Evaluation of the Biochemical Reaction of Sunflower Seedlings to Selenium Levels in Saline Conditions

 Background and Objectives :

Salinity is one of the detrimental environmental factors that limit the productivity of crop plants worldwide. Most of the crop plants are sensitive to salinity. Selenium (Se) has not been classified as a plant essential element, but its role as a beneficial element and its ability in amelioration of different environmental stresses has been reported in different plant species. The aim of this study was to investigate the effects of Se on sunflower plants under salt stress conditions.

  Materials and Methods:

 The experiment was conducted as factorial in a completely randomized design by three replications in a hydroponic system with a temperature regime of 25/18°C, photoperiod of 14 h, and relative humidity of 70% in a growth chamber. Seeds were germinated in petri-dishes and then uniform 3-day old seedlings were transferred to 50% Hoagland solution. One week after pretreatment, plants were transferred to 100% Hoagland solution and treated with selenium) sodium selenate; 0, 5, and 10 µM) and salinity (sodium chloride; 50 and 100 mM) for two weeks. Plant's shoots were harvested 15 days after treatments, and frozen in liquid nitrogen until assays.  

Results:

 The results indicated that salinity at both levels significantly increased the MDA as well as free phenol and decreased the flavonoids contents of plants. The anthocyanin, soluble sugars, and total protein contents and the activity of APX increased significantly in response to 50 mM of NaCl, while the proline, tannins, and lignin contents increased, but dry weight and height of shoot decreased significantly in response to 100 mM of NaCl. In non-saline condition, Se application at 5 µM decreased the flavonoids and lignin contents and increased the free phenols, shoot height, and POD activity significantly. Application of Se at 10 µM in non-saline conditions significantly increased the lignin and MDA contents and APX activity. In saline condition with 50 mM of NaCl, Se application at both two levels decreased the soluble sugars and APX activity, and at 10 µM decreased the lignin and increased the tannin contents significantly. In saline condition with 100 mM of NaCl, Se application at both two concentrations considerably decreased the proline, lignin, and tannin contents but increased the APX activity. Furthermore, a reduction in soluble sugars by application of 5 µM of Se was seen in plants that were in saline conditions with 100 mM of NaCl.  

Discussion:

 According to the results of this study, salinity induced oxidative stress in sunflower, especially at 100 mM that was obvious by elevated level of MDA. Even though the Se application in saline condition could induce the notable changes in the phenolic compounds and promoted the activity of APX, it could not inhibit the MDA formation and dry weight falling in plants. Selenium application in non-saline conditions also could not result to the considerable benefits in sunflower plants.