Phytochemical and physiological changes in Salvia officinalis L. under different irrigation regimes by exogenous applications of putrescine

Water stress is the major factor limiting plant productivity and quality in most regions of the world. In the present study, a two-year field experiment was conducted to determine the influence of putrescine (Put) on phytochemical, physiological, and growth parameters of Salvia officinalis L. under different irrigation regimes. The highest stem dry weight (56.05 and 65.21 g m−2) plus leaf dry weight (124.51 g m−2) were predicted in irrigation regimes of (20 and 40%) plus 20% available soil water was depleted (ASWD), respectively. Total phenolic content (TPC) was increased significantly under the irrigation regime of 80% with the application of distilled water in spring. TPC showed an increasing trend with increases in Put concentration under all irrigation regimes in both spring and summer. The highest total flavonoids content (TFC) in wavelengths of 415 and 367 nm were predicted in 2.25 mM Put. The highest ascorbate peroxidase (APX) activity (0.13 μmol mg−1 protein) was predicted in the irrigation regime of 20% with the application of distilled water in spring and summer. There was a significantly negative correlation coefficient between APX, TPC, and TFC. Indeed, there was a decreasing trend in APX and an increasing trend in TPC and TFC with increases in Put concentration under the irrigation regime of 20% ASWD. The highest hydroxyl radical scavenging activity (HRSA) values were obtained under irrigation regimes of 49.27% and 20% ASWD in spring and summer, respectively. There was an increasing trend in endogenous Put with increases in the Put concentration. The responses of compatible osmolytes to irrigation regime can be expressed by quadratic model, suggesting maximum proline (0.52 mg g−1), total reducing sugars (TRS) (0.37 mg g−1), xylose (0.68 mg g−1), and mannose (0.37 mg g−1) values would be obtained in irrigation regimes of 68.33%, 48.33%, 53.75%, and 56.25% ASWD, respectively.