Calcium chloride and gibberellic acid protect linseed (Linum usitatissimum L.) from NaCl stress by inducing antioxidative defence system and osmoprotectant accumulation

Salinity stress affects many metabolic facets of plants and induces anatomical and morphological changes resulting in reduced growth and productivity. To overcome the damaging effects of salinity, different strategies of the application of nutrients with plant hormones are being adopted. The present study was carried out with an aim to find out whether application of calcium chloride (CaCl₂) and gibberellic acid (GA₃) could alleviate the detrimental effects of salinity stress on plant metabolism. Fifteen days old plants were supplied with (1) 0 mM NaCl + 0 mg CaCl₂ kg⁻¹ sand + 0 M GA₃ (control, T0); (2) 0 mM NaCl + 10 mg CaCl₂ kg⁻¹ sand + 0 M GA₃ (T1); (3) 0 mM NaCl + 0 mg CaCl₂ kg⁻¹ sand + 10⁻⁶ M GA₃ (T2); (4) 150 mM NaCl + 0 mg CaCl₂ kg⁻¹ sand + 0 M GA₃ (T3); (5) 150 mM NaCl + 10 mg CaCl₂ kg⁻¹ sand + 0 M GA₃ (T4); (6) 150 mM NaCl + 0 mg CaCl₂ kg⁻¹ sand + 10⁻⁶ M GA₃ (T5); (7) 150 mM NaCl + 10 mg CaCl₂ kg⁻¹ sand + 10⁻⁶ M GA₃ (T6). To assess the response of the crop to NaCl, CaCl₂ and GA₃, plants were uprooted randomly at 60 days after sowing. The presence of NaCl in the growth medium decreased all the growth and physio-biochemical parameters, except electrolyte leakage, proline (Pro) and glycine betaine (GB) content, thiobarbituric acid reactive substances (TBARS), H₂O₂ content, activities of superoxide dismutase (SOD) and catalase (CAT) and leaf Na content, which exhibited an increase of 37.6, 29.3, 366.9, 107.5, 59.1, 17.1, 28.4 and 255.2%, respectively, compared to the control plants. However, application of CaCl₂ in combination with GA₃ appears to confer greater osmoprotection by the additive role with NaCl in Pro and GB accumulation. Although the activities of antioxidant enzymes (SOD, CAT and POX) were increased by salt stress, the combined application of CaCl₂ and GA₃ to salt-stressed plants further enhanced the activities of these enzymes by 25.1, 6.7 and 47.8%, respectively, compared to plants grown with NaCl alone. The present study showed that application of CaCl₂ and GA₃ alone as well as in combination mitigated the adverse effect of salinity, but combined application of these treatments proved more effective in alleviating the adverse effects of NaCl stress.