Regulation of APX, SOD, and PAL genes by chitosan under salt stress in rapeseed (Brassica napus L.)

Abstract

Salt stress significantly impairs plant growth and productivity. This study evaluated the effects of foliar-applied chitosan on salt stress mitigation in Brassica napus L. under NaCl treatments (0, 50, 100, 150 mM). Plants were treated with chitosan (0, 5, and 10 mg/L), and their physiological, biochemical, and molecular responses were analyzed. Chitosan at 10 mg/L significantly improved biomass production, root development, and photosynthetic efficiency, increasing total chlorophyll content by up to 35% under severe salinity (150 mM NaCl). It enhanced ion homeostasis by reducing sodium (Na⁺) accumulation (up to 19%) and increasing potassium (K⁺) uptake (up to 27%), mitigating ion toxicity. Chitosan at 10 mg/L also improved membrane stability and osmotic adjustment by elevating phenolics (47%), flavonoids (40%), and anthocyanins (60%), particularly under 100 and 150 mM NaCl. Antioxidant defense mechanisms were strengthened, with 10 mg/L chitosan increasing superoxide dismutase (SOD) activity by 15%, ascorbate peroxidase (APX) by 35%, and catalase (CAT) by 168%, leading to a 30% reduction in hydrogen peroxide (H₂O₂) content, primarily under high salinity (100-150 mM NaCl). Additionally, chitosan upregulated the expression of stress-related genes, including SOD (55%), APX (26%), and phenylalanine ammonia-lyase (PAL) (45%), reinforcing the oxidative defense system. These findings highlight chitosan's role in salt tolerance via ion regulation, osmolyte synthesis, and antioxidant modulation, with 10 mg/L being the most effective concentration. Chitosan represents a promising biostimulant for enhancing crop resilience in saline environments. Future research should optimize formulations for large-scale applications and assess long-term effects on soil and plant health.

Keywords: Antioxidant enzymes; Chitosan; Essential elements; Oxidative damage; Salinity.

Fig. 1

Schematic representation of plant response to salinity and chitosan

Fig. 2

Principal Component Analysis (PCA) illustrating the effects of NaCl and chitosan treatments on Brassica napus L. in relation to photosynthetic traits, primary metabolite concentrations, and activities of PAL, APX, and SOD. It also represents the levels of key nutrients such as Ca, Mg, P, K, N, Fe, Na, and Cl. Additionally, the transcript levels of PAL, APX, and SOD, along with those of anthocyanin, phenolic compounds, flavonoids, and total amino acids, are shown. The p-values for all components are below 0.05 with a significance level of alpha = 0.95

Fig. 3

Negative correlations are shown in red, and positive correlations are shown in blue. The correlation coefficients are correlated with both the circle’s size and color intensity

Fig. 4

Pearson heat map of coefficient of correlation and level of significance over different treatments and levels of chitosan with Ca, Mg, P, K, N, Fe, Na, Cl, amino acids, proteins, carbohydrates, pigments, gene expression level of PAL, APX and SOD, and antioxidant enzymes PAL, APX and SOD activities, anthocyanins, phenolics and flavonoids. It varies by color gradient from dark blue for strong negative correlations-which would be R = -1-to dark red, indicating strong positive correlations at R = 1