Chitosan and its Nanoform Regulates Physiological Processes and Antioxidant Mechanisms to Improve Drought Stress Tolerance of Vicia faba Plant

Purpose: Drought stress is an important challenge to global food security and agricultural output. Dramatic and quick climate change has made the problem worse. It caused unexpected impacts on the growth, development, and yield of different plants. Hence, the ultimate yield does not fulfill the required demand. Understanding the biochemical, ecological, and physiological reactions to these pressures is essential for improved management. Chitosan applications have a wide prospect of addressing abiotic issues. Moreover, chitosan and chitosan nanoparticles have a positive impact on increasing plant tolerance to abiotic stress, like drought stress. The current research investigated the consequences of drought stress on the morpho-physiological and biochemical parameters of Vicia faba plants, a comparison of chitosan and chitosan nanoparticles, and their ameliorating capacity towards drought stress. Methods: A pot experiment was conducted to evaluate the beneficial role of either chitosan (0.5, 1.0, and 2.0 gL^− 1) or chitosan NPs (10, 20, and 30 mgL^− 1) in inducing the Vicia faba tolerance to drought stress (60% water field capacity). Results: Drought stress significantly affected vegetative growth parameters of the shoot system, photosynthetic pigments, and indole acetic acid, accompanied by significant increases in vegetative growth parameters of the root system, some chemical composition of dry leaf tissues (total soluble sugar, soluble protein, proline, phenolic compound, glutathione, α tocopherol), hydrogen peroxide, malonialdehyde, lipoxygenase, and antioxidant enzyme activities (catalase, peroxidase, superoxide dismutase, ascorbate peroxidase, glutathione reductase). All applied treatments. chitosan and chitosan nanoparticles, at all concentrations, improved plant tolerance to drought stress via increasing vegetative growth parameters, photosynthetic pigments, indole acetic acid, total soluble sugar, soluble protein, proline, phenolic compound, glutathione, α tocopherol, and antioxidant enzyme activities, accompanied by decreases in hydrogen peroxide, malondialdehyde, and lipoxygenase enzyme. It is worthy to mention that 20 mgL^− 1 chitosan nanoparticles was the most optimal treatment either under well water conditions (90% water field capacity) or drought stress conditions (60% water field capacity). Moreover, it is obvious from these results that the response of bean plants grown under well watered conditions was more pronounced than that of those plants grown under drought stress conditions to 20 mgL^− 1 chitosan nanoparticles. Conclusions: Hence, it can be concluded that chitosan and chitosan nanoparticles can mitigate the negative impacts of drought stress by improving the photosybthetic pigments, endogenous indole acetic acid, and osmolyte contents, as well as the non-enzymatic and enzymatic antioxidant compounds of the Vicia faba plant.