could be a conclusion that foliar sprays of cysteine and thiourea were active in ameliorating flax performance through increasing antioxidant compounds and enzymes.

Keywords: Flax, cysteine, thiourea, growth, osmoprotectant, antioxidants, yield, fatty acids

Key findings: The flax seed variety (Sakha-3) exhibited its maximum growth and yield by foliar spraying with 400 mg L^-1 thiourea or 75 mg L^-1 cysteine when cultivated in sandy soils, and this effect came as a response to improving the antioxidant defense system.