Thiourea induces antioxidant mechanisms of salt tolerance in flax plants

Salinity is one of the abiotic stress factors that affect plant physiology and cause various plant disorders. Thiourea, which consists of amino, thiol, and imino groups, is an antioxidant and growth regulator. The objective was to determine the antioxidant role of thiourea (0, 3, 6 mM) in attenuating the effects of salinity (0 mM, 50 mM, 100 mM NaCl) on growth, yield, and some biochemical compositions of flax (Linum usitatissimum L.) plants. Salt stress significantly reduced root and shoot length, root and shoot weight in dry and fresh matter, and yield components. In addition, salinity decreased photosynthetic pigments, total soluble sugar (TSS), and total free amino acids (TFAA) and suppressed ascorbate peroxidase (APX) and peroxidase (POX) activities, while proline and malondialdehyde (MDA) increased in stressed flax plants. Thiourea (TU) application improved all growth and yield characteristics of flax plants. TU increased photosynthetic pigment, APX, TSS, and TFAA while reducing proline and MDA. The differential accumulation of several proteins was reported under salt stress and TU-treatment. These proteins might be involved in the stress response and tolerance. Finally, foliar application of thiourea, especially at 6 mM, can counteract the effects of salinity on the growth and harvesting characteristics of flax plants by strengthening antioxidant defense mechanisms.