Effects of Chitosan and Silica Treatments on Sweet Basil Growth and Oxidative Defense System Under Salinity Stress

Abstract

Global climatic change is a major issue that drastically reduces agricultural productivity. Knowing the increasing prevalence of salty soils worldwide, emphasizing the need for innovative strategies to mitigate salt adverse effects. Prior studies have demonstrated the distinct abilities of chitosan and silica to augment plant tolerance against salt stress. However, little is known about how they work together or the specific mechanisms by which they increase salinity stress tolerance. So, the aim of this investigation was to study how chitosan and silica chitosan with 1.5 and 3 gl-1 and silica (0.25, 0.50 and 1.0 gl-1) either chitosan individually or in combination with silica, affected the performance of sweet basil plant growth and bioactive compounds grown under salt stress. Foliar treatment of chitosan with 1.5 and 3 gl-1 and/or silica (0.25, 0.50 and 1.0 gl-1) significantly improved plant growth (plant height, number of
branches/plant as well as herb fresh and dry weight) comparing to untreated seedlings under salinity stress conditions. This enhancement might have resulted from significant increases in endogenous indole acetic acid (IAA), antioxidant compounds such as phenols, flavonoids and ascorbic acid contents and antioxidant activity (DPPH) in addition to antioxidant enzymes (superoxide dismutase SOD, peroxidase POD, catalase CAT and nitrate reductase NR), and some osmotic compounds (such as total soluble sugars TSS, proline, total soluble protein) compared to untreated control plants. Meanwhile, different treatments reduced significantly oxidative stress markers such as hydrogen peroxide H2O2, superoxide radicals (O-• 2) which caused oxidative damages to cell walls expressed as malonaldehyde MDA. Furthermore, different treatments of chitosan and/or silica increased significantly essential oil
percentages. The GC/MS analysis of the essential oils shows that Eucalyptol was the majors in all cases, while Methyl cinnamate was the second major component. Moreover, the synergistic effectiveness of chitosan and silica in improving salinity tolerance was demonstrated by the enhanced growth parameters and oil percentages that resulted from their combined application.