Chitosan-fulvic acid nanoparticles enhance drought tolerance in maize via antioxidant defense and transcriptional reprogramming.

Nanoparticles are promising alternatives to synthetic fertilizers in the context of climate change and sustainable agriculture. Maize plants were grown under gradient concentrations (50 μM, 100 μM, 200 μM, 500 μM, and 1 mM) of chitosan (Ch), fulvic acid (FA) or chitosan-fulvic acid nanoparticles (Ch-FANPs). Based on the overall phenotypic assessment, 100 μM was selected for downstream experiments. Maize plants grown under this optimized concentration were thereafter subjected to drought stress by water withholding for 14 days. Compared to the individual performances, the combined treatment of Ch-FANPs supported the best plant growth over chitosan, fulvic acid, or sole watered plants and alleviated the adverse effects of drought by enhancing root and shoot growth, and biomass by an average 20%. In addition, Ch-FANPs-treated plants exhibited a significant reduction in hydrogen peroxide (HO) content (10%), with a concomitant increase in ascorbate peroxidase (APX) activity (>100%) while showing a reduced lipid peroxidation level observed by the decrease in malondialdehyde (MDA) content (100%) and low electrolyte leakage level. Furthermore, chlorophyll content increased significantly (>100%) in maize plants treated with Ch-FANPs compared to Ch or FA and control in response to drought. The expression of drought-induced transcription factors, ZmDREB1A, ZmbZIP1, and ZmNAC28, and the ABA-dependent ZmCIPK3 was upregulated by Ch-FANPs. Owing to the above, Ch-FANPs are proposed as a growth-promoting agent and elicitor of drought tolerance in maize via activation of antioxidant machinery and transcriptional reprogramming of drought-related genes.