Chitosan pre- and post-treatment modulates molecular and physiological responses to salinity in Brassica Napus L.

Salt stress affects plant growth and development to a great extent in establishing biochemical imbalances and inducing oxidative damage. The effort was undertaken to assess the relative effectiveness of chitosan pre- and post-treatments in relieving salt stress in Brassica napus L., a moderately salt-sensitive oilseed crop, with respect to the expression patterns of P5CS, PIP, and APX genes along with proline and protein accumulation. One factorial experiment was performed under controlled conditions, where the plants were exposed to varying NaCl concentrations (50, 100, 150, and 200 mM), following either the pre-treatment of chitosan (50 mg/L) or post-treatment of chitosan (50 and 100 mg/L). Gene expression analysis by means of qRT-PCR showed a significant (p < 0.05) upregulation under pre-treatment of P5CS and APX, thereby enhancing osmoprotection and antioxidant defense; however, under post-treatment, the response of P5CS and APX was only moderate. Post-treatment levels of proline and total protein were markedly higher as well. Interestingly, proline content increased by approximately 743% in pre-treated plants at 200 mM of NaCl compared to the control (p < 0.05), indicating enhanced stress tolerance. Besides, the plants subjected to pre-treatment were perfectly grown at 200 mM NaCl whereas those subjected to post-treatment were unable to survive at 150 mM. These findings reveal that the salt tolerance mechanism is better gained by chitosan pre-treatment due to osmotic adjustment enhancement and antioxidative mechanism. This study presents the potential of chitosan to be developed as a strategic biostimulant in promoting crop resistance to saline conditions.