Effect of free and nanoencapsulated nitric oxide donor on the response of tree plants during the hardening off process

Nitric oxide (NO) plays a crucial role as a signaling molecule in several biological processes in plants, participating in the response to different types of environmental stresses. The technique of nanoencapsulation of NO donors appears as a promising approach to expand and enable the exogenous application of NO nitric oxide in environmental restoration programs. Therefore, this study aimed to verify the effect of using a NO donor, in free and encapsulated form, on the hardening off of seedlings of three tree species: Hymenaea courbaril L., Amburana cearensis (Allemão) A.C. Smith, and Hymenaea stigonocarpa Mart. ex Hayne. The seedlings were grown for 3 months under moderate shade and translocated to the hardening off sector, where they remained for 3 months under the treatments: chitosan nanoparticles containing S-nitrosoglutathione (NP-CS-GSNO) at concentrations of 0.025, 0.5, 0.1, and 0.2 mM, free S-nitrosoglutathione, at concentrations of 0.1 and 0.2 mM, or the Control. For H. stigonocarpa, treatments with free or nanoencapsulated GSNO did not differ from each other, differing only from the Control. H. courbaril presented similar behavior in relation to growth variables, however, in the analysis of physiological variables, only the NP-CS-GSNO 0.1 and 0.2 mM treatments differed from the other treatments. A. cearensis maintained similar behavior to H. courbaril, with only a difference in the Control treatment in relation to the other treatments. These results indicate that GSNO presents beneficial physiological effects when made available to native forest species, such as H. stigonocarpa, H. courbaril, and A. cearensis, triggering protective and incremental activities regarding photosynthesis, stomatal conductance, and biomass formation.