Abstract
Polymeric nanoparticles have emerged as promising nanocarriers for plant growth regulators (PGRs) in agriculture, enhancing plant growth and boosting fruit and cereal yields. Among these, lignin nanoparticles (LNPs) stand out due to their biodegradability and low production cost. However, few studies have evaluated the biological effects of LNPs encapsulating PGRs - particularly their dose-dependent impacts across the entire plant life cycle. Therefore, our study aims to evaluate the efficiency of lignin nanoparticles (LNPs) encapsulating indole-3-acetic acid (IAA) compared with free application of the hormone. We employed a multidisciplinary approach to comprehensively assess the impacts of different LNPs-IAA concentrations. Germination tests and morphometric analyses were conducted, along with anatomical analyses of seeds, seedlings, and vegetative organs using light microscopy. Confocal microscopy analyses to examine LNP uptake and translocation. Additionally, leaf gas exchange parameters and photosynthetic pigment levels were measured. The lignin nanoparticles were also characterized in terms of length, polydispersity index, zeta potential and encapsulation efficiency. All variables were subjected to normality tests, variance analysis, and post-hoc tests. Structural analysis revealed that LNP application did not alter overall plant anatomy architecture, except for inducing differences in xylem area among vegetative organs. Additionally, LNPs were rapidly absorbed by seeds in less than 5 h and were transported exclusively via the apoplastic pathway. The composition of lignin nanoparticles influenced germination rates and time. Application with lower concentrations showed minimal statistical significance, whereas higher concentrations exhibited phytotoxic effects. Thus, our study highlights the critical importance of optimizing nanocarrier concentrations for plant growth enhancement, demonstrating that lignin nanoparticles (LNPs) represent a promising nanoformulation for bioactive compound encapsulation.